October 30, 2022

#How to emulate the x86_64 architecture for development environments on an Apple M1

First of all, let’s get some terminology out of the way. In the wild, the terms x86, x86_64, x64 and amd64 can be used to refer to the same very common Intel based architecture that we find on most PCs and servers out there. In the same vein, the architecture used on Apple M1 processors may be referred to as ARM, ARM64, ARMv8 64 and aarch64.

The most convenient ways of running foreign developer environments on your M1 is using Docker or Lima, depending on your needs. Both leverage QEMU under the hood to handle the actual CPU emulation and do so with different degrees of performance penalties.


If you’re running Docker Desktop, you already have QEMU set up for you. If you’re using another platform as your Docker provider, simply run:

docker run --privileged --rm tonistiigi/binfmt --install all

For a quick and dirty approach, you can use a disposable container for running your environment. For instance, the following command will spawn a Python x86_64 workspace mounting the current folder as a volume and open a shell for you.

docker run -it --rm --platform="linux/amd64" -v ${PWD}:/app -w /app python:3.10 bash

It’s possible to reuse a container if you really want to, but they’re ephemeral by nature, so don’t grow too attached to them. If you’re going down this route, remove --rm and add the --name flag to the command above to make your life easier later.

You can get to know the architecture options you have available for any container image by running:

# Get data (including supported architectures) about an image stored in a remote registry (e.g. Docker Hub)
docker manifest inspect python:3.10

# Get data on an image locally available on your machine
docker image inspect python:3.10

Pro tip: if you execute docker run without specifying a platform, the created container will use the last image pulled regardless of its architecture. This behavior has been confirmed to work on Docker 20.10. See an example:

docker pull python:3.10 
docker run python:3.10 uname -m
# aarch64

docker pull --platform="linux/amd64" python:3.10
docker run python:3.10 uname -m
# x86_64

If your local software project uses a Dockerfile to manage its image build process, you can add the --platform flag to the FROM clause.

FROM --platform="linux/amd64" python:3.10


For developers that are used to work with Linux, Lima can prove itself a powerful addition to their toolbox. Its main use case is running containerd on MacOS, but it can also act as a Docker Desktop replacement or even do generic Virtual Machine management. We’re going to focus on this last one today.

This approach has a more significant performance impact than Docker, but it can be a good combination of compatibility and ease of use for projects that don’t run well within containers.

Let’s use Ubuntu as our base OS here.

limactl start ubuntu-lts

When prompted, select “Open an editor to review or modify the current configuration”. The architecture being used by our VM is determined by the arch field, so just add x86_64 to it. Also, feel free to modify mounts to fit your needs. You’ll likely add a relevant folder from your host machine there (try not to use your entire home folder for that). And don’t forget to add writable: true to it so the guest machine can make changes to your files. Finally, you might want to change the containerd fields to false as well (since we won’t need it).

To get a better understanding of all the customization available on the file you’ve just edited, read the comments here.

After your VM has started, run:

# Open a shell in your new guest machine
limactl shell ubuntu-lts

# Confirm the architecture being run (you should see "x86_64" as the output)
uname -m

Now, you have a more traditional Linux environment ready with volume mounting and port forwarding out of the box. To check if both are running smoothly, go to a mounted folder and run:

python3 -m http.server 9000

On the browser of your host machine, you should be able to access http://localhost:9000 and see a simple web server displaying your files.

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October 23, 2022

#Create a Docker image from scratch using an OS as base

For the purposes of this example, we’ll be using Raspberry Pi OS 64-bit as the base filesystem for our new Docker image. Since this operating system lacks an official one on Docker Hub, it feels like a good fit. However, the principles described here should work well enough for any OS.

Choose an image to download here and save it locally. With unxz, uncompress the file.

unxz 2022-04-04-raspios-bullseye-arm64-lite.img.xz

Since Raspberry Pi OS is distributed as a disk image and not a partition image, we need to mount it with an offset to avoid getting data from the boot partition. Keep in mind that our goal here is to create a Docker image and, for that, we don’t need boot files.

Find the desired partition offset using fdisk.

fdisk -l 2022-04-04-raspios-bullseye-arm64-lite.img

You’re likely to see an output similar to the following:

Disk 2022-04-04-raspios-bullseye-arm64-lite.img: 1,86 GiB, 2000683008 bytes, 3907584 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x0ee3e8a8

Device                                      Boot  Start     End Sectors  Size Id Type
2022-04-04-raspios-bullseye-arm64-lite.img1        8192  532479  524288  256M  c W95 FAT32 (LBA)
2022-04-04-raspios-bullseye-arm64-lite.img2      532480 3907583 3375104  1,6G 83 Linux

From this, we can see that the block size used is 512 and the start block for the root partition is 532480. Therefore, our offset will be 532480 * 512 = 272629760.

Now, let’s mount the relevant partition, gather its contents as a tar file, generate the image and push it to a registry.

mkdir rootfs

mount -o loop,offset=272629760 2022-04-04-raspios-bullseye-arm64-lite.img rootfs

# Keep in mind that a container image is, under the hood, a tar file of tar files
tar -C rootfs -c . | docker import --platform=linux/arm64 - laury/raspberry-pi-os:bullseye-20220404
docker push laury/raspberry-pi-os:bullseye-20220404

umount rootfs

Note: as the time of writing, the --platform flag is ignored by docker import (tested on version 20.10). So, the host architecture is used to determine the platform supported by the generated image. This bug will be resolved on the 22.06 release (see this PR for more information).

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October 12, 2022

#Troubleshoot CORS related issues on API requests

Cross Origin Resource Sharing (a.k.a. CORS) is a powerful, and yet misunderstood, web standard for protecting web APIs from abuse. If you’re anything like me, however, you had your fair share of wasted work hours trying to deal with it from time to time. The concept seems deceptively simple, but the devil is in the details.

