draky-entrypoint addon

Introduction

draky-entrypoint is an addon that can provide your services with a special entrypoint. It doesn't disable the image's existing entrypoint: it runs its custom entrypoint first, and then executes the original entrypoint and the main command.

The following features will work as long as the addon is installed and enabled for the given service.

Run custom initialization scripts

Scripts inside the container's /draky-entrypoint.init.d directory will run each time the container is started.

How to use it? Just add to your service, in this directory, a volume with your scripts.

Example volume:

  volumes:
    - "./init.d:/draky-entrypoint.init.d:cached,ro"

Override any files inside the container

You can override many files inside the container in a bit cleaner way than adding many volumes. To achieve that, you need to mount a single volume /draky-entrypoint.resources inside the container.

  volumes:
    - "./resources:/draky-entrypoint.resources:cached,ro"

Now inside the ./resources directory on the host, create the override directory, and the directory tree inside this override directory will be merged into the container's directory tree each time the container starts!

So if the content of this ./resources/override directory will be:

./resources/override/etc/php/php.ini
./resources/override/etc/nginx/conf.d/mywebsite.conf

These files will be merged into the container's directory tree each time the container starts.

That way you can customize your containers per-project without having to produce new images.

Variables in the overriding files.

The entrypoint provides a way for substituting variables inside the files in the override directory.

It means that when overriding the container's file, you may use a template with variables, e.g.:

; Unix user/group of processes
; Note: The user is mandatory. If the group is not set, the default user's group
;       will be used.
user = ${DRAKY_OVERRIDE_HOST_USERNAME}
group = ${DRAKY_OVERRIDE_HOST_GROUP}

In this case, you also need to pass these variables into the container by declaring them in the service definition:

environment:
  DRAKY_OVERRIDE_HOST_USERNAME: host
  DRAKY_OVERRIDE_HOST_GROUP: host

Note that the variables available in the overriding files are only variables prefixed with the DRAKY_OVERRIDE_ string.

Note also that because you can use variables from your configuration files in the service definitions, you can pass them into the container and use in your files in the override directory. That way you to some degree you can configure files inside your container with your configuration files on the host.

Environmental variables

You can pass some optional environmental variables to the container that is using draky-entrypoint, to alter its behavior.

DRAKY_ENTRYPOINT_DO_CREATE_HOST_USER - if this variable has a value, the draky-entrypoint will create a user with the name host, with the same id as value of this variable. Why would you want to use it? For example: if you want to run something inside the container as a host. That way you will have access to the files created by this process. A common use case would be php-fpm.