Docker Management

Manage Docker containers, images, volumes, networks, and Compose stacks — lifecycle ops, debugging, cleanup, and Dockerfile optimization.

Skill metadata


Source	Optional — install with `hermes skills install official/devops/docker-management`
Path	`optional-skills/devops/docker-management`
Version	`1.0.0`
Author	sprmn24
License	MIT
Platforms	linux, macos, windows
Tags	`docker`, `containers`, `devops`, `infrastructure`, `compose`, `images`, `volumes`, `networks`, `debugging`

Reference: full SKILL.md

:::info The following is the complete skill definition that Hermes loads when this skill is triggered. This is what the agent sees as instructions when the skill is active. :::

Docker Management

Manage Docker containers, images, volumes, networks, and Compose stacks using standard Docker CLI commands. No additional dependencies beyond Docker itself.

When to Use

Run, stop, restart, remove, or inspect containers
Build, pull, push, tag, or clean up Docker images
Work with Docker Compose (multi-service stacks)
Manage volumes or networks
Debug a crashing container or analyze logs
Check Docker disk usage or free up space
Review or optimize a Dockerfile

Prerequisites

Docker Engine installed and running
User added to the docker group (or use sudo)
Docker Compose v2 (included with modern Docker installations)

Quick check:

bash

docker --version && docker compose version

Quick Reference

Task	Command
Run container (background)	`docker run -d --name NAME IMAGE`
Stop + remove	`docker stop NAME && docker rm NAME`
View logs (follow)	`docker logs --tail 50 -f NAME`
Shell into container	`docker exec -it NAME /bin/sh`
List all containers	`docker ps -a`
Build image	`docker build -t TAG .`
Compose up	`docker compose up -d`
Compose down	`docker compose down`
Disk usage	`docker system df`
Cleanup dangling	`docker image prune && docker container prune`

Procedure

1. Identify the domain

Figure out which area the request falls into:

Container lifecycle → run, stop, start, restart, rm, pause/unpause
Container interaction → exec, cp, logs, inspect, stats
Image management → build, pull, push, tag, rmi, save/load
Docker Compose → up, down, ps, logs, exec, build, config
Volumes & networks → create, inspect, rm, prune, connect
Troubleshooting → log analysis, exit codes, resource issues

2. Container operations

Run a new container:

bash

# Detached service with port mapping
docker run -d --name web -p 8080:80 nginx

# With environment variables
docker run -d -e POSTGRES_PASSWORD=secret -e POSTGRES_DB=mydb --name db postgres:16

# With persistent data (named volume)
docker run -d -v pgdata:/var/lib/postgresql/data --name db postgres:16

# For development (bind mount source code)
docker run -d -v $(pwd)/src:/app/src -p 3000:3000 --name dev my-app

# Interactive debugging (auto-remove on exit)
docker run -it --rm ubuntu:22.04 /bin/bash

# With resource limits and restart policy
docker run -d --memory=512m --cpus=1.5 --restart=unless-stopped --name app my-app

Key flags: -d detached, -it interactive+tty, --rm auto-remove, -p port (host:container), -e env var, -v volume, --name name, --restart restart policy.

Manage running containers:

bash

docker ps                        # running containers
docker ps -a                     # all (including stopped)
docker stop NAME                 # graceful stop
docker start NAME                # start stopped container
docker restart NAME              # stop + start
docker rm NAME                   # remove stopped container
docker rm -f NAME                # force remove running container
docker container prune           # remove ALL stopped containers

Interact with containers:

bash

docker exec -it NAME /bin/sh          # shell access (use /bin/bash if available)
docker exec NAME env                   # view environment variables
docker exec -u root NAME apt update    # run as specific user
docker logs --tail 100 -f NAME         # follow last 100 lines
docker logs --since 2h NAME            # logs from last 2 hours
docker cp NAME:/path/file ./local      # copy file from container
docker cp ./file NAME:/path/           # copy file to container
docker inspect NAME                    # full container details (JSON)
docker stats --no-stream               # resource usage snapshot
docker top NAME                        # running processes

3. Image management

bash

# Build
docker build -t my-app:latest .
docker build -t my-app:prod -f Dockerfile.prod .
docker build --no-cache -t my-app .              # clean rebuild
DOCKER_BUILDKIT=1 docker build -t my-app .       # faster with BuildKit

