We're developing several Lagom-based Scala micro-services. They are configured using variable replacement in application.conf, eg.
mysql = {
url = "jdbc:mysql://"${?ENV_MYSQL_DATABASE_URL}
During development, we set these variables as Java System Properties via a env.sbt file that calls System.setProperty("ENV_MYSQL_DATABASE_URL", url). This is working fine.
Now I want to deploy this in a container to my local Docker installation. We are using the SbtReactiveAppPlugin to build the Docker image from build.sbt and simply run sbt Docker/publishLocal. This works as expected, a Docker image is created and I can fire it up.
However, passing in environment variables using the standard docker or docker-compose mechanisms does not seem to work. While I can see that the environment variables are set correctly inside the Docker container (verified using env on a bash and also by doing log.debug("ENV_MYSQL_DATABASE_URL via env: " + sys.env("ENV_MYSQL_DATABASE_URL")) inside the service), they are not used by the application.conf and not available in the configuration system. The values are empty/unset (verified through configuration.getString("ENV_MYSQL_DATABASE_URL").toString() and the exceptions thrown by the mysql system and other systems).
The only way I've gotten it to work was by fudging this into the JAVA_OPTS via JAVA_OPTS=-D ENV_MYSQL_DATABASE_URL=..... However, this seems like a hack, and doesn't appear to scale very well with dozens of environment parameters.
Am I missing something, is there a way to easily use the environment variables inside the Lagom application and application.conf?
Thanks!
I've used Lightbend config to configure Lagom services via environment variables in docker containers for many years, so know that it can be done and has been pretty straightforward in my experience.
With that in mind, when you say that they're not used by application.conf, do you mean that they're unset? Note that unless you're passing a very specific option as a Java property, configuration.getString("ENV_MYSQL_DATABASE_URL") will not read from an environment variable, so checking that will not tell you anything about whether mysql.url is affected by the environment variable. configuration.getString("mysql.url") will give you a better idea of what's going on.
I suspect that in fact your Docker image is being built with the dev-mode properties hardcoded in, and since Java system properties take precedence over everything else, they're shadowing the environment variable.
You may find it useful to structure your application.conf along these lines:
mysql_database_url = "..." # Some reasonable default default for dev-mode
mysql_database_url = ${?ENV_MYSQL_DATABASE_URL}
mysql {
url = "jdbc://"${mysql_database_url}
}
In this case, you have a reasonable default for a developer (probably including in the docs some instructions for running MySQL in a way compatible with that configuration). The default can then be overridden via setting a Java property (e.g. JAVA_OPTS=-Dmysql_database_url) or by setting the ENV_MYSQL_DATABASE_URL environment variable.