docker

Skill: docker

Execute, inspect, and manage Docker containers, images, and network components directly via the CLI, adhering to safe operational boundaries.

Core Principles

• Non-Interactive Execution: Never use -it or interactive pseudo-TTY modes when executing container commands autonomously. Always run in detached (-d) or batch execution modes.
• Resource Cleanup: Always use --rm for ephemeral run commands to prevent container accumulation. Clean up unused images regularly using docker system prune, and prune unused volumes with docker volume prune or docker system prune --volumes.
• Absolute Paths for Mounts: When binding volumes via -v, strictly use absolute paths ($PWD or full paths) rather than relative paths.
• JSON Formatting: When querying for container state or image details, prefer structured output (--format '{{json .}}') for robust parsing.

Commands / Usage Patterns

• Run Ephemeral Containers: docker run --rm -v "$PWD":/work -w /work <image> <command>
• Run Detached Services with Port Binding: docker run -d --name <container_name> -p <host_port>:<container_port> <image>
• Execute Commands in Running Container (Non-Interactive): docker exec <container_name> <command> (Avoid -it for automated agent workflows)
• Stream Logs with Timestamps: docker logs --timestamps --tail 50 <container_name>
• Inspect Container Details via JSON: docker inspect --format='{{json .State.Health}}' <container_name>
• List Running Containers (Structured Output): docker ps --format '{"ID":"{{.ID}}", "Image": "{{.Image}}", "Names":"{{.Names}}", "Status":"{{.Status}}"}'
• Build Image with Tags: docker build -t <image_name>:<tag> -f <Dockerfile_path> .

Diagnostics and Troubleshooting

• Debugging Failed Starts: If a container exits immediately, run docker logs <container_name> to trace startup errors.
• Inspecting Mount Permissions: For permission denied errors inside the container, verify host directory permissions or apply SELinux volume labels (:z or :Z).
• Network Resolution Issues: If containers cannot reach each other, verify they share a user-defined network using docker network inspect <network_name>.

What to Avoid

• Do not run interactive sessions (docker run -it or docker exec -it). These will hang automated agents.
• Do not parse tabular docker ps or docker images output using grep or awk when --format json templating is available.
• Do not leak credentials via CLI arguments or environment variables (-e PASSWORD=xyz). Use docker secret (Swarm) or mount credential files securely.

Limitations

• The agent cannot solve authentication steps interactively (e.g., docker login without a password feed).
• Building massive images may exceed time-to-live execution limits; prefer optimized caching.

Related Skills

• shell: You MUST load this skill when handling shell commands with performance monitoring or timeouts.
• dockerfile: You MUST load this skill when writing, reviewing, or optimizing Dockerfiles.