extends server variables substitutions with mpConfig

[andre-doherty]

Describe the use case that you want to enable:
Server variables substitution takes several sources as listed here : https://openliberty.io/docs/latest/reference/config/server-configuration-overview.html

1. variable default values in the server.xml file
2. environment variables
3. bootstrap.properties
4. Java system properties
5. Variables loaded from files in the ${server.config.dir}/variables directory or other directories as specified by the VARIABLE_SOURCE_DIRS environment variable
6. variable values declared in the server.xml file
7. variables declared on the command line

FMU, most of the sources are static, except for xml ones that are reloaded by the application server.
However those require that the configuration files are added / altered at runtime.

It would be a great improvement to adding a hook and take mpconfig source as an extra server variable sources.

Describe why this is important to you:
This would help to solve some tricky use cases such as loading secrets from a vault, when secret might change during the application lifetime.
Eg : unless i am mistaken, to reload at runtime credentials for a database the current choices are :

• one has to be able to change variables refered in authentication alias,
• make use of the kerberos ticketing systems (which is not always available)
• or more complex, implement a dedicated login module that would talk to the vault.

Offering this possibility would also help solving similar issues with container initialized resources.

André

[andre-doherty]

@gcharters : FYI

[jhanders34]

Server variables are a config source for MP Config values as described here. We can get into some interesting circular logic that would need to be worked out if adding MP config as a config source for server variables.

[Emily-Jiang]

Have you tried the variable replacement provided by MP Config?

[andre-doherty]

hello @Emily-Jiang,

well no, i am a bit confused on how could this mecanism help solving that issue ?
Could you please be more specific ?

André

[Emily-Jiang]

In MP Config, you can add custom dynamic config sources. If you update any properties in the config sources, the values will be looked up in the real time. See here for more info.