First of all, its important to understand that CORS compliance is an optional standard and is mostly enforced by browsers, like Chrome, Firefox and Safari. Therefore, it’s unlikely that you will face issues with it while working with libraries like Python’s Requests or CLI tools like curl.

However, if you have a frontend application running on your browser with a domain like, let’s say, http://localhost:3000, API calls directed to different domains, like https://laury.dev, will be preceded by a preflight request. This determines if the browser will execute the main request or not.

When having problems with this process, you may see an error similar to this on your Chrome console:

Access to XMLHttpRequest at ‘https://laury.dev from origin ‘http://localhost:3000 has been blocked by CORS policy: No ‘Access-Control-Allow-Origin’ header is present on the requested resource.

To reproduce the problem in a more isolated manner, you can use curl to make a preflight request manually. The important parts here are:

  • the HTTP method has to be OPTIONS
  • three headers must be present: Access-Control-Request-Method, Access-Control-Request-Headers and Origin. Be wary, however, that the domain stated on Origin must mention protocol, FQDN, port (if any is being used), and no trailing slash.

Here’s an example:

curl -IX OPTIONS https://google.com \
    -H "Access-Control-Request-Method: POST" \
    -H "Access-Control-Request-Headers: origin, x-requested-with" \
    -H "Origin: http://mywebsite.com:3000"

For a preflight request to be considered successful, all of the following must be true:

  • the HTTP status on the response is within 200-299
  • the response contains these headers: Access-Control-Allow-Methods, Access-Control-Max-Age and Access-Control-Allow-Origin. One extra catch here is that this last header cannot present the value * when the main request contains authentication information (like cookies). If it does, the preflight will be considered a failure by the browser. In this case, the header has to mention the origin domain explicitly.

Kubernetes users running Ingress Nginx

To manage CORS headers on Ingress Nginx, you may use these annotations on Ingress objects. Even objects that only manage paths inside domains will work with them, so there’s no need to enable CORS on the entire domain if you don’t feel like it.

Further reading

Light overview of preflight requests

Official specification of the Fetch standard for preflight requests

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October 03, 2022

#Use Lima as a Docker Desktop replacement on MacOS

Lima (short for Linux on Mac) is a Virtual Machine management tool for running Linux boxes (think Vagrant, but for development tooling). It focuses on offering a convenient way to run and interact with containerd, but its high customizability allows for a lot more. The examples folder in its repository gives a good idea of what it’s capable.

For running Lima as a Docker Desktop replacement, the official example provided is a great starting point with a few shortcomings:

  • mounting only a temporary folder (/tmp/lima) as writable
  • using sshfs as the mount type (this can cause problems with containers that run chown on startup like Jupyter and Gogs)
  • not including support for building and running multi-arch containers

To circumvent these issues, download this YAML and run:

limactl start docker.yml

If docker login gives you trouble, make sure that ~/.docker/config.json uses osxkeychain as the credsStore. Example:

  "auths": {},
  "credsStore": "osxkeychain"

Further reading

Filesystem mounts available for Lima

VM customization options

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July 03, 2022

#Use iptables to allow only Cloudflare HTTP requests to target your server

If you’re using Cloudflare to protect HTTP endpoints, it might be worth it to block any web traffic that doesn’t come from their servers.

To do that, let’s use iptables. The following commands will do the trick, but take note that these IPs might change in the future.

# Allow IPv4 traffic
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT
iptables -I INPUT -p tcp -m multiport --dports http,https -s -j ACCEPT

# Allow IPv6 traffic
ip6tables -I INPUT -p tcp -m multiport --dports http,https -s 2400:cb00::/32 -j ACCEPT
ip6tables -I INPUT -p tcp -m multiport --dports http,https -s 2606:4700::/32 -j ACCEPT
ip6tables -I INPUT -p tcp -m multiport --dports http,https -s 2803:f800::/32 -j ACCEPT
ip6tables -I INPUT -p tcp -m multiport --dports http,https -s 2405:b500::/32 -j ACCEPT
ip6tables -I INPUT -p tcp -m multiport --dports http,https -s 2405:8100::/32 -j ACCEPT
ip6tables -I INPUT -p tcp -m multiport --dports http,https -s 2a06:98c0::/29 -j ACCEPT
ip6tables -I INPUT -p tcp -m multiport --dports http,https -s 2c0f:f248::/32 -j ACCEPT

Now, block everything else on ports 80 and 443.

iptables -A INPUT -p tcp -m multiport --dports http,https -j DROP
ip6tables -A INPUT -p tcp -m multiport --dports http,https -j DROP

Test your new rules and save your changes to persist them across reboots.

netfilter-persistent save

Further reading

Cloudflare’s IP list

Official Cloudflare recommendations to protect your origin servers

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July 02, 2022

#Basic survival guide and commands for iptables

iptables is a Linux firewall tool that manages packet routing and can block or allow traffic based on rules like a packet’s origin or destination.

Its settings are organized in tables which contain sets of rules, called chains, that will filter data packets.

# Check current configuration
iptables -L -v

# Accept all requests from an IP
iptables -A INPUT -s <ip> -j ACCEPT

# Drop all requests from an IP
iptables -A INPUT -s <ip> -j DROP

# Drop all requests from a range of IPs
iptables -A INPUT -m iprange --src-range <ip_range_start>-<ip_range_end> -j DROP

# Drop all traffic (must be run after acceptance rules)
iptables -A INPUT -j DROP

# Delete all current rules
iptables -F

# Persist changes to disk
# Depending on your setup, you may need to run another command instead
netfilter-persistent save

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June 26, 2022

#Protect public URLs with ModSecurity for Nginx on a Kubernetes cluster

If you’re using Ingress Nginx to manage public endpoints, ModSecurity is already installed, but it’s disabled by default. To enable it, add the following to the ConfigMap ingress-nginx-controller:

allow-snippet-annotations: "true"
enable-modsecurity: "true"
enable-owasp-modsecurity-crs: "true"
modsecurity-snippet: |-
  SecRuleEngine On
  SecRequestBodyAccess On

Customize ModSecurity rules on a per host basis

It’s possible to adjust the ModSecurity configuration for each Ingress object on the cluster using annotations.

  nginx.ingress.kubernetes.io/enable-modsecurity: "true"
  nginx.ingress.kubernetes.io/enable-owasp-core-rules: "false"
  nginx.ingress.kubernetes.io/modsecurity-snippet: |
    SecRuleRemoveById <rule_id>

How to completely customize modsecurity.conf

With the modsecurity-snippet option, its possible to add custom configuration to ModSecurity. However, you can override the modsecurity.conf entirely if you want.

