Took me hours to realise why docker build ignores my .dockerignore

November 26, 2017

From the official docs of docker for .dockerignore:

Before the docker CLI sends the context to the docker daemon, it looks for a file named .dockerignore in the root directory of the context. If this file exists, the CLI modifies the context to exclude files and directories that match patterns in it. This helps to avoid unnecessarily sending large or sensitive files and directories to the daemon and potentially adding them to images using ADD or COPY.

Docker CLI will only look for .dockerignore file in the root directory of the context, if you have a monorepo of multiple packages, make sure .dockerignore file is on the root directory of your context, it will ignore it if it is somewhere in the subfolder.

About pattern matching of the ignored file, */temp will match a/temp and b/temp but not temp or a/b/temp from the root directory. To match 2 levels deep only, you need to write */*/temp and for arbitrary levels, use ** it will match any number of directory including zero, eg: **/temp matches temp, a/temp and a/b/temp !

Further reading:

To understand more why you should not ignore .dockerignore, read this article. It gives a lot of insight why .dockerignore file is important.