Typesafe Config Environment Variables

Question

Attempting to use ${HOSTNAME} in a config file does not work! According to the documentation, config files should resolve environment variables as mentioned in the docs:

substitutions fall back to environment variables if they don't resolve in the config itself, so ${HOME} would work as you expect. Also, most configs have system properties merged in so you could use ${user.home}.

Is there a way to get hostname into the config file?

Reproduction
Add host.name=${HOSTNAME} to an application.conf file, then try and access it from anywhere. For example try adding

Logger.info(s"Hostname is ${current.configuration.getString("host.name").getOrElse("NOT-FOUND")}")

to the Global.scala.

Environment
This was run on a RHEL6 environment where echo $HOSTNAME produces precise32 so the environment variable exists, this is not the program hostname.

Answer 1

The solution seems to be passing in the hostname via a system property as -Dhost.name=$HOSTNAME or -Dhost.name=$(hostname). I'd imagine in windows it would be something else, but this works for *NIX environments.

Unless anyone can come up with something cleaner this will be the accepted answer.

Answer 2

You should see if calling System.getenv("HOSTNAME") returns a non-null value. If not, then HOSTNAME is not an env variable according to the java runtime which is what is important for mapping that to a config property in typesafe config. I tried this with HOSTNAME and even though I could echo it in bash, it was not available in java as a env substitution. I changed it to USER and everything worked as expected.

Answer 3

This probably isn't working because $HOSTNAME doesn't seem to actually be an environment variable:

jamesw@T430s:~$ echo $HOSTNAME
T430s
jamesw@T430s:~$ export|grep HOSTNAME
jamesw@T430s:~$

So it must be some other special bash thing.