To do so, first copy the file inside the pod.

kubectl -n ingress-nginx cp <ingress-controller-pod-name>:/etc/nginx/modsecurity/modsecurity.conf ./modsecurity.conf

Modify it as required and save the file in a ConfigMap.

kubectl -n ingress-nginx create configmap modsecurityconf --from-file=modsecurity.conf

If, after creating the initial version, you need to change the file again locally, you can update the ConfigMap by doing the following.

kubectl -n ingress-nginx create configmap modsecurityconf \
  --from-file=modsecurity.conf -o yaml \
  --dry-run=client | kubectl apply -f -

To mount the ConfigMap to the controller deployment, create a patch file.

      - name: modsecurityconf
          name: modsecurityconf
      - name: controller
        - name: modsecurityconf
          mountPath: "/etc/nginx/modsecurity/modsecurity.conf"
          subPath: modsecurity.conf
          readOnly: true

And then apply the patch file.

kubectl -n ingress-nginx patch deployment/ingress-nginx-controller --patch-file deployment-patch.yml

Further reading

ConfigMap options for Ingress Nginx

Annotations options for Ingress objects

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June 24, 2022

#Host publicly accessible web URLs from a home server using a remote proxy

Ideally, you would be able to open ports 80 and 443 of your public IP address and update DNS entries with solutions like ddclient or DNS-O-Matic.

However, if your ISP blocks direct traffic to those ports, its possible to use a remote server and SSH tunneling to bypass that limitation. With this setup, you can use Kubernetes ingresses normally. From the ingress’ perspective, http traffic will reach your home server directly. Therefore, tooling like Nginx and Cert Manager will work with no special tweaks.

Any Linux box with a public IP can be your remote proxy, but Oracle Cloud has a generous free tier and can be a good starting option. Just remember that the smallest available machine is probably enough for your needs since it will only forward traffic and not really act on it.

After setting up the remote server with your provider of choice, ensure that it has a SSH server running. We’re going to use it to forward network packets for us.

On your remote instance, edit the /etc/ssh/sshd_config file and add GatewayPorts yes to it. Apply the new configuration with service sshd restart.

If you opted for an Oracle Cloud server, go to the Ingress Rules section of the Virtual Cloud Network panel and open ports 80 and 443. Also, adjust iptables in the instance to allow public traffic to ports 80 and 443.

iptables -I INPUT 6 -m state --state NEW -p tcp --dport 80 -j ACCEPT
iptables -I INPUT 6 -m state --state NEW -p tcp --dport 443 -j ACCEPT
netfilter-persistent save

From your home server, you can run a quick test, as long as you already have a HTTP server running locally. Don’t forget to generate a new SSH key for your local server and authorize it on the remote machine. If everything until now went smoothly, you will be able to access a local web endpoint using the remote server IP as the DNS entry for your domain.

ssh -N -R 80:<local_ip>:80 root@<remote_ip>

If the port forwarding worked, you can create deployment files for it so Kubernetes itself can maintain the connection up and running for you. Customize and apply the following to your local cluster.

apiVersion: v1
kind: Namespace
  name: proxy-router

apiVersion: apps/v1
kind: Deployment
  name: autossh-80
  namespace: proxy-router
    app: autossh-80
  replicas: 1
      maxSurge: 0
      maxUnavailable: 1
    type: RollingUpdate
      app: autossh-80
        app: autossh-80
      - name: autossh-80
        image: jnovack/autossh:2.0.1
          - name: SSH_REMOTE_USER
            value: "root"
          - name: SSH_REMOTE_HOST
            value: "<remote_server_ip>"
          - name: SSH_REMOTE_PORT
            value: "22"
          - name: SSH_TUNNEL_PORT
            value: "80"
          - name: SSH_BIND_IP
            value: ""
          - name: SSH_TARGET_HOST
            value: "<local_server_ip>"
          - name: SSH_TARGET_PORT
            value: "80"
          - name: SSH_MODE
            value: "-R"
          - name: keys
            mountPath: /id_rsa
      nodeName: <node_with_ingress_enabled>
      hostNetwork: true
        - name: keys
            path: <node_path_for_ssh_keys>
            type: File

To redirect port 443 as well, create another deployment using the previous one as a reference.

Any public URLs should, of course, have their DNS entries pointing to the remote server’s IP.

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February 12, 2022

#Manually control a webcam using the command line on Linux

Any webcam compatible with the USB Video Class (UVC) standard should expose an API usable via v4l2-ctl.

Use the following command to check which devices are connected to your computer at the moment.

v4l2-ctl --list-devices

To check the available controllers for your device, run:

v4l2-ctl --list-ctrls-menus

For me, this feature is specially useful for managing focus, brightness and sharpness. The following commands work well with Logitech C922 at least.

