What is the role of dockerignore file

Question

How does this file help?

Answer 1

To understand the role of .dockerignore file, let us take a practical example. You may have noticed that if you put a Dockerfile in your home directory and launch a docker build you will see a message uploading context. Right? This means docker creates a .tar with all the files in your home and in all the subdirectories, and uploads this tar to the docker daemon. If you have some huge files, this may take a long time.

In order to avoid this, you might need to create a specific directory, where you put your Dockerfile, and all what is needed for your build. It becomes necessary to tell docker to ignore some files during the build. Hence, you need to put in the .dockerignore all the files not needed for your build

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.