Podman

Overview

podman is a tool for working with software containers and Kubernetes. It is a popular alternative to Docker.

Installing in macOS

If you previously installed the “Podman Desktop” app, delete it.
If you previously installed podman using Homebrew, enter brew uninstall podman.
Delete any existing podman executables in your PATH by repeatedly entering which podman and deleting the file that finds.
Download the installer for the podman CLI from https://podman.io.
Run that installer.
Enter podman machine init to create a podman machine.
Enter podman machine start to start the podman machine
Enter podman info to verify that the previous commands worked.

I was not able to get the “Podman Desktop” app to work in macOS!

Names

The names of images and containers are composed of three parts and have the syntax {registry}/{repository}:{tag}.

When an image or container is downloaded from the web, the {registry} part indicates the source code registry from which it came.

When an image or container is created locally, the {registry} part cannot be specified and defaults to “localhost”.

The tag part can be used to identify multiple versions of an image or container. When :{tag} is omitted, the tag defaults to “latest”.

Images

To build an image using the Dockerfile file in the current directory, enter the following:

podman build -t {image-name} .

The . at the end indicates that the file Dockerfile can be found in the current directory. This can be replaced by a path to a file that contains instructions for building an image.

To list all the images created on your machine, enter the following:

podman images

To delete an image, enter the following:

podman rmi {name-or-id}

This will fail if the image is being used by an existing container.

If the image was created with a tag, specifying a name to delete must match the pattern {registry}/{repository}:{tag}.

If the image was not created with a tag, specifying a name to delete must match the pattern {registry}/{repository}.

Containers

To create a container using a given image, enter the following:

podman create --name {container-name} {image-name}"

Often the container exposes a given port (container-port) and you want to map that to port on your machine (host-port). This is done by adding the flag -p {host-port}:{container-port} to the previous command. Typically host-port and container-port are the same.

To list all the containers created on your machine, enter one of the following. The -a flag indicates that is should list all containers, not just the ones that are currently running.

podman ps -a
podman container list -a

To start a container in a background process, enter the following:

podman start {name-or-id}

To cause everything the container writes to stdout to also be written to stdout of the current process, add the --attach flag.

To allow the container to read from stdin of the current process, add the --interactive flag.

To view what the container writes to stdout, enter the following:

podman logs {name-or-id}

To stop a running container, enter the following which can take around 10 seconds to complete:

podman stop {name-or-id}

To delete a container, enter the following:

podman rm {name-or-id}

This will fail if the container is currently running.

To create and run a container using a given image in a single command, enter the following:

podman run --name {container-name} {image-name}"

Add the --rm flag to delete the container after it runs.

Add the -d flag to run the container in detached mode which runs it in a background process. When not running in detached mode, the process cannot be stopped by pressing ctrl-c. Instead, open another terminal and stop the container.

Finding Available Containers

podman search docker.io/busybox

Executable Example

Create a new directory and cd into it.
Create the file script.sh containing the following:
```
#!/bin/sh
echo "Hello, World!"
```
Enter chmod a+x script.sh to make it executable.
Enter . ./script.sh to test the script.

Create the file Docker containing the following:

# Use a lightweight base image.
FROM alpine:latest

# Set the working directory in the container
WORKDIR /app

# Copy the local executable (a script here) into the image.
COPY script.sh /app/script.sh

# Give execute permission to the executable.
RUN chmod +x /app/script.sh

# Set the default command to run the executable
CMD ["/app/script.sh"]

Build an image by entering the following:

podman build -t podman-executable-image .

Create a container by entering the following:

podman create --name podman-executable-container podman-executable-image

Start the container by entering the following:
```
podman start podman-executable-container
```
View the output by entering the following:
```
podman logs podman-executable-container
```

Node.js Example

Create a new directory and cd into it.
Enter npm init to create a package.json file.

Add the following scripts in package.json:

"build": "podman build -t podman-node-image .",
"run": "podman run -d -p 3000:3000 --name podman-node-container podman-node-image"

Create the file index.js containing the following:

const http = require('http');
const port = 3000;

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello, Podman!\n');
});

server.listen(port, () => {
  console.log(`Server running on port ${port}`);
});

Create the file Docker containing the following:

# Use an official Node.js runtime as a parent image.
FROM node:latest

# Set the working directory in the container.
WORKDIR /usr/src/app

# Copy package.json and package-lock.json if they exist.
COPY package*.json ./

# Install application dependencies.
RUN npm install

# Copy the rest of the application code.
COPY . .

# Expose the port the app listens on.
EXPOSE 3000

# Define the command to run the app.
CMD [ "node", "index.js" ]

Enter npm run build to build the image.
Enter npm run to run the image in a container.