.dockerignore

Difficulty: Beginner

Question

What is a .dockerignore file and why is it important for build performance?

Answer

It works exactly like `.gitignore`. It prevents specific files/directories from being sent to the Docker daemon as part of the 'build context'.

**Commonly ignored**: `node_modules`, `.git`, `.env`, and documentation.

Code examples

Typical .dockerignore

# .dockerignore
node_modules
.git
.env
dist
npm-debug.log
Dockerfile
.dockerignore

By ignoring 'node_modules', the 'COPY . .' command won't copy your local, probably OS-specific modules into the Linux-based container.

Key points

• The Dockerfile is usually the first thing listed in the context, but it's often ignored if it doesn't need to be part of the final image.

Concepts covered

Dockerfile, Build Context, Optimization