# Podman (OCI Container) Guide

## Quick Start

```bash
# Build
podman build -t argparse-builder .

# Run rootless
podman run -d -p 8080:8080 argparse-builder

# Run with SELinux
podman run -d -p 8080:8080 --security-opt label=type:container_t argparse-builder
```

## Podman vs Docker

| Feature | Podman              | Docker            |
| ------- | ------------------- | ----------------- |
| Daemon  | Daemonless          | Requires daemon   |
| Root    | Rootless by default | Needs root/group  |
| SELinux | Native support      | Additional config |
| Systemd | Native integration  | Third-party       |
| OCI     | Full compliance     | Mostly compliant  |

## Build Commands

### Standard Build

```bash
podman build -t argparse-builder .
```

### Using Containerfile

```bash
podman build -f Containerfile -t argparse-builder .
```

### Multi-architecture

```bash
podman build --platform linux/amd64,linux/arm64 -t argparse-builder --manifest argparse-builder .
```

### Build with cache

```bash
podman build --layers -t argparse-builder .
```

## Rootless Operation

### Setup Rootless Podman

```bash
# Install
sudo dnf install podman

# Configure subuid/subgid (automatic on most systems)
grep $(whoami) /etc/subuid
grep $(whoami) /etc/subgid

# Run rootless
podman run -d -p 8080:8080 argparse-builder

# Verify
podman ps
```

### Port Binding < 1024 (Rootless)

```bash
# Option 1: Use high port and forward
podman run -d -p 8080:8080 argparse-builder
sudo firewall-cmd --add-forward-port=port=80:proto=tcp:toport=8080

# Option 2: Set sysctl
sudo sysctl net.ipv4.ip_unprivileged_port_start=80

# Option 3: Use systemd socket activation
# See systemd section below
```

## SELinux Configuration

### Run with SELinux

```bash
# Default (uses process label)
podman run -d -p 8080:8080 argparse-builder

# Specific label
podman run -d -p 8080:8080 --security-opt label=type:container_t argparse-builder

# Disable SELinux for container (not recommended)
podman run -d -p 8080:8080 --security-opt label=disable argparse-builder
```

### Volume Mounts with SELinux

```bash
# Auto-label volume (recommended)
podman run -d -p 8080:8080 -v ./data:/data:Z argparse-builder

# Shared label (multiple containers)
podman run -d -p 8080:8080 -v ./data:/data:z argparse-builder

# Private label (single container)
podman run -d -p 8080:8080 -v ./data:/data:Z argparse-builder
```

### Check SELinux Context

```bash
# Container process
podman top <container> label

# Volume labels
ls -Z ./data
```

### SELinux Troubleshooting

```bash
# Check denials
sudo ausearch -m avc -ts recent

# Generate policy
sudo ausearch -m avc | audit2allow -M my-argparse
sudo semodule -i my-argparse.pp

# Check booleans
getsebool -a | grep container
```

## Systemd Integration

### Generate Systemd Unit

```bash
# Create container
podman run -d --name argparse-builder -p 8080:8080 argparse-builder

# Generate unit file
podman generate systemd --new --name argparse-builder > ~/.config/systemd/user/argparse-builder.service

# Enable and start
systemctl --user daemon-reload
systemctl --user enable --now argparse-builder
```

### Systemd Unit (Manual)

```ini
# ~/.config/systemd/user/argparse-builder.service
[Unit]
Description=Argparse Builder Container
Wants=network-online.target
After=network-online.target

[Service]
Restart=always
ExecStartPre=/usr/bin/podman pull argparse-builder:latest
ExecStart=/usr/bin/podman run \
    --rm \
    --name argparse-builder \
    -p 8080:8080 \
    --security-opt label=type:container_t \
    argparse-builder:latest
ExecStop=/usr/bin/podman stop -t 10 argparse-builder
ExecStopPost=/usr/bin/podman rm -f argparse-builder

[Install]
WantedBy=default.target
```

