# TIL: Docker Build Cache: The .dockerignore Gotcha
Spent 2 hours debugging why my Docker builds were slow despite using multi-stage builds and proper layer ordering.
The Issue
Every single build was invalidating the cache at the COPY . . step, even when I hadn't changed any code.
The Culprit
My editor was creating .swp files and updating file timestamps. Docker saw these changes and invalidated the cache.
The Fix
Add a proper .dockerignore:
bash
.git
.gitignore
README.md
.env*
node_modules
npm-debug.log
.next
.vscode
*.swp
*.swo
.DS_StoreBuild time went from 5 minutes to 30 seconds.
- *Pro tip:** Treat `.dockerignore` like `.gitignore` - be aggressive about what you exclude!