Agent Skills: Docker Knowledge Patch

Docker Knowledge Patch

Claude Opus 4.6 knows Docker Engine through 24.x and Compose through 2.x. This skill provides features from Buildx 0.31.0 (2026-01-22).

Index

| Topic | Reference | Key features | |---|---|---| | Buildx & Bake | references/buildx-bake.md | Rego source policies, --var flag, semvercmp, env lookup disable |

Quick Reference

Source policy enforcement with Rego (Buildx 0.31.0)

Buildx enforces build policies written in Rego (Open Policy Agent). Policies control what sources/images are allowed during builds.

# Explicit policy file
docker buildx build --policy policy.rego .

# Auto-loads Dockerfile.rego or app.Dockerfile.rego alongside the Dockerfile
docker buildx build -f app.Dockerfile .

# Evaluate and test policies
docker buildx policy eval
docker buildx policy test

In Bake, use the policy key or rely on auto-loading:

# docker-bake.hcl
target "app" {
  dockerfile = "Dockerfile"
  policy     = "policy.rego"
}

Bake --var flag (Buildx 0.31.0)

Set HCL variables directly from the command line instead of using environment variables:

docker buildx bake --var FOO=bar --var VERSION=1.2.3

Bake semvercmp function (Buildx 0.31.0)

Stdlib function for semantic version comparisons in Bake HCL files.

Bake env lookup disable (Buildx 0.31.0)

Option to prevent Bake from reading host environment variables, useful for reproducible builds.

Reference Files

| File | Contents | |---|---| | buildx-bake.md | Rego source policy enforcement (auto-loading, explicit --policy, policy eval/test, Bake policy key), --var flag for HCL variables, semvercmp stdlib function, env lookup disable |