# Manual focus
v4l2-ctl -d /dev/video0 --set-ctrl=focus_auto=0  # default=1
v4l2-ctl -d /dev/video0 --set-ctrl=focus_absolute=0

# Manual light exposure controls
v4l2-ctl -d /dev/video0 --set-ctrl=exposure_auto=1  # default=3 (Aperture Priority Mode)
v4l2-ctl -d /dev/video0 --set-ctrl=exposure_absolute=166  # min=12 max=664 default=166

# Brightness and other useful controls
v4l2-ctl -d /dev/video0 --set-ctrl=sharpness=170  # default=128
v4l2-ctl -d /dev/video0 --set-ctrl=brightness=150  # default=128
v4l2-ctl -d /dev/video0 --set-ctrl=backlight_compensation=1  # default=0

Further reading

v4l2-ctl manual

List of compatible USB Video Class (UVC) devices

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November 24, 2021

#Pull and push container images from and to AWS ECR repositories via Docker CLI

To use the regular Docker CLI with Amazon Elastic Container Registry (Amazon ECR), you have to acquire specific login credentials for it first. Assuming you already got basic AWS credentials, run the following to pass those on to Docker. Just note that, below, AWS_ACCOUNT_ID refers to the repository owner, which may not be your own AWS account.

aws ecr get-login-password --region <AWS_REGION> | docker login -u AWS --password-stdin https://<AWS_ACCOUNT_ID>.dkr.ecr.<AWS_REGION>.amazonaws.com

# Example for the official Sagemaker ECR repository
aws ecr get-login-password --region us-east-1 | docker login -u AWS --password-stdin https://683313688378.dkr.ecr.us-east-1.amazonaws.com

Once you’re logged in, list all available container images in a repository with the following:

aws ecr describe-images --region <AWS_REGION> --registry-id <AWS_ACCOUNT_ID> --repository-name <REPOSITORY_NAME>

# Example for the official Sagemaker ECR repository
aws ecr describe-images --region us-east-1 --registry-id 683313688378 --repository-name sagemaker-scikit-learn

Further reading

Prebuilt Amazon SageMaker Docker Images for Scikit-learn and Spark ML

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November 14, 2020

#Get a Docker container's IP from the command line

When dealing with container IPs, it’s important to take note of which network each container is connected to and which network mode it’s using. The default network mode for a Docker installation is bridge, so I’ll assume you’re using it too.

Any container started with docker run will be attached to a default bridge network. To get its IP on that network, run:

docker inspect --format "{{.NetworkSettings.Networks.bridge.IPAddress}}" <container_name>

Note: the --format flag accepts Go’s template syntax. Take a look at some Docker usage examples.

For containers started with docker-compose, a new bridge network is created. Its default name will be <folder_name>_default, so the above command would look like this:

docker inspect --format "{{.NetworkSettings.Networks.<folder_name>_default.IPAddress}}" <container_name>

In both cases, the received IPs are reachable from the host and from other containers in the same bridge.

Further reading

Official docs on Docker bridge networks

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November 13, 2020

#Simple Docker one-liner to run Jupyter Notebook with Python

The following command will start a Jupyter instance mounting the current folder.

docker run --rm -v ${PWD}:/home/jovyan -p 8888:8888 -e JUPYTER_ENABLE_LAB=yes -e CHOWN_HOME=yes jupyter/scipy-notebook:latest

Explanation about the chosen environment variables:

JUPYTER_ENABLE_LAB=yes  # enable the superior "lab" interface
CHOWN_HOME=yes          # ensure the home directory is writable for Jupyter

Further reading

List of all environment variables available using Docker

Official documentation about Jupyter Docker stacks

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November 12, 2020

#Validate a Jenkinsfile without running it

Jenkins servers have a simple validator to check build files for basic errors without running them. Let’s use curl to send a local file named MyJenkinsfile:

curl --user "<username>:<password>" -X POST -F "jenkinsfile=<MyJenkinsfile" https://<jenkins_host_address>/pipeline-model-converter/validate

The response body will contain validation info.

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September 09, 2020

#Install Kubernetes on Raspberry Pi OS

We’re going to use k3s, a lightweight Kubernetes distribution, to get the most of our hardware. This tutorial uses a Raspberry Pi 4 and the latest version of Raspberry Pi OS 32-bit (formerly known as Raspbian). The 64-bit version is pretty much the same for the purposes of this step by step.

Flash the OS image on your SD Card and, if necessary, add Wi-Fi credentials so you can access it.

Enable cgroups support and disable IPv6 by appending the following on /boot/cmdline.txt (remember that /boot refers to the boot partition on your SD Card).

cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory ipv6.disable=1

Personally, I also recommend disabling swap.

dphys-swapfile swapoff && systemctl disable dphys-swapfile.service

If your workloads won’t require GPU, you may want to change the Memory Split to 16 using raspi-config. You’ll have a little extra RAM this way.

You can force the OS to use legacy iptables to ensure compatibility with older Kubernetes versions, but this step is optional.

iptables -F
update-alternatives --set iptables /usr/sbin/iptables-legacy
update-alternatives --set ip6tables /usr/sbin/ip6tables-legacy

Install and test Docker.

curl -fsSL https://get.docker.com | sh -
# Test if everything is running
docker run hello-world
# Optional: allow the "pi" user to run Docker as well
usermod -aG docker Pi

Install and test k3s.

curl -sfL https://get.k3s.io | INSTALL_K3S_EXEC="--disable=traefik --docker" sh -
# After a minute, you should be able to test it
kubectl get nodes

The kubeconfig yaml will be available at /etc/rancher/k3s/k3s.yaml.

If you have worker nodes to add, use the following command to do so. The cluster token can be found at /var/lib/rancher/k3s/server/node-token on the server node.

curl -sfL https://get.k3s.io | K3S_URL=https://<server_ip>:6443 K3S_TOKEN="<cluster_token>" sh -

Further reading

Configuration options for k3s

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September 08, 2020 (updated at: October 09, 2022)

#Use the RGB Cooling HAT, by Yahboom, with Docker on your Raspberry Pi

This tutorial was tested on a Raspberry Pi 4 with RGB Cooling HAT model “YB-EBV02 VER1.1”, by Yahboom, on 32-bit and 64-bit OS.

