Add a .dockerignore file to the context directory. That will exclude files and directories.

Reference

Benefits

  • Keeps the image size down and free of clutter like docs, the Git repo, cache files, pacakages, and dev files like tests.
  • Improves security - stop local configs with credentials from getting added to the image.
  • Improves build time. Whenever you make a change to a file in the repo recognized by COPY . ., then the entire layer for that has to be rebuilt. So if you have any irrevelant (docs) or frequently changing files (build cache), then ignore those.

Syntax

Add paths .dockerignore in the root of the build context (such as you repo root).

Basics

  • Paths can be mostly like in globs .gitignore.
  • Note that a directory name is sufficient. A trailing slash is useful to indicate a directory but doesn’t changing meaning.
  • You don’t need ** after a directory name.
  • Note that a leading forward slash is implied. i.e. node_modules/ translates to /node_modules.

Advanced

Keep

!temp

Comment

# My comment

If you have abc/node_modules and maybe also your build context is at the root, then you need to add a glob as */node_modules/ to get the rule to work.

You can also add a glob at the end.

*/temp*

And add more levels.

*/*/temp

An optional character with ?.

temp?

Examples

Base

  • .dockerignore 
      .git/

  docs/
  *.md

Packages

For a Python project, ignore your virtual environment:

# ...

venv

For a JS project, ignore the NPM packages. Rather install these from inside the image so the state of the packages outside the image won’t affect it.

# ...

node_modules/

Configs

If you have any secrets:

# ...

.env
app.local.conf

Volume

For a volume of variables files, you might want to prevent the one on the host from added on the host so that there is no confusion. The container will use a volume so that the directory points to the host’s one.

# ...

myapp/var/

Then run:

$ docker run --rm \
  -v "$PWD/myapp/var:/usr/src/app/myapp/var/" \
  my-app