Introduction to Podman

Introduction to Podman

What is Podman?

• Podman is a tool to manage containers (like Docker but without needing a separate server/daemon).
• Containers are lightweight “mini-computers” that package your app and everything it needs to run (code, libraries, etc.).

Why Use Podman?

1. Daemonless: Unlike Docker, Podman doesn’t need a constantly running background service (daemon).
2. Rootless: It lets you run containers as a regular user (not requiring root/admin), making it safer.
3. Docker-compatible: Commands are almost identical to Docker, and it can even use Dockerfiles to build containers.

What is a Daemon?

A daemon is a background program or process that runs continuously in a system, often performing tasks or waiting for requests to handle.

Key Characteristics of a Daemon

1. Background Process: It doesn’t have a graphical interface or terminal window. It works in the background.
2. Starts Automatically: Many daemons start when the system boots (e.g., a web server daemon).
3. Always Running: They keep running and wait for requests (like listening for incoming network connections).

Examples of Daemons

• Handling network requests (e.g., httpd for Apache).
• Scheduling tasks (e.g., cron for automated jobs).
• Managing hardware (e.g., udevd for device management).

Daemon in Containers

• Docker: Docker has a daemon (dockerd) that manages containers. It runs continuously and handles container-related requests like starting/stopping containers, pulling images, etc.
• Podman: Podman is daemonless, meaning it doesn’t have a constantly running process in the background. Instead, each action is executed directly by the command.

Real-Life Analogy

• Daemon = Kitchen: It stays open in the background, ready to prepare meals.
• Requests = Orders: When you place an order, the kitchen (daemon) starts cooking.
• Podman vs Docker:
  • Podman: You cook the meal yourself when needed—no kitchen always running.
  • Docker: The kitchen is always on standby, ready to take orders.

Things You Need to Know to Use Podman

1. Installation

• On Linux: Use your package manager (e.g., sudo apt install podman on Ubuntu).
• On macOS/Windows: Use tools like Homebrew or download from Podman’s website.

2. Podman CLI

• Commands are very similar to Docker (e.g., podman run, podman build).
• Example: Replace docker with podman in most cases.

3. Podman vs Docker

• Podman doesn’t need a daemon.
• It separates user privileges, reducing security risks.

4. Pods

• Podman can run multiple containers together in a Pod (like Kubernetes Pods). They share resources like networking.

Examples

1. Run a Simple Container

podman run --name hello-world-container -d docker.io/library/alpine sleep 1000

Explanation:

• Runs a lightweight Linux (Alpine) container.
• It runs in the background (-d) for 1000 seconds.

2. List All Containers

podman ps

• Shows running containers (use podman ps -a to see all, even stopped ones).

3. Stop and Remove a Container

podman stop hello-world-container
podman rm hello-world-container

4. Build an Image from a Dockerfile

podman build -t my-app .

Explanation:

• Builds a container image called my-app using the Dockerfile in the current directory.

5. Running Multiple Containers in a Pod

podman pod create --name my-pod
podman run --pod my-pod -d nginx
podman run --pod my-pod -d redis

Explanation:

• Creates a pod called my-pod.
• Runs Nginx (a web server) and Redis (a database) in the same pod, sharing the network.

6. Inspect a Container

podman inspect hello-world-container

• Shows detailed information about the container.

7. Export and Import an Image

• Save an image to a file:

  podman save -o my-app.tar my-app

• Load the image back:

  podman load -i my-app.tar