[cmd/opampsupervisor] Support environment variable expansion in supervisor config

[mrsillydog]

Component(s)

cmd/opampsupervisor

Is your feature request related to a problem? Please describe.

Currently, environment variable expansion is not supported in the supervisor configuration. For example, given the following configuration:

server:
  endpoint: ${OPAMP_SERVER_ENDPOINT}
agent:
  executable: /bin/otelcontribcol

and the following environment variable set:

echo $OPAMP_SERVER_ENDPOINT
ws://localhost/v1/opamp

the final configuration does not expand the referenced environment variable to result in a final configuration of:

server:
  endpoint: ws://localhost/v1/opamp
agent:
  executable: /bin/otelcontribcol

Describe the solution you'd like

I'd like to utilize the go.opentelemetry.io/collector/confmap Resolver along with the go.opentelemetry.io/collector/confmap/provider/envprovider and go.opentelemetry.io/collector/confmap/provider/fileprovider Providers to allow for the expansion of environment variables when the supervisor config is read in from file.

Describe alternatives you've considered

No response

Additional context

I'm happy to implement this enhancement if accepted.

[github-actions]

Pinging code owners:

• cmd/opampsupervisor: @evan-bradley @atoulme @tigrannajaryan

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[VihasMakwana]

Hi!

Just so you know, envprovider will only work if following config is supplied:

server:
  endpoint: ${env:OPAMP_SERVER_ENDPOINT}
agent:
  executable: /bin/otelcontribcol

notice the env prefix.

[mrsillydog]

Hi!

Just so you know, envprovider will only work if following config is supplied:

server:
  endpoint: ${env:OPAMP_SERVER_ENDPOINT}
agent:
  executable: /bin/otelcontribcol

notice the env prefix.

Appreciate the call out! I plan to specify env as the default scheme in the resolver settings, so that specifying the prefix is unnecessary:

resolverSettings := confmap.ResolverSettings{
	URIs: []string{configFile},
	ProviderFactories: []confmap.ProviderFactory{
		fileprovider.NewFactory(),
		envprovider.NewFactory(),
	},
	ConverterFactories: []confmap.ConverterFactory{},
	DefaultScheme:      "env",
}