The hardware creators do provide installation documentation and official code, but putting all parts together can be challenging.

If you’re willing to use Docker and run the 32-bit version of Raspberry Pi OS, you can activate everything with one command (after enabling I2C with raspi-config).

docker run -d --restart unless-stopped --network host --privileged laury/raspberry-pi-rgb-cooling-hat:latest

To run the software on a 64-bit OS, you’ll need to enable Qemu first and then run the container with the --platform flag.

docker run --privileged --rm tonistiigi/binfmt --install all

docker run -d --restart unless-stopped --platform="linux/arm/v7" --network host --privileged laury/raspberry-pi-rgb-cooling-hat:latest

The container image tagged with latest enables the default functionality of the accessory. If you’d like for the RGBs to the turned off, use the v1.1.0-noRGB image tag.

You can also build the Docker image yourself using the following Dockerfile. Just remember to target ARMv7 architecture. The easiest way to achieve that is to build in the Raspberry Pi itself.

FROM python:2.7

RUN apt update &&\
    apt install -y i2c-tools git

RUN pip install Adafruit-GPIO==1.0.3 \
                Adafruit-BBIO==1.2.0 \
                Adafruit-SSD1306==1.6.2 \
                smbus==1.1.post2 \
                image==1.5.32 \
                vcgencmd==0.1.1 \

RUN git clone --depth 1 https://github.com/raspberrypi/firmware.git &&\
    cp -a firmware/hardfp/opt/vc/* /usr

RUN git clone https://github.com/YahboomTechnology/Raspberry-Pi-RGB-Cooling-HAT.git &&\
    unzip Raspberry-Pi-RGB-Cooling-HAT/4.Python\ programming/RGB_Cooling_HAT.zip &&\
    mkdir /app &&\
    cp -a RGB_Cooling_HAT/* /app &&\
    rm -rf /tmp/*

CMD python /app/RGB_Cooling_HAT.py

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August 29, 2020

#Connect to a headless Raspberry Pi through SSH for the first time

This will work for Raspberry Pi OS (formerly known as Raspbian) and no monitor or keyboard are needed.

After flashing the OS, create a wpa_supplicant.conf file on the boot partition of your SD Card (not the boot folder).

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
country=<Insert 2 letter ISO 3166-1 country code here>

 ssid="<Name of your wireless LAN>"
 psk="<Password for your wireless LAN>"

On the same partition, create an empty file called ssh. It will instruct the OS to enable the SSH server. Also, create your SSH user by creating a file named userconf.txt.

touch ssh

echo <user>:`echo '<pass>' | openssl passwd -6 -stdin` > userconf.txt

To find the Raspberry Pi in your local network, you can use nmap. Assuming your local addresses start with 192.168.0, run:

nmap -sn

If your Pi connected correctly, you will see something similar to the following in the output.

Nmap scan report for raspberrypi (<IP>)
Host is up (0.11s latency).
MAC Address: <MAC> (Raspberry Pi Trading)

Further reading

Official docs on remote access and Wi-Fi settings.

Security concerns on default user and password for SSH

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August 26, 2020

#Combine kubectl and JSONPath to read data from a Kubernetes cluster

To customize how data about cluster objects is presented on the terminal, its possible to use JSONPath syntax. Keep in mind that, under the hood, Kubernetes’ API already sends and receives data in JSON format (the YAMLs we’re used to see are an abstraction to ease reading and editing).

Since data hierarchy on the YAML representation may be a bit off, start by getting a pure JSON version of the data you want to filter.

In the following examples, let’s use a specific deployment.

kubectl -n <my_namespace> get deploy/<my_deployment> -o json

Get only the deployment name.

kubectl -n <my_namespace> get deploy/<my_deployment> -o jsonpath='{.metadata.name}'

range is one of the improvements to JSONPath available here. It iterates over JSON lists and can be paired with @ to make references to each item.

Using both, you can, for instance, print image names for all containers created by a deployment (with line breaks).

kubectl -n <my_namespace> get deploy/<my_deployment> -o jsonpath='{range .spec.template.spec.containers[*]}{@.image}{"\n"}{end}'

A good use case for JSONPath is to list annotations for every deployment in a cluster. Tools like Velero depend on the proper configuration of annotations to do volume backups, so it’s convenient to have a consolidated output.

The following command prints namespace, name and template annotations for every deployment. Additionally, it pipes the list to grep so we can have color highlights.

kubectl get -A deployments -o jsonpath='{range .items[*]}{@.metadata.namespace}{" / "}{@.metadata.name}{"\n"}{@.spec.template.metadata.annotations}{"\n"}{"\n"}{end}' | grep --color "backup.velero.io/backup-volumes\|$"

Note: grep is also matching line endings to ensure all lines are printed.

Further reading

Kubernetes docs on JSONPath

JSONPath evaluator

JSONPath syntax details

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August 23, 2020

#Create, test and run a Java project with Gradle using Docker and no IDE

In order to create and manage Java projects, its common to employ the help of an IDE like IntelliJ IDEA or Eclipse.

However, if you would rather use only the command line, Docker can be a great help.

For convenience and reproducibility, create a Dockerfile in your local filesystem with the following contents.

FROM openjdk:14

ENV GRADLE_HOME=/opt/gradle/gradle-6.4.1

RUN yum install -y wget unzip

RUN wget https://services.gradle.org/distributions/gradle-6.4.1-bin.zip -P /tmp &&\
    unzip -d /opt/gradle /tmp/gradle-*.zip &&\
    rm -rf /tmp/*

Build the Docker image and run a container (takes a while). Again, for convenience, -v and -w are used so that file creations and modifications made inside the container are reflected outside.

docker run --rm -it -v ${PWD}:/app -w /app $(docker build -q .) bash

Now, we can use gradle to create and manage a project from the command line.

