Useful Docker Commands and Configurations

This document is a collection of useful commands and configuration snippets for managing Docker and Docker Compose.

Docker Daemon Configuration

You can customize the Docker daemon’s behavior by editing its configuration file, typically located at /etc/docker/daemon.json on Linux.

Example: Set Default IP Address Pools

This helps prevent IP conflicts with other networks in your environment.

1. Create or edit the configuration file:

   sudo mkdir -p /etc/docker
   sudo nano /etc/docker/daemon.json

2. Add the desired configuration. After saving, you must restart the Docker daemon (sudo systemctl restart docker).

   {
     "default-address-pools": [
       {
         "base": "10.10.0.0/16",
         "size": 24
       }
     ]
   }

Container Management

Running Containers with Environment Variables

You can pass environment variables to your container in two main ways:

# Pass variables from a .env file
docker run --rm -it --env-file .env your-image /bin/bash
 
# Pass a single environment variable
docker run --rm -it -e GITHUB_TOKEN=<GITHUB_TOKEN> your-image /bin/bash

Listing Container Ports

Quickly see which ports are mapped for all containers (running and stopped).

docker ps -a --format "table {{.Names}}\t{{.Ports}}"

Keeping a Container Alive for Debugging

If a container’s main process finishes, the container stops. To keep it running for debugging purposes, you can use a command that doesn’t exit.

Add this to your Dockerfile:

# This command will keep the container running indefinitely
ENTRYPOINT ["tail", "-f", "/dev/null"]

Checking Container Logs

Follow the logs of a running container.

docker logs -f <container_name_or_id>

For HTTP scanner, proxy, or API-client testing, see mendhak/http-https-echo. It runs a simple HTTP/HTTPS echo server and prints incoming request details in the container logs.

Stopping All Running Containers

A quick way to stop all active containers.

docker ps -aq | xargs docker stop

Network Management

Creating a Custom Docker Network

Creating custom bridge networks is a best practice for enabling communication between containers while providing better isolation.

sudo docker network create \
  --driver=bridge \
  --subnet=172.28.0.0/24 \
  --ip-range=172.28.0.0/24 \
  --gateway=172.28.0.254 \
  my_custom_network

Docker Compose Snippets

Using an External Network

If you have a pre-existing Docker network, you can connect a Docker Compose service to it.

---
version: "3.8"
services:
  app:
    image: exampleuser/tor-proxy:latest
    container_name: tor-proxy
    restart: unless-stopped
    networks:
      - wan_net
# ...
networks:
  wan_net:
    external:
      name: WAN # This must be the name of an existing Docker network

Managing Volumes in Docker Compose

Docker Compose provides several ways to manage persistent data.

# ...
services:
  my_app:
    image: my_app_image
    volumes:
      # Bind Mount: Maps a host path to a container path
      - ./html:/var/www/html
 
      # Named Volume: Docker manages the volume
      - app_data:/app/data
 
      # Named Volume with NFS driver
      - nfs_share:/mnt/nfs
 
volumes:
  # Basic named volume
  app_data:
 
  # Named volume pointing to a specific location on the host (bind mount)
  test_data:
    driver: local
    driver_opts:
      type: 'none'
      o: 'bind'
      device: '/home/user/managed_network/test'
 
  # Named volume using an NFS share
  # NOTE: The device path is the path on the NFS server itself.
  nfs_share:
    driver: local
    driver_opts:
      type: "nfs"
      o: "addr=10.0.0.20,rw,nolock"
      device: ":/docker_containers/portainer/storage"

To find available NFS shares, you can use showmount:

showmount -e 10.0.0.20

System Maintenance

Prune Unused Resources

Reclaim disk space by removing stopped containers, dangling images, and unused networks and volumes.

docker system prune --all