### System-wide Service (requires root)

```bash
# Generate for system
sudo podman generate systemd --new --name argparse-builder > /etc/systemd/system/argparse-builder.service

# Enable and start
sudo systemctl daemon-reload
sudo systemctl enable --now argparse-builder
```

## Pod Management

### Create Pod

```bash
# Create pod with port mapping
podman pod create --name argparse-pod -p 8080:8080

# Run container in pod
podman run -d --pod argparse-pod argparse-builder

# List pods
podman pod ps

# Inspect pod
podman pod inspect argparse-pod
```

### Pod with Multiple Containers

```bash
podman pod create --name argparse-stack -p 8080:8080 -p 9090:9090

# Application
podman run -d --pod argparse-stack argparse-builder

# Monitoring (example)
podman run -d --pod argparse-stack prom/prometheus
```

### Pod Systemd Service

```bash
podman generate systemd --new --name argparse-pod > argparse-pod.service
```

## Security Hardening

### Read-only Root

```bash
podman run -d -p 8080:8080 --read-only argparse-builder
```

### No New Privileges

```bash
podman run -d -p 8080:8080 --security-opt=no-new-privileges argparse-builder
```

### Drop Capabilities

```bash
podman run -d -p 8080:8080 --cap-drop=ALL argparse-builder
```

### Resource Limits

```bash
podman run -d -p 8080:8080 \
    --memory=128m \
    --cpus=0.5 \
    --pids-limit=100 \
    argparse-builder
```

### Combined Hardening

```bash
podman run -d -p 8080:8080 \
    --read-only \
    --security-opt=no-new-privileges \
    --cap-drop=ALL \
    --security-opt label=type:container_t \
    --memory=128m \
    --cpus=0.5 \
    argparse-builder
```

## Networking

### Port Mapping

```bash
# Basic
podman run -d -p 8080:8080 argparse-builder

# Different host port
podman run -d -p 3000:8080 argparse-builder

# Specific interface
podman run -d -p 127.0.0.1:8080:8080 argparse-builder
```

### Custom Network

```bash
# Create network
podman network create argparse-net

# Run with network
podman run -d --network argparse-net -p 8080:8080 argparse-builder

# Inspect network
podman network inspect argparse-net
```

### DNS

```bash
# Custom DNS
podman run -d -p 8080:8080 --dns=8.8.8.8 argparse-builder

# Add hosts
podman run -d -p 8080:8080 --add-host=api.local:192.168.1.100 argparse-builder
```

## Storage and Volumes

### Named Volume

```bash
# Create volume
podman volume create argparse-data

# Use volume with SELinux
podman run -d -p 8080:8080 -v argparse-data:/data:Z argparse-builder

# Inspect volume
podman volume inspect argparse-data
```

### Bind Mount

```bash
# Auto-label (Z)
podman run -d -p 8080:8080 -v ./logs:/app/logs:Z argparse-builder

# Shared label (z) - multiple containers
podman run -d -p 8080:8080 -v ./shared:/shared:z argparse-builder
```

### tmpfs Mount

```bash
podman run -d -p 8080:8080 --tmpfs /tmp:rw,size=64m,mode=1777 argparse-builder
```

## Health and Monitoring

### Health Check

```bash
# Check health status
podman healthcheck run argparse-builder

# View logs
podman logs argparse-builder

# Stats
podman stats argparse-builder

# Top processes
podman top argparse-builder
```

### Inspect Container

```bash
# Full inspect
podman inspect argparse-builder

# Specific field
podman inspect --format='{{.State.Health.Status}}' argparse-builder
```

## Registry Operations

### Login

```bash
# Docker Hub
podman login docker.io

# GitHub Container Registry
podman login ghcr.io

# Private registry
podman login registry.example.com
```

### Tag and Push

```bash
# Tag
podman tag argparse-builder ghcr.io/username/argparse-builder:latest

# Push
podman push ghcr.io/username/argparse-builder:latest
```