# Create a new project
# The "application" template most likely will suit your needs
gradle init

# Run unit tests (if you enabled JUnit during project creation)
gradle test

# Run your code
gradle run

Write source code in src/main/java/<your_package> and test code in src/test/java/<your_package>.

Further reading

Official Gradle guide for Java applications

Docker command line

Gradle command line

List of JUnit Assertions

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August 20, 2020

#Issue Let's Encrypt certificates for domains in a Kubernetes cluster

We will use cert-manager to issue HTTPS certificates for domains served publicly by a Kubernetes cluster.

The application can be installed via Helm, but it’s recommended to install CRDs (Custom Resource Definitions) separately. That may come in handy if you need to delete cert-manager without losing already issued certificates. Don’t forget to change the “version” accordingly on all commands.

kubectl apply --validate=false -f https://github.com/jetstack/cert-manager/releases/download/v0.16.1/cert-manager.crds.yaml

Add JetStack charts to your Helm client.

helm repo add jetstack https://charts.jetstack.io
helm repo update

Install the application.

helm install \
  cert-manager jetstack/cert-manager \
  --namespace cert-manager \
  --version v0.16.1

To issue actual certificates, you will need a production Issuer or ClusterIssuer. The following yaml defines a ClusterIssuer and assumes that you have a nginx ingress controller. If it suit your needs, apply it to your cluster.

apiVersion: cert-manager.io/v1alpha2
kind: ClusterIssuer
  name: letsencrypt-prod
    # The ACME server URL
    server: https://acme-v02.api.letsencrypt.org/directory
    # Email address used for ACME registration
    email: <your_email>
    # Name of a secret used to store the ACME account private key
      name: letsencrypt-prod
    # Enable the HTTP-01 challenge provider
    - http01:
          class: nginx

Verify if your set up is working.

$ kubectl get clusterissuers -A
NAME               READY   AGE
letsencrypt-prod   True    30m

The cert-manager stack will act upon ingresses that comply with a couple of conditions to generate HTTPS certificates. The following example illustrates that. Take special note of the annotations and the “secretName” property under “tls”.

apiVersion: extensions/v1beta1
kind: Ingress
    cert-manager.io/cluster-issuer: letsencrypt-prod
    kubernetes.io/tls-acme: "true"
  name: nginx-ingress
  namespace: ingress-testing
  - host: <public_URL>
      - backend:
          serviceName: <service_name>
          servicePort: 80
  - hosts:
    - <public_URL>
    secretName: <secret_name_of_your_choosing>

Rancher users

If you’re installing the Helm Chart via Rancher, you may see the error release cert-manager failed: resource's namespace kube-system doesn't match the current namespace cert-manager. This happens because cert-manager tries to make changes to more than one namespace and Rancher doesn’t support that. There is an issue discussing this.

Thankfully, cert-manager offers an option to only operate in one namespace. Set “global.leaderElection.namespace” to “cert-manager” to achieve this.

helm install \
  cert-manager jetstack/cert-manager \
  --namespace cert-manager \
  --version v0.16.1 \
  --set global.leaderElection.namespace=cert-manager

k3s users

In k3s, at least up to version 1.18.x, cert-manager has problems running its webhook. At this time, to deal with this, we have to use an older version of cert-manager that can run without it. Set “webhook.enabled” to “false” and use v0.13.1.

helm install \
  cert-manager jetstack/cert-manager \
  --namespace cert-manager \
  --version v0.13.1 \
  --set webhook.enabled=false

Further reading

Official documentation on the installation process

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August 11, 2020

#Pretty-print JSON files using the command line

If you have either Python 2 or 3 installed, use the “json.tool” module to pretty-print.

python -m json.tool <json_file> | less

You can also stream input to Python instead of passing a file directly.

cat <json_file> | python -m json.tool | less

This may be useful for viewing large minified JSON files that could slow down GUI applications.

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August 03, 2020

#Quick usage examples of "find" on the command line

Search recursively for file names using a regex pattern. Use -name for a case sensitive search.

find . -iname '*<partial_name>*'

Execute a command with every result found.

find . -iname '*.md' -type f -exec ls -lh {} \;

List all files in the current folder (recursively) that contain every string mentioned in the search parameters. You can chain as many search terms as you want. Just remember that the last grep needs to have -l as a parameter instead of -q.

find . -type f -exec grep -q '<string1>' {} \; -exec grep -q '<string2>' {} \; -exec grep -l '<string3>' {} \;

Note: every command needs to be terminated by ; or +. But these signs may need to be escaped as in ; or \;. Outputs given by find will be placed on {}. Multiple uses of -exec are allowed.

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August 02, 2020

#Read Kubernetes API data using Golang

Get the API client.

import (
  metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"

// use the current context in kubeconfig
config, err := clientcmd.BuildConfigFromFlags("", "<path_to_KUBECONFIG>")
if err != nil {

// create the clientset
clientset, err := kubernetes.NewForConfig(config)
if err != nil {

Usage examples:

  • read data about servers
nodeList, err := clientset.CoreV1().Nodes().List(context.TODO(), metav1.ListOptions{})
if err != nil {
  • read data about pods
namespace := "example"  // leave empty to get data from all namespaces
podList, err := clientset.CoreV1().Pods(namespace).List(context.TODO(), metav1.ListOptions{})
if err != nil {

In the above examples, ListOptions can take two important strings, field selectors and label selectors. This can be used for filtering results.

  LabelSelector: "labelName=labelKey",
  FieldSelector: "spec.nodeName=<node_name>",  // Example for filtering by node name

Field selectors and label selectors on this case operate in the same way that the CLI options for kubectl do. So, the same rules apply here.

Further reading

Official docs on Field Selectors and Labels.

