Overlaying a file in a Docker container allows you to replace a file inside the container with your own custom version. This is useful when you need to customize a file that is used by the container, such as a configuration file.

Using a Bind Mount

To overlay a file in a Docker container, you can use a bind mount option when launching the container. A bind mount allows you to mount a directory or file from the host machine into the container.

Example: Overlaying a File

The following example illustrates how to replace the settings.yml file inside the container with your own customized version:

docker run -d \
  --mount type=bind,source=/path/settings.yml,target=/opt/PasswordPusher/config/settings.yml \
  -p "5100:5100" pglombardo/pwpush:latest

Let’s break down this command:

  • docker run -d: This command runs the Docker container in detached mode.
  • --mount type=bind,source=/path/settings.yml,target=/opt/PasswordPusher/config/settings.yml: This option mounts the settings.yml file from the host machine at /path/settings.yml to the container at /opt/PasswordPusher/config/settings.yml. The type=bind option specifies that this is a bind mount.
  • -p "5100:5100": This option maps port 5100 on the host machine to port 5100 in the container.
  • pglombardo/pwpush:latest: This is the Docker image to use.

How it Works

When you run the container with the --mount option, Docker creates a bind mount that links the settings.yml file on the host machine to the /opt/PasswordPusher/config/settings.yml file in the container. This means that any changes you make to the settings.yml file on the host machine will be reflected in the container, and vice versa.

Best Practices

  • Make sure to specify the correct path to the file you want to overlay on the host machine.
  • Use a consistent naming convention for your files to avoid confusion.
  • Be careful when modifying files in the container, as changes may not be persisted when the container is restarted or deleted.

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