given

redis {
  host = ${MY_REDIS_HOST}
  port = ${MY_REDIS_PORT}
}

if the following is in the environment:

MY_REDIS_PORT=6378 redis.port=6379

using

data class RedisConfig(host: String, port: Int)

i’ll end up with

RedisConfig("..", 6379)

i was expecting to end up with

RedisConfig("..", 6378)

it's because it's using the env as a property source (for all values)

I guess the preprocessor one should override it

hmm it's tricky to fix

the env var property source like "overlays" on the files

you could disable that

that's applied over the top

you have an env var called 'redis.port' right

which then is the first match when the decoder says "give me a value for redis.port"

The 

EnvironmentVariablesPropertySource

, 

SystemPropertiesPropertySource

 and 

UserSettingsPropertySource

 sources are automatically registered, with precedence in that order

EnvironmentVariablesPropertySource The 

EnvironmentVariablesPropertySource

 reads config from environment variables. It does not map cases so 

HOSTNAME

 does not provide a value for a field with the name 

hostname

. For nested config, use a period to seperate keys, for example 

topic.name

 would override 

name

 located in a 

topic

 parent. Alternatively, in some environments a 

.

 is not supported in ENV names, so you can also use double underscore 

__

. Eg 

topic__name

 would override name in a Topic object. Optionally you can also create a 

EnvironmentVariablesPropertySource

 with 

allowUppercaseNames

 set to 

true

 to allows for uppercase-only names.

what you can do is create your config loader without the default sources, then it won't use that EnvironmentVariablesPropertySource

withDefaultSources(false) on the builder

with the value of

MY_REDIS_HOST

so its another path

now I think about it the EnvironmentVariablesPropertySource might not make a ton of sense

it's just useful if you want to set ENV vars without putting them in files

and you wouldn't need to put it in the hocon at all

which is exactly how you found this to start with