A set of guidelines for writing and reviewing Dockerfiles and Docker Compose files. Docker packages an application and its dependencies into a container so it can run consistently across environments.

Use it when creating or reviewing container images, Compose setups, build processes, runtime permissions, dependency caching, and image hardening.

It helps reduce image security risks, inefficient builds, oversized runtime images, and unsafe container settings.

docker — Skill by SumonMSelim

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add skills/sumonmselim/agentguard/docker

Any agent

npx skills add SumonMSelim/agentguard --skill docker

Clone the repo

git clone --depth 1 https://github.com/SumonMSelim/agentguard

Made for: Claude Code, Codex.

Per session 38 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 819 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 1 finding. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5	$0.00038	$0.00819
Opus 5	$0.00019	$0.00409
Sonnet 5	$0.00008	$0.00164
Haiku 4.5	$0.00004	$0.00082

Measured 2d ago against content hash 462f04203e97, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

docker scanned grade A with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Asks for rootlowPrivilege escalation

A mod that escalates privileges can change anything on the machine, not only the project.

- Never run as root. Prefer images with built-in non-root user: distroless `nonroot`, `node` user in Node images, `nobody` in Alpine. Otherwise add non-root user and switch: `USER appuser`

Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.

skills/docker/SKILL.md · 59 lines

How it starts

The opening of the file, as written. The whole thing — 59 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Docker

Image security

Never run as root. Prefer images with built-in non-root user: distroless nonroot, node user in Node images, nobody in Alpine. Otherwise add non-root user and switch: USER appuser
Minimal base: distroless, alpine, or official slim variants
Pin by digest or immutable tag. Never FROM node:latest or image: myapp:latest in Compose
Multi-stage builds: build in full image, copy only artifact to minimal runtime image
No build tools in final image
Scan with Trivy or Grype in CI. Fail on critical/high CVEs
Multi-arch: build with --platform linux/amd64,linux/arm64 for cross-platform targets

Dockerfile

One process per container
Enable BuildKit: DOCKER_BUILDKIT=1. Use --mount=type=cache for dependency caches, --mount=type=secret for build-time secrets
COPY specific files. Avoid COPY . . when targeted copy suffices
Layer order: least → most frequently changed. COPY package.json before COPY src/
.dockerignore: exclude .git, node_modules, test files, secrets, .env
Explicit WORKDIR. No implicit root working dir
ENTRYPOINT for executable, CMD for default args
No secrets in ENV, ARG, or RUN — persist in layer history. Use --mount=type=secret
HEALTHCHECK on all long-running services

Runtime

Read-only root filesystem where possible: --read-only
Drop all capabilities, re-add only what's needed: --cap-drop ALL --cap-add NET_BIND_SERVICE
No --privileged in production
Set resource limits: --memory, --cpus
Named volumes for persistent data. No bind mounts in production
No secrets via env vars. Use Docker secrets or mounted secret files
Log rotation: set --log-opt max-size=10m --log-opt max-file=3. Unbounded logs fill disks

Compose

compose.yml for local dev only. Production: Kubernetes, ECS, or equivalent
Explicit dependencies: depends_on + condition: service_healthy
Named volumes for persistent data. Never rely on container filesystem
env_file for local config. Never commit .env with real secrets
restart: unless-stopped for crash-resilient services
Custom networks per service group. Avoid default bridge
profiles: for optional services (e.g. debug tools, mock servers). Keep default startup lean

Read the full file on GitHub · 59 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2d ago First seen · 59 lines · 0 tokens per session scan A 462f04203e97

Subscribe to this mod's changes

docker is a skill published in the GitHub repository SumonMSelim/agentguard (56 stars, last pushed 1mo ago), licensed MIT. It adds 38 tokens to every session and 819 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (asks for root). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

DevOps and cloud Security Writing and docs 公众号

docker

Getting it into your agent

What it costs to keep this loaded

Grade A, and why

Asks for rootlowPrivilege escalation

How it starts

Docker

Image security

Dockerfile

Runtime

Compose

What this file has done since we first saw it

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