PHP Development With Docker: Where Should You Run 'composer install'?

If you're doing local PHP development with Docker, you might be confused as to whether you should be installing Composer dependencies from inside or outside of the container.

Either option will probably work, but it's best to run composer install inside the container rather than outside it, to avoid any issues that may arise from mismatched PHP versions between the container and host, file permissions being different, etc.

That being said, keep in mind that this is only true for local development, when you're mounting your code onto your container. For production your image should be self-contained (i.e. you install your dependencies and copy over your code in the Dockerfile), so you should never find yourself having to mount your app code or dependencies onto the container.