# Pull and push
docker pull node:20-alpine
docker login ghcr.io
docker tag my-app:latest registry/my-app:v1.0
docker push registry/my-app:v1.0

# Inspect
docker images                          # list local images
docker history IMAGE                   # see layers
docker inspect IMAGE                   # full details

# Cleanup
docker image prune                     # remove dangling (untagged) images
docker image prune -a                  # remove ALL unused images (careful!)
docker image prune -a --filter "until=168h"   # unused images older than 7 days

4. Docker Compose

bash

# Start/stop
docker compose up -d                   # start all services detached
docker compose up -d --build           # rebuild images before starting
docker compose down                    # stop and remove containers
docker compose down -v                 # also remove volumes (DESTROYS DATA)

# Monitoring
docker compose ps                      # list services
docker compose logs -f api             # follow logs for specific service
docker compose logs --tail 50          # last 50 lines all services

# Interaction
docker compose exec api /bin/sh        # shell into running service
docker compose run --rm api npm test   # one-off command (new container)
docker compose restart api             # restart specific service

# Validation
docker compose config                  # validate and view resolved config

Minimal compose.yml example:

yaml

services:
  api:
    build: .
    ports:
      - "3000:3000"
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/mydb
    depends_on:
      db:
        condition: service_healthy

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
      POSTGRES_DB: mydb
    volumes:
      - pgdata:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U user"]
      interval: 10s
      timeout: 5s
      retries: 5

volumes:
  pgdata:

5. Volumes and networks

bash

# Volumes
docker volume ls                       # list volumes
docker volume create mydata            # create named volume
docker volume inspect mydata           # details (mount point, etc.)
docker volume rm mydata                # remove (fails if in use)
docker volume prune                    # remove unused volumes

# Networks
docker network ls                      # list networks
docker network create mynet            # create bridge network
docker network inspect mynet           # details (connected containers)
docker network connect mynet NAME      # attach container to network
docker network disconnect mynet NAME   # detach container
docker network rm mynet                # remove network
docker network prune                   # remove unused networks

6. Disk usage and cleanup

Always start with a diagnostic before cleaning:

bash

# Check what's using space
docker system df                       # summary
docker system df -v                    # detailed breakdown

# Targeted cleanup (safe)
docker container prune                 # stopped containers
docker image prune                     # dangling images
docker volume prune                    # unused volumes
docker network prune                   # unused networks

# Aggressive cleanup (confirm with user first!)
docker system prune                    # containers + images + networks
docker system prune -a                 # also unused images
docker system prune -a --volumes       # EVERYTHING — named volumes too

Warning: Never run docker system prune -a --volumes without confirming with the user. This removes named volumes with potentially important data.

Pitfalls

Problem	Cause	Fix
Container exits immediately	Main process finished or crashed	Check `docker logs NAME`, try `docker run -it --entrypoint /bin/sh IMAGE`
"port is already allocated"	Another process using that port	`docker ps` or `lsof -i :PORT` to find it
"no space left on device"	Docker disk full	`docker system df` then targeted prune
Can't connect to container	App binds to 127.0.0.1 inside container	App must bind to `0.0.0.0`, check `-p` mapping
Permission denied on volume	UID/GID mismatch host vs container	Use `--user $(id -u):$(id -g)` or fix permissions
Compose services can't reach each other	Wrong network or service name	Services use service name as hostname, check `docker compose config`
Build cache not working	Layer order wrong in Dockerfile	Put rarely-changing layers first (deps before source code)
Image too large	No multi-stage build, no .dockerignore	Use multi-stage builds, add `.dockerignore`

Verification

After any Docker operation, verify the result:

Container started? → docker ps (check status is "Up")
Logs clean? → docker logs --tail 20 NAME (no errors)
Port accessible? → curl -s http://localhost:PORT or docker port NAME
Image built? → docker images | grep TAG
Compose stack healthy? → docker compose ps (all services "running" or "healthy")
Disk freed? → docker system df (compare before/after)

Dockerfile Optimization Tips

When reviewing or creating a Dockerfile, suggest these improvements:

Multi-stage builds — separate build environment from runtime to reduce final image size
Layer ordering — put dependencies before source code so changes don't invalidate cached layers
Combine RUN commands — fewer layers, smaller image
Use .dockerignore — exclude node_modules, .git, __pycache__, etc.
Pin base image versions — node:20-alpine not node:latest
Run as non-root — add USER instruction for security
Use slim/alpine bases — python:3.12-slim not python:3.12