configuration: support environment variables

[muxator]

A common use case when running an application inside Docker is passing configuration parameters via Environment variables.

We could introduce support for reading the values of configuration parameters from environment variables in settings.json, taking inspiration from ElasticSearch's environment variable substitution:

Environment variables referenced with the ${...} notation within the configuration file will be replaced with the value of the environment variable, for instance:

node.name:    ${HOSTNAME}
network.host: ${ES_NETWORK_HOST}

[poVoq]

There are already some unofficial Docker images that support this. Maybe worth a look?

Important would be to be able to set the API key secret via an ENV variable so that on redeployment of the Docker image one doesn't have to manually change all external services to a new random API key. Thanks!

[muxator]

Implemented. The PR is #3572.

Please note that there is going to be a little Etherpad-specific remark, due to being tied to use a JSON file for configuration.
Even when replacing a variable whose value would be a boolean or a number, quotes must be used. Etherpad, then, takes care of converting back the configuration parameter from string to the right type.

The documentation is in https://github.com/ether/etherpad-lite/blob/3b6b12e8482bb641252c2aa8fff225d61cd5225b/settings.json.template.

   "port":   9001,          <-- Literal values. When not using substitution,
   "minify": false              only strings must be quoted: booleans and
   "skin":   "colibris"         numbers must not.

   "port":   ${PORT}        <-- ERROR: this is not valid json
   "minify": ${MINIFY}
   "skin":   ${SKIN_NAME}

   "port":   "${PORT}"      <-- CORRECT: if you want to use a variable
   "minify": "${MINIFY}"        substitution, put quotes around its name,
   "skin":   "${SKIN_NAME}"     even if the required value is a number or a
                                boolean.
                                Etherpad will take care of rewriting it to
                                the proper type if necessary.

[poVoq]

That looks great already.

Any chance to also implement setting the APIKEY.txt (as explained here: https://github.com/ether/etherpad-lite/wiki/HTTP-API ), similar to how this Docker image does it: https://github.com/tvelocity/dockerfiles/tree/master/etherpad-lite ?

Or is there another way (with a volume?) to prevent the API key changing when recreating/updating the docker image?

My use-case: I have Etherpad integrated in Dokuwiki and Nextcloud, and both require setting the API key, and ideally I would not have to change it manually every time the Docker image is updated.

Thanks a lot!

[gobengo]

This is awesome! Thanks for implementing it @muxator

Any possibility of releasing this in a tagged version soon without waiting for other issues slotted for 1.8?

I'd love to be able to use this from an etherpad/etherpad docker image without pinning to the much-looser developer tag.

Thanks again!

[gobengo]

@muxator Here is something I made to run etherpad-lite on kubernetes. https://github.com/gobengo/etherpad-lite

Configuring the database credentials is most appropriate with environment variables (from a k8s secret) in that context, which requires this feature.

But since there isn't a release that has this feature yet, I had to use the 'latest' tag of the docker image.

Just sharing the use case. Thanks again for adding this. Look forward to having it in 1.8