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August 02, 2020

#Read Kubernetes metrics-server data using Golang

First, get the metrics API client.

import (
  metricsv "k8s.io/metrics/pkg/client/clientset/versioned"

// Get the config
config, err := clientcmd.BuildConfigFromFlags("", "<path_to_KUBECONFIG>")
if err != nil {

// Get the metrics client
metricsClientset, err := metricsv.NewForConfig(config)
if err != nil {

Get the data and store it in podMetricsList array.

namespace := "example"  // leave empty to get data from all namespaces
podMetricsList, err := metricsClientset.MetricsV1beta1().PodMetricses(namespace).List(context.TODO(), metav1.ListOptions{})
if err != nil {

Iterate over the results found.

for _, v := range podMetricsList.Items {
  fmt.Printf("%s\n", v.GetName())
  fmt.Printf("%s\n", v.GetNamespace())
  fmt.Printf("%vm\n", v.Containers[0].Usage.Cpu().MilliValue())
  fmt.Printf("%vMi\n", v.Containers[0].Usage.Memory().Value()/(1024*1024))

Note: if you’re inspecting pods that may have more than one container, you’ll need to iterate over v.Containers as well.

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August 01, 2020 (updated at: October 03, 2022)

#Receive data from Kubernetes API using curl

Start by running kubectl’s proxy. With its help, we avoid dealing with authentication headers.

kubectl proxy

Test the connection with a basic call.

curl http://localhost:8001/api/

To check the API groups available, access the root.

curl http://localhost:8001/apis/

Based on the group listing, you can infer URLs for resources.

For cluster-scoped resources, use:


And, for namespace-scoped resources:


To get deployment data, for example, the API Group is “apps”, Version is “v1” and Resourcetype is “deployments”. The final request looks like this:

curl http://localhost:8001/apis/apps/v1/deployments

If your Kubernetes cluster has a metrics-server, the following request will get node resource usage data:

curl http://localhost:8001/apis/metrics.k8s.io/v1beta1/nodes

Rancher users

However, if your cluster was created using Rancher, you’ll need “Authorized Cluster Endpoint” enabled, so your requests can reach the API Server directly. Your URL paths will slightly differ from the examples above otherwise.

Using your command line, you’ll also need to select the correct context for kubectl before activating the proxy.

# List available contexts
kubectl config get-contexts

# Select the direct API context
# Its name has the format <cluster_name>-<pilot_name>
kubectl config use-context <direct_context>

Further reading

Overview of the Kubernetes API

More info about API concepts

Accessing the API without kubectl proxy

Full list of Groups, Versions and Resourcetypes

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July 31, 2020

#Activate the replicaset mode in MongoDB

Start the MongoDB daemon with the --replSet flag.

mongod --replSet rs0

After first start, initialize the replica set with the following:

mongo <mongo_host>/<database> --eval "rs.initiate({_id: 'rs0', members: [ { _id: 0, host: '<mongo_host>:27017' } ]})"

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July 23, 2020

#Test networking performance between two Linux machines

Let’s use iperf to measure networking performance. First, set a “server” machine.

iperf -s

From a “client” machine, run the test.

iperf -c <server_ip>

If you are having trouble getting the server’s IP, use ip addr show to find addresses used by the current machine in any connected networks.

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July 23, 2020

#Wipe any filesystem data and partitions from devices on Linux

wipefs should work in most cases to clean filesystems.

# View filesystem data from device
wipefs /dev/<my_device>

# Wipe any filesystem found
wipefs --all /dev/<my_device>

If wipefs can’t detect a filesystem, you can quickly wipe the header data of the device with dd.

dd if=/dev/zero of=/dev/<my_device> bs=1M count=100 oflag=direct,dsync status=progress

You may need to restart your machine to make the filesystem deletion known to the OS, if your device is a “LVM2_member” for instance.

Also, as a last resort, you can completely wipe the device.

dd if=/dev/zero of=/dev/<my_device> bs=1M count=5000000 oflag=direct,dsync status=progress

To delete partitions, sgdisk should work well.

sgdisk --zap-all /dev/<my_device>

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July 16, 2020

#Bootstrap a Go Cobra application with Go Modules

To bootstrap a Go application using Cobra Generator and Go Modules, start by installing the Cobra command line:

# Install Cobra
go get github.com/spf13/cobra/cobra

Initialize your Cobra project, but remember to use your package’s fully qualified name, as in: github.com/laurybueno/kubectl-hoggers. Don’t worry if your package is not publicly available yet. And there is no need to put your source code inside GOPATH anymore (since Go 1.11 at least):

cobra init --pkg-name <fully_qualified_package_name>

Initialize your new module:

go mod init <fully_qualified_package_name>

Get recursively all its dependencies and install it:

go get -d -v ./...
go install -v ./...

Your app’s command line is now ready to be used:


Further reading

Docker and Go: https://www.docker.com/blog/docker-golang/

Go Modules: https://github.com/golang/go/wiki/Modules

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July 16, 2020

#Download files recursively through a FTP connection using wget

Unfortunately, SCP and Rsync aren’t always an option to get our files out of a server. When FTP is all we have, wget can still do a pretty good job and not re-download files you already have, like a primitive Rsync.

wget -nc -nH --cut-dirs=<NUMBER_REMOTE_FOLDERS_TO_CUT_FROM_PATH> --ftp-user='<FTP_USER>' --ftp-password='<FTP_PASSWORD>' -rl 0 -P <LOCAL_PATH> 'ftp://<REMOTE_HOST>/<PATH_TO_FILES>'

Explanation for the used flags:

-nc, --no-clobber                skip downloads that would download to existing files (overwriting them)
-nH, --no-host-directories       don't create host directories
--cut-dirs=NUMBER                ignore NUMBER remote directory components
-r,  --recursive                 specify recursive download
-l,  --level=NUMBER              maximum recursion depth (inf or 0 for infinite)
-P,  --directory-prefix=PREFIX   save files to PREFIX/..

