How do I overwrite config settings from an included file - scala

Question

I have defined some akka remote settings in my application.conf:
akka {
actor {
provider = "akka.remote.RemoteActorRefProvider"
warn-about-java-serializer-usage = false
}
remote {
enabled-transports = ["akka.remote.netty.tcp"]
netty.tcp {
hostname = "myhost"
port = 2561
maximum-frame-size = 256000b
}
}
}
But then I have another program that needs to access other configuration settings from my application.conf. But I need to ignore the akka config settings. So I've tried the following for the second program:
include "application"
akka {}
But the akka settings from application.conf are still being applied. I know this because I get a bind exception on the akka port eventhough there should be no remote akka in my second app
What is the best way for me clear/ignore the akka config settings from my application.conf?

Answer 1

Let's say you want to override the akka.remote.netty.tcp.port in your another.conf, you simply
include "application.conf"
akka.remote.netty.tcp.port = 2562
It will override the netty tcp port while leaving the rest unchanged and inherited

Answer 2

After some experimentation, the best bet IMO is to factor out your application.conf so that your common settings are in their own conf files.
So you might put the common settings in a common-settings.conf and then in your Akka application you would have
include "common-settings"
akka {
// Akka settings here
}
And the other modules that need common-settings can just, in their application.conf:
include "common-settings"
This may work better with a multi-module build. If they're the same, e.g., sbt module, then you'll probably replace the canonical application.conf with akka-application.conf and other-application.conf and point your ActorSystem setup code to akka-application.conf instead of application.conf (which probably shouldn't exist in this scenario, as you'd want bare ConfigFactory.load() calls to fail very quickly (the alternative here is to have different programs fighting over who owns application.conf).

Answer 3

The issue you are facing is actually by design. From the HOCON first page documentation:
Duplicate keys are allowed; later values override earlier, except for object-valued keys where the two objects are merged recursively
Therefore, when you add in your second file an akka {} it is just being merged, and not overwritten.
As I can see it, you have 2 options.
Copying the configuration, and override all properties with the one you actually want. That means, that in the second program, you can add:
akka {
actor {
provider = "new value"
warn-about-java-serializer-usage = false
}
remote {
enabled-transports = ["completely new values"]
netty.tcp {
hostname = "etc..."
port = 2561
maximum-frame-size = 256000b
}
}
}
The other option, which I like less, is to overwrite the object called akka. For doing that, you need to assign to it something that is not an object. Otherwise it will just be merged. For instance, if you add the the second program akka=4, so it will completely remove all of the other values. But! In this case, you have your program to deal with those properties to be missing. That means, that somewhere in your code you will have to write something like (don't forget that config throws on missing):
Try(config.getString("akka.actor.provider")).getOrElse(Do something here)
You have to do that because now akka is a string, and you cannot look into that as an object.