Managing Docker Containers

Container Lifecycle

docker run ──► RUNNING ──► docker stop ──► STOPPED
                │                              │
                │                         docker start
                │                              │
             docker pause                      ▼
                │                           RUNNING
                ▼
             PAUSED

Running Containers

# Run a container (pull image if not local)
docker run nginx

# Run in detached mode (background)
docker run -d nginx

# Run with a name
docker run -d --name my-nginx nginx

# Run and remove container on exit (great for one-off tasks)
docker run --rm alpine echo "hello"

# Run interactively with a shell
docker run -it ubuntu bash

# Map host port 8080 to container port 80
docker run -d -p 8080:80 nginx

# Pass environment variables
docker run -d -e NODE_ENV=production -e PORT=3000 myapp:1.0

# Limit CPU and memory
docker run -d --cpus="0.5" --memory="256m" myapp:1.0

Listing Containers

# List running containers
docker ps

# List all containers (including stopped)
docker ps -a

# Show only container IDs
docker ps -q

# Format output
docker ps --format "table {{.Names}}\t{{.Status}}\t{{.Ports}}"

Inspecting and Logging

# View container logs
docker logs my-nginx

# Follow logs in real time
docker logs -f my-nginx

# Show last 50 lines
docker logs --tail 50 my-nginx

# Show timestamps
docker logs -t my-nginx

# Detailed container metadata (IP, mounts, env vars, etc.)
docker inspect my-nginx

# Extract a specific field with Go template
docker inspect --format '{{.NetworkSettings.IPAddress}}' my-nginx

# Real-time resource usage (CPU, memory, network, disk)
docker stats

# Running processes inside a container
docker top my-nginx

Executing Commands in Running Containers

# Open a shell in a running container
docker exec -it my-nginx bash

# Run a one-off command
docker exec my-nginx nginx -t

# Run as root even if container runs as another user
docker exec -u root -it my-nginx bash

Stopping and Removing

# Graceful stop (SIGTERM, then SIGKILL after 10s)
docker stop my-nginx

# Immediate kill
docker kill my-nginx

# Start a stopped container
docker start my-nginx

# Restart
docker restart my-nginx

# Remove a stopped container
docker rm my-nginx

# Force remove a running container
docker rm -f my-nginx

# Remove all stopped containers
docker container prune

# Stop and remove all containers (careful in production!)
docker stop $(docker ps -q) && docker rm $(docker ps -aq)

Port Mapping

Container ports are private by default. Use -p to expose them:

# -p hostPort:containerPort
docker run -d -p 8080:80 nginx        # http://localhost:8080 → container:80
docker run -d -p 3000:3000 myapp      # same port on both sides
docker run -d -p 127.0.0.1:5432:5432 postgres  # bind to localhost only

# Let Docker assign a random host port
docker run -d -P nginx

# See which ports are mapped
docker port my-nginx

Copying Files

# Copy from container to host
docker cp my-nginx:/etc/nginx/nginx.conf ./nginx.conf

# Copy from host to container
docker cp ./nginx.conf my-nginx:/etc/nginx/nginx.conf

System Cleanup

# Remove everything unused (containers, images, networks, build cache)
docker system prune

# Include unused volumes too
docker system prune --volumes

# Check disk usage
docker system df