### Pull

```bash
# Pull image
podman pull ghcr.io/username/argparse-builder:latest

# Pull specific platform
podman pull --platform linux/arm64 ghcr.io/username/argparse-builder:latest
```

## Podman Compose

### Install

```bash
pip3 install podman-compose
```

### podman-compose.yml

```yaml
version: "3"

services:
  argparse-builder:
    build: .
    ports:
      - "8080:8080"
    restart: unless-stopped
    security_opt:
      - label=type:container_t
      - no-new-privileges
    read_only: true
    cap_drop:
      - ALL
    resources:
      limits:
        cpus: "0.5"
        memory: 128M
```

### Usage

```bash
podman-compose up -d
podman-compose logs -f
podman-compose down
```

## Kubernetes with Podman

### Generate K8s YAML

```bash
# From container
podman generate kube argparse-builder > argparse-k8s.yaml

# From pod
podman generate kube argparse-pod > argparse-pod-k8s.yaml
```

### Play Kubernetes YAML

```bash
# Create from YAML
podman play kube argparse-k8s.yaml

# Remove
podman play kube --down argparse-k8s.yaml
```

## Migration from Docker

### Pull Docker Images

```bash
podman pull docker.io/library/nginx
```

### Docker Compatibility

```bash
# Use docker command (alias)
alias docker=podman

# Docker socket emulation
podman system service --time=0 unix:///tmp/podman.sock
export DOCKER_HOST=unix:///tmp/podman.sock
```

### Convert docker-compose

```bash
# Most docker-compose files work with podman-compose
podman-compose -f docker-compose.yml up
```

## Troubleshooting

### Permission Denied (Rootless)

```bash
# Check subuid/subgid
grep $(whoami) /etc/subuid /etc/subgid

# Verify user namespaces
podman unshare cat /proc/self/uid_map

# Reset storage
podman system reset
```

### SELinux Denials

```bash
# Check denials
sudo ausearch -m avc -ts recent | grep podman

# Temporary permissive mode (troubleshooting)
sudo setenforce 0

# Re-enable
sudo setenforce 1
```

### Port Already in Use

```bash
# Find what's using port
ss -tulpn | grep 8080

# Use different port
podman run -d -p 8081:8080 argparse-builder
```

### Storage Issues

```bash
# Check storage
podman system df

# Clean up
podman system prune -a

# Reset storage
podman system reset
```

## Performance Tuning

### Storage Driver

```bash
# Check current driver
podman info --format '{{.Store.GraphDriverName}}'

# Use overlay (default, best performance)
# Already configured in /etc/containers/storage.conf
```

### Network Performance

```bash
# Use host network (best performance, less isolation)
podman run -d --network host argparse-builder
```

### Build Cache

```bash
# Use buildah cache
podman build --layers -t argparse-builder .
```

## CI/CD Integration

### GitLab CI

```yaml
build:
  image: quay.io/podman/stable
  services:
    - podman:dind
  script:
    - podman build -t $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA .
    - podman push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
```

### GitHub Actions

```yaml
- name: Build with Podman
  run: |
    podman build -t argparse-builder .
    podman tag argparse-builder ghcr.io/${{ github.repository }}:latest
    podman push ghcr.io/${{ github.repository }}:latest
```

## Best Practices

1. **Use Rootless** - Run as regular user by default
2. **SELinux** - Keep enabled, use :Z/:z for volumes
3. **Systemd** - Use `podman generate systemd` for services
4. **Security** - Use `--read-only`, `--cap-drop=ALL`, labels
5. **OCI** - Use Containerfile (compatible with Dockerfile)
6. **Pods** - Group related containers in pods
7. **Health Checks** - Include in Containerfile
8. **Resources** - Set limits with `--memory`, `--cpus`

## Quick Reference

```bash
# Build
podman build -t name .

# Run
podman run -d -p 8080:8080 name

# SELinux volume
podman run -v ./data:/data:Z name

# Systemd
podman generate systemd --new name

# Rootless
podman run --userns=keep-id name

# Pod
podman pod create -p 8080:8080
podman run --pod podname name
```