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June 26, 2020

#Check a site's downtime with this bash one-liner

During a site’s downtime, the following line will print the current time and try to access the given URL one time every 2 seconds. Only the received HTTP headers will be shown.

You may find it useful for monitoring downtime while you try to solve a problem.

while true; do date; curl -IX GET '<URL>'; sleep 2; done;

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March 13, 2020

#How to dump and restore MySQL/MariaDB databases

Options for dumping data:

# Directly
mysqldump --databases $MYSQL_DATABASE -u$MYSQL_USER -p$MYSQL_PASSWORD > dump-`date '+%Y_%m_%d__%H_%M_%S'`.sql

# Docker
docker exec -it <container_name> sh -c 'mysqldump --databases $MYSQL_DATABASE -u$MYSQL_USER -p$MYSQL_PASSWORD' > dump-`date '+%Y_%m_%d__%H_%M_%S'`.sql

# Kubernetes (vulnerable to networking failures)
kubectl -n <namespace> exec deploy/<deploy_name> -- bash -c 'mysqldump --databases $MYSQL_DATABASE -u$MYSQL_USER -p$MYSQL_PASSWORD' > dump-`date '+%Y_%m_%d__%H_%M_%S'`.sql

Additionally, if your database operates in a remote server (like Amazon RDS), you may still use a local Docker container for dumping the data.

# Create a local container with the desired version (in this example, MariaDB 10.4 is used)
docker run -it --rm -v ${PWD}:/dump -w /dump mariadb:10.4 bash

# Get the data
mysqldump -h <hostname> --databases <database_name> -u <database_user> --password='<password>' > dump-`date '+%Y_%m_%d__%H_%M_%S'`.sql

For restoring data, you can use:

mysql -u$MYSQL_USER -p$MYSQL_PASSWORD < dump.sql

If you’re using Docker, you can also place dump files on /docker-entrypoint-initdb.d and those will be imported on the first run. Accepted files types are *.sql, *.sql.gz, and *.sh.

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March 11, 2020

#How to publish Ionic apps on the Google Play Store

For this task, we’re going to use Docker to avoid installing the Android SDK on our computer. This is possible thanks to this ionic Docker image.

# Enter in the container command line
docker run -it --rm --net host --privileged -v /dev/bus/usb:/dev/bus/usb -v ~/.gradle:/root/.gradle -v $PWD:/Sources:rw -v /home/<your_user>/.ssh:/root/.ssh hacklab/ionic:android-28 bash

# Install javascript dependencies
npm install

# Execute Ionic build
ionic cordova platform add android
ionic cordova build android --prod --release

# Sign the generated build
jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore ~/.ssh/<your_keystore> platforms/android/app/build/outputs/apk/release/app-release-unsigned.apk myapp
/opt/android-sdk-linux/build-tools/28.0.3/zipalign -v 4 platforms/android/app/build/outputs/apk/release/app-release-unsigned.apk myapp-2.0.0.apk

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March 10, 2020

#How to dump and restore PostgreSQL databases

Options for dumping data:

# Binary mode
pg_dump -Fc -U $POSTGRES_USER $POSTGRES_DB > dump-`date '+%Y_%m_%d__%H_%M_%S'`.psqlc

# SQL mode
pg_dump -U $POSTGRES_USER $POSTGRES_DB > dump-`date '+%Y_%m_%d__%H_%M_%S'`.sql

# Docker and SQL mode
docker exec -it -u postgres <container_name> sh -c 'pg_dump -U $POSTGRES_USER $POSTGRES_DB' > dump-`date '+%Y_%m_%d__%H_%M_%S'`.sql

# Kubernetes and SQL mode (vulnerable to networking failures)
kubectl -n <namespace> exec deploy/postgres -- sh -c 'pg_dump -U $POSTGRES_USER $POSTGRES_DB' > dump-`date '+%Y_%m_%d__%H_%M_%S'`.sql

Options for restoring data:

# Binary mode
pg_restore -O -U $POSTGRES_USER -c -x -n public -d $POSTGRES_DB dump.psqlc

# SQL mode
psql -d $POSTGRES_DB -a -f /backups/dump.sql

If you’re using Docker, you can also place dump files on /docker-entrypoint-initdb.d and those will be imported on the first run. Accepted files types are *.sql, *.sql.gz, and *.sh.

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March 02, 2020

#Format a new SSD/HD drive for usage

# Create the partition
parted --align optimal <raw_device>
mklabel msdos
mkpart primary ext4 0% 100%

# Get the new partition device path

# Make the filesystem
mkfs.ext4 <new_partition_device_path>

# Test the partition
mkdir /tmp/partition-test
mount -t ext4 <new_partition_device_path> /tmp/partition-test

# Get the UUID

# Edit the /etc/fstab to mount partition during boot
UUID=<uuid>     /storage        ext4    defaults,discard        0       2
## OR, if using XFS
UUID=<uuid>     /storage       xfs     defaults        1       2

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July 01, 2019

#Dump and restore data from MongoDB in Docker

# Create the database dump on your server
docker exec <my_mongodb_container> mongodump --archive=/backups/mongodb-`date +%Y%m%d`.gz --gzip --db <database_name>

# Copy it to your local machine, if needed
scp -r <server_user>@<server_ip>:<remote_backup_path> <local_backup_path>

# Restore it directly into a running Docker container
zcat <backup_path> | docker exec -i <my_mongodb_container> mongorestore --archive --drop

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September 01, 2017

#Some useful Vagrant commands

# Bring up the system
vagrant up

# Get into the running virtual machine
vagrant ssh

# Bring the machine down and up again
# (equivalent of running a halt followed by an up)
vagrant reload

# Destroy the current created virtual machines
vagrant destroy