4. Podman Container Engine

4. Podman Container Engine#

        flowchart LR
    subgraph Docker
        DC[docker CLI] --> DD[dockerd<br/>daemon]
        DD --> C1[Container]
    end
    subgraph Podman
        PC[podman CLI] --> R[conmon + runc<br/>no daemon]
        R --> C2[Container]
        PC --> Pod[Pod<br/>shared namespace]
        Pod --> C3[Container A]
        Pod --> C4[Container B]
    end
    style DD fill:#f99
    style R fill:#9f9

Podman vs Docker#

Feature

Docker

Podman

Architecture

Client-server (daemon)

Daemonless (fork-exec)

Root required

Yes (default)

No (rootless by default)

Pod support

No (compose only)

Native pods

Systemd integration

Limited

Native (quadlet)

K8s YAML generation

No

podman generate kube

CLI compatibility

—

Drop-in replacement

Compose support

Native

podman-compose / docker-compose

Installation#

# Ubuntu
sudo apt-get install podman

# macOS
brew install podman
podman machine init
podman machine start

# Alias for Docker compatibility
alias docker=podman

Basic Commands (Docker-compatible)#

# Run a container
podman run -d --name web -p 8080:80 nginx:1.25-alpine

# List containers
podman ps -a

# Logs
podman logs -f web

# Exec
podman exec -it web /bin/sh

# Stop and remove
podman stop web && podman rm web

# Build image
podman build -t myapp:1.0 .

# Push to registry
podman push myapp:1.0 docker.io/myuser/myapp:1.0

Rootless Containers#

# Podman runs rootless by default
podman run -d --name web -p 8080:80 nginx:1.25-alpine

# Check user namespace mapping
podman unshare cat /proc/self/uid_map

# Rootless networking uses slirp4netns or pasta
podman run --network pasta -p 8080:80 nginx:1.25-alpine

Pods (K8s-like grouping)#

# Create a pod with shared network namespace
podman pod create --name myapp -p 8080:80 -p 3306:3306

# Add containers to the pod
podman run -d --pod myapp --name web nginx:1.25-alpine
podman run -d --pod myapp --name db \
  -e MYSQL_ROOT_PASSWORD=secret mysql:8.0

# Containers in the same pod share localhost
# web can reach db at localhost:3306

# List pods
podman pod ls

# Stop/remove pod (and all containers)
podman pod stop myapp
podman pod rm myapp

Generate Kubernetes YAML#

# Generate K8s YAML from a running pod
podman generate kube myapp > myapp-k8s.yaml

# Play K8s YAML with podman
podman play kube myapp-k8s.yaml

# Tear down
podman play kube --down myapp-k8s.yaml

Systemd Integration (Quadlet)#

Create a .container file in ~/.config/containers/systemd/ (rootless) or /etc/containers/systemd/ (root):

# ~/.config/containers/systemd/web.container
[Container]
Image=nginx:1.25-alpine
PublishPort=8080:80
Volume=web_data:/usr/share/nginx/html:ro

[Service]
Restart=always

[Install]
WantedBy=default.target

# Reload and start
systemctl --user daemon-reload
systemctl --user start web
systemctl --user enable web
systemctl --user status web

Podman Compose#

# Install podman-compose
pip install podman-compose

# Use existing docker-compose.yml
podman-compose up -d
podman-compose down

# Or use docker-compose with podman socket
systemctl --user start podman.socket
export DOCKER_HOST=unix://$XDG_RUNTIME_DIR/podman/podman.sock
docker-compose up -d

Migration from Docker to Podman#

  1. Install Podman and alias docker=podman

  2. Replace Docker socket: enable podman.socket for tools that need it

  3. Update CI/CD: replace docker commands with podman

  4. Systemd services: convert Docker systemd units to Quadlet files

  5. Compose files: use podman-compose or docker-compose with podman socket

  6. Test rootless: ensure your workloads work without root

# Verify compatibility
podman info
podman system connection list
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