What is Dockerfile.dockerignore and how to use it correctly to exclude unnecessary files?

The dockerignore file plays a critical role when building images, as it determines which files and directories from the project context should not be transferred to the Docker daemon. When you run the build command, the entire current working directory is sent to the Docker server as a context, and without proper filtering, heavy dependency folders, logs, archives, and service files can end up there.

Using this mechanism significantly speeds up the build process by reducing the volume of transmitted data, as well as enhances project security by preventing the accidental leakage of secret keys, environment files with passwords, or git repositories inside the final container.

To configure this, rules are specified in a file named dockerignore, which should be located in the same directory as the main build configuration file. The syntax of this file is largely similar to gitignore syntax, supporting wildcard patterns, comments via the hash symbol, and rule negation using an exclamation mark.

A typical set of exceptions for web applications includes the following elements:

Careful development of the exclusion list ensures that the resulting image turns out as clean, predictable, and secure as possible for further deployment in a production environment.