Using environment variables to replace variables inside plugin configs does not seem to trigger

[janerjak]

Using environment variables to replace variables inside plugin configs does not seem to trigger

[itzg]

The variable name prefix is important:

https://docker-minecraft-server.readthedocs.io/en/latest/configuration/interpolating/#replacing-variables-inside-configs:~:text=You%20can%20also%20change%20REPLACE_ENV_VARIABLE_PREFIX%2C%20which%20defaults%20to%20%22CFG_%22%2C%20to%20limit%20which%20environment%20variables%20are%20allowed%20to%20be%20used.

By default, for security reasons, it will only access variables that have a name that starts with "CFG_".

[janerjak]

I have to apologize for missing that crucial line in the wiki. That explains my struggles, thanks! Changing REPLACE_ENV_VARIABLE_PREFIX to _ and prefixing every variable worked perfectly. Although curly braces as in ${VAR_NAME} seem to be required as stated in the wiki ($VAR_NAME does not work).

If I understand the good intention behind the required prefix correctly - somebody could push a malicious mod / plugin update that scans for secrets in environment variables and steal them otherwise?

Is that the reason you can not disable this? Setting REPLACE_ENV_VARIABLE_PREFIX to the empty string doesn't seem to work.

[itzg]

I have to apologize for missing that crucial line in the wiki. That explains my struggles, thanks! Changing REPLACE_ENV_VARIABLE_PREFIX to _ and prefixing every variable worked perfectly. Although curly braces as in ${VAR_NAME} seem to be required as stated in the wiki ($VAR_NAME does not work).

If I understand the good intention behind the required prefix correctly - somebody could push a malicious mod / plugin update that scans for secrets in environment variables and steal them otherwise?

Correct.

Is that the reason you can not disable this? Setting REPLACE_ENV_VARIABLE_PREFIX to the empty string doesn't seem to work.

I just tested and setting to empty string disables the prefix as documented:

I created a config/test.cfg file that contained

eula=${EULA}

and used the compose file

services:
  mc:
    image: itzg/minecraft-server
    environment:
      REPLACE_ENV_VARIABLE_PREFIX: ""
      EULA: true
    volumes:
      - ./config:/config
      - ./data:/data

and the file data/config/test.cfg now contains

eula=true

[janerjak]

I have to correct, that works exactly as expected.

Is that the reason you can not disable this? Setting REPLACE_ENV_VARIABLE_PREFIX to the empty string doesn't seem to work.

Before writing this I tested it with my setup multiple times to no avail - but now it works fine.
The only thing I can assume is that there were external factors like Portainer not correctly mapping my stack environment variables. I assume this because the only variables not replaced in my test.cfg are those that have no value. Maybe that was the issue.

Nevertheless, this is resolved for me. I'm still baffled. Sorry for wasting your time.

[janerjak]

Closing this issue. I made some mistake somewhere.

REPLACE_ENV_VARIABLE_PREFIX decides which variables are replaced. The default value is CFG_ meaning only variables like CFG_VAR_1 are replaced. Setting REPLACE_ENV_VARIABLE_PREFIX to the empty string makes docker-minecraft-server replace every variable.