Variable substitution in image tag

[mb720]

Hi Kurt!

I've created a Scala.js sample application using your plugin: https://gitlab.com/bullbytes/scala-js-example
When running the app using docker-compose up, I'd like to use an environment variable to define which tag of the image to use (latest, staging, or production).
The default tag should be latest.

Thus, I added this to my docker-compose.yml, using Docker's variable substitution with default values:

image: registry.gitlab.com/bullbytes/scala-js-example:${APP_DOCKER_IMAGE_TAG:-latest}

While this works using docker-compose up, I run into an error when executing dockerComposeUp in SBT:

Error parsing reference: "registry.gitlab.com/bullbytes/scala-js-example:${APP_DOCKER_IMAGE_TAG:-latest}" is not a valid repository/tag: invalid reference format

Here's my docker-compose.yml.

Thanks!

P.S.: If you have any feedback for my example app (e.g., my build.sbt), I'd be more than glad to hear it. 😊

[kurtkopchik]

Hi @mb720! Very cool project.

So the way that environment variable substitution works with the sbt-docker-compose plugin is that you need to define the environment values (or a task that calculates the environment variable values) in your build.sbt file. The plug-in then substitutes these values in the compose file before passing it on to docker to process. For reference here is the PR that added this feature.

There is also an example project basic-variable-substitution showing how to use the variable substitution feature.

There are two build.sbt settings that can be used to configure environment values in the docker compose file:
variablesForSubstitution =: // A Map[String,String] of variables to substitute in your docker-compose file. These are substituted substituted by the plugin and not using environment variables.
variablesForSubstitutionTask =: // An sbt task that returns a Map[String,String] of variables to substitute in your docker-compose file. These are substituted by the plugin and not using environment variables.

That being said, looking at your example docker compose file, it looks like Docker introduced a new feature starting in the 2.1 version of the compose file format where you can provide a -default value to the environment variable definition:${VARIABLE:-default}

The current sbt-docker-compose plugin code does not handle this -default value setting at the moment and would have to be updated to support it. For now, you would have to use the standard ${VARIABLE} format and perform any default value logic in your build.sbt. It should be possible to make a code update to the plugin so that it knows how to read the new -default value when it exists and use it if nothing was explicitly provided for substitution. I'll have to look into adding this in the future.

I hope this helps!

[dpfeiffer]

@kurtkopchik Handling of the variable substitution default value is something I am as well looking forward to.

[kurtkopchik]

@dpfeiffer & @mb720 - I made an update to the plugin that allows it to now handle docker-compose environment variables that are defined using the ${VARIABLE:-default} format introduced in version 2.1.

If you do not define the environment variable value in the settings variablesForSubstitution or variablesForSubstitutionTask then the default value will be used.

This change has been published in 1.0.22-SNAPSHOT

resolvers += "Sonatype Snapshots" at "https://oss.sonatype.org/content/repositories/snapshots/"
addSbtPlugin("com.tapad" % "sbt-docker-compose" % "1.0.22-SNAPSHOT")

Let me know if you find any issues with it before I merge it to master. Apologies for the delay.

[dpfeiffer]

@kurtkopchik I will try it today

UDATE: Works fine for me.

[kurtkopchik]

@dpfeiffer - Thank you for verifying! The fix for this issue is now included in an official release:

addSbtPlugin("com.tapad" % "sbt-docker-compose" % "1.0.22")