Computed Truth
Bloated containers slow down CI/CD pipelines and increase cloud storage costs. Switching from standard base images like `node:latest` (1GB+) to `node:alpine` (~50MB) is the single most effective optimization. Layer Caching is powerful, but only if your `COPY` commands are ordered correctly (Dependency > Code).
Docker Image Size Optimizer
Estimate Image Footprint
The Technical Proof
Docker images are constructed using a Union File System. The final size is the sum of all unique layers:
$$ Size_{final} = Size_{base} + \sum Size_{layers} $$
- Base Layer: The OS (e.g., Alpine vs Debian). Cannot be shrunk without changing the tag.
- Multi-stage Builds: Allow you to `COPY --from=builder` only the necessary artifacts (e.g., compiled binary or production `node_modules`), discarding the heavy build environment.
- .dockerignore: Prevents the build context from sending unnecessary files (like `.git` history or local `node_modules`) to the daemon.
Step-by-Step Logic
- Base Selection: Identify the starting cost (Debian-based vs Alpine-based).
- Dependency Calculation:
- Standard: Includes devDependencies + build caches.
- Multi-stage: Includes oNLY production dependencies (typically 40-60% smaller).
- Context Cleaning:
- Standard: `COPY . .` often grabs hidden files.
- .dockerignore: Filters local bloat (typically saves 10-50MB depending on project).
- Layer Stacking: Sum the optimized components.