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.

Did you set HOSTNAME explicitly as environment variable? "hostname" itself is a program. On which platform do you operate? How looks your application.conf and how do you retrieve the configuration setting? — Schleichardt
– Schleichardt, Commented Sep 12, 2013 at 19:27
Yes, please show us your application.conf and also where you use that in the application as well. — maba
– maba, Commented Sep 12, 2013 at 20:22
Updated question. HOSTNAME is set on the server, nothing special in application.conf besides attempting to set the host.name configuration variable. — tysonjh
– tysonjh, Commented Sep 12, 2013 at 20:45
FWIW I just came across this same annoying discrepancy between the docs and the actual implementation. If I remember correctly this same bug was there a few years back too. Maybe the Typesafe guys has abandoned the Typesafe Config project? — eirirlar
– eirirlar, Commented Nov 19, 2015 at 12:57

tysonjh · Accepted Answer · 2013-09-13 15:05:50Z

8

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.

answered Sep 13, 2013 at 15:05

tysonjh

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1 Comment

Havoc P Over a year ago

What's happening here is that HOSTNAME is a shell variable but not an environment variable. See stackoverflow.com/questions/3341372/… Another way to put it is that HOSTNAME is not "exported" it's just internal to the bash process. In lowlevel terms, when bash forks a child process it doesn't pass unexported variables to the child's environment. The practical implication is that you could solve this by doing export HOSTNAME before you start the JVM.

James Ward · Accepted Answer · 2013-09-12 21:30:29Z

7

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.

answered Sep 12, 2013 at 21:30

James Ward

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2 Comments

tysonjh Over a year ago

If the app is invoked via the shell then this variable should be available

tysonjh Over a year ago

I stand corrected: scala> System.getenv("HOSTNAME") and scala> System.getProperty("HOSTNAME") both return null.

cmbaxter · Accepted Answer · 2013-09-12 21:34:39Z

1

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.

edited Sep 12, 2013 at 21:34

answered Sep 12, 2013 at 21:24

cmbaxter

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1 Comment

tysonjh Over a year ago

You're also correct, the test verified that HOSTNAME appears to be unavailable in the JVM as an environment variable. Thank you

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