---

paths:

• "**/Dockerfile"
• "**/Dockerfile.*"
• "**/docker-compose*.yml"
• "**/docker-compose*.yaml"
• "**/compose.yml"
• "**/compose.yaml"

---

Docker Cline Rules: Images, Runtime Users and Build Secrets

Conditional Cline rule for Docker. Install it under .clinerules/ only.

Updated for Docker Engine 29, Nov 2026

Do not upgrade dependencies or the framework version unless the task asks.

Keep Engine, BuildKit, and Compose versions as the project already pins them. Engine 29 is the current major to write for when the host is already on it. Do not assume a Compose feature from a newer file works on an older plugin. Read the existing Dockerfile before you add a stage.

Image shape

A multi-stage build compiles in one stage and copies the artifact into a small runtime stage. The runtime stage does not include the compiler, the package manager cache, or the tests. Pin the base image by digest or by a version tag the project already updates on purpose. Do not use latest.

.dockerignore excludes .git, secrets, and local env files. A COPY . . of a context that contains .env bakes the secret into a layer.

Build secrets and runtime

A secret needed at build time uses a BuildKit secret mount. It does not use ARG or ENV for a token, because those stay in history. The final image does not contain the secret file.

The runtime process has a USER that is not root. Files it writes live in a directory that user owns. A healthcheck hits the app's ready endpoint. The process handles SIGTERM so a stop is not a kill ten seconds later.

Compose and privileges

Compose declares the same user, a read-only root filesystem when the app can live with it, and no extra capabilities. Do not mount /var/run/docker.sock into an application container. Do not set privileged: true to fix a permission error. Fix the user or the volume.

Ports bind to the interface the project intends. A database port is not published on the public interface for a local convenience that will be copied to production.

Checks

Build the image and scan the history for ENV secrets and a root user when the user asked you to build. docker history and a config linter are the evidence. Record the command. Do not push the image.

Mistakes to avoid

• latest as a base tag.
• A token in ARG or ENV.
• A root USER in the runtime stage.
• The Docker socket mounted into the app.
• A single-stage image that ships the toolchain.

What changed in this major

Engine 29 is the current major. BuildKit secrets and a non-root USER are the defaults to write.

Deprecated APIs to never generate

Do not write a top-level version: key in a Compose file. Current Compose treats that key as obsolete and ignores it.

Commands

Run docker build only when asked. Do not push.

Example

FROM node:22-bookworm-slim
USER node