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Podman

Important

If you already have Docker-Desktop or Docker Engine (Linux) installed and running, skip this step for the demo and go directly to Deploying applications with kubectl

podman is a full replacement of Docker and Docker-For-Desktop. It's the container Swiss-Army knife from RedHat.

What you get with Podman:

  • Multiple image format support, including the OCI and Docker image formats
  • Full management of container lifecycle, Docker CLI replacement
  • Container image management (managing image layers, overlay filesystems, etc)
  • Podman version 3.4+ now support M1 Apple Macs
  • Replaces Docker-for-Desktop and includes a UI
  • no bundled Kubernetes, use kind, minikube, k3s, microk8s...

It can also run and build rootless containers.

Install

OsX Install
brew install podman
Linux Install
# Alpine
sudo apk add podman
Linux Install
# Centos
sudo yum -y install podman
Linux Install
# ubuntu / Debian
apt-get -y install podman

Windows specific

On Windows, each Podman machine is backed by a virtualized Windows System for Linux (WSLv2) distribution. The podman command can be run directly from your Windows PowerShell (or CMD) prompt, where it remotely communicates with the podman service running in the WSL environment.

Please check the docs for specific detailed instructions

Optionally, Download Podman Desktop (UI) from the official website

Setup

By default Podman set up a VM Machine of 1 CPU, 2Gb of memory, 100Gb of disk.

In order to support demo needs create Podman VM with following parameters:

podman machine init \
--cpus=2 \
--memory=4096 \
--disk-size=200 \
--now

# podman machine start # Not required because of --now option

Check Podman is running:

podman info

Make Docker command call Podman, Podman is command-line compatible with Docker:

mv -f /usr/local/bin/docker /usr/local/bin/docker-orig
ln -s /usr/local/bin/podman /usr/local/bin/docker

Point the default Docker socket to the Podman socket. This is needed as some apps use a hardcoded path to Docker:

# This is needed so every app "hardcoded" for Docker will work
export DOCKER_HOST="unix://$HOME/.local/share/containers/podman/machine/podman-machine-default/podman.sock"

Usage

You can use podman to search for well-known images: 

podman search httpd

You can run an image with the same command as with docker:

podman run -d alpine:latest sleep 20

Then, list the running containers multiple times:

podman ps -a
output
CONTAINER ID  IMAGE                             COMMAND     CREATED      STATUS                 PORTS     NAMES
c4b74e45f004  docker.io/library/alpine:latest   sleep 20    2 hours ago  Up 2 hours ago                   loving_wu

You can also use the docker command, as it's executing podman in the background, and podman support all the same arguments:

docker ps -a
output
CONTAINER ID  IMAGE                             COMMAND     CREATED      STATUS                 PORTS     NAMES
c4b74e45f004  docker.io/library/alpine:latest   sleep 20    2 hours ago  Exited (0) 2 hours ago

Tips and Tricks

You can also use Podman to convert a running docker image into a Kubernetes yaml using:

podman generate kube my-running-app -f ~/my-running-app.yaml

You can also convert a yaml file back to bunch of containers run in Podman:

podman play kube /mnt/mysharedfolder/my-running-app.yaml

Warning

Sometimes some pods way complaine with failed to create fsnotify watcher: too many open files.

This is due to the tuning of the machine default values that are too low. Edit the machine:

podman machine ssh
sudo -s

then add those 2 lines in /etc/sysctl.conf:

fs.inotify.max_user_instances = 10240
fs.inotify.max_user_watches = 122880

And execute:

sysctl -w fs.inotify.max_user_instances=10240
sysctl -w fs.inotify.max_user_watches=122880

Next

Podman is a cool alternative to Docker Engine and Docker CLI.

However, Podman does not provide a K8s cluster.

Create a local Kind Kubernetes cluster in next chapter !