Add ability to use feature-gates in the operator

[TylerHelmuth]

This PR adds the ability to use feature gates in the operator, but does not add any feature gates specifically. It is based on #1557, but with the most recent featuregate changes. My goal is to add this capability as a standalone PR so it can be used in #1557 and #1555.

Closes #1548

[pavolloffay]

I have the same comments as in the original PR #1557

The package name should probably be changed or include all operator flags. There are as well missing docs.

How do consumers know which feature flags are supported by the operator - take a look at #1557 (comment)

[TylerHelmuth]

@pavolloffay It should be possible to include the list of registered featuregates during startup, I can add that.

Also, how to you feel about the addition of the flag/featuregate package? Should we handle the feature gate flags like we do the rest of the flags in main.go?

[pavolloffay]

We can have a package for it, but the current flags name is too generic and therefore I would expect it handles all operator flags.

[TylerHelmuth]

I have confirmed that the latest featuregate package includes the registered gates as default values:

func main() {
	colfeaturegate.GlobalRegistry().MustRegister("basic", colfeaturegate.StageAlpha)
	colfeaturegate.GlobalRegistry().MustRegister("advanced", colfeaturegate.StageBeta)
	colfeaturegate.GlobalRegistry().MustRegister("false", colfeaturegate.StageStable, colfeaturegate.WithRegisterRemovalVersion("v0.0.1"))

	// registers any flags that underlying libraries might use
	opts := zap.Options{}
	flagset := featuregate.Flags(colfeaturegate.GlobalRegistry())
	opts.BindFlags(flag.CommandLine)
	pflag.CommandLine.AddGoFlagSet(flag.CommandLine)
	pflag.CommandLine.AddGoFlagSet(flagset)

        ... 

}

❯ go run ./main.go --help 
Usage of /var/folders/kv/z8h_0xts4h7dcr7fl3jsfr540000gp/T/go-build2330073747/b001/exe/main:
      --auto-instrumentation-dotnet-image string   The default OpenTelemetry DotNet instrumentation image. This image is used when no image is specified in the CustomResource. (default "ghcr.io/open-telemetry/opentelemetry-operator/autoinstrumentation-dotnet:0.0.0")
      --auto-instrumentation-java-image string     The default OpenTelemetry Java instrumentation image. This image is used when no image is specified in the CustomResource. (default "ghcr.io/open-telemetry/opentelemetry-operator/autoinstrumentation-java:0.0.0")
      --auto-instrumentation-nodejs-image string   The default OpenTelemetry NodeJS instrumentation image. This image is used when no image is specified in the CustomResource. (default "ghcr.io/open-telemetry/opentelemetry-operator/autoinstrumentation-nodejs:0.0.0")
      --auto-instrumentation-python-image string   The default OpenTelemetry Python instrumentation image. This image is used when no image is specified in the CustomResource. (default "ghcr.io/open-telemetry/opentelemetry-operator/autoinstrumentation-python:0.0.0")
      --collector-image string                     The default OpenTelemetry collector image. This image is used when no image is specified in the CustomResource. (default "ghcr.io/open-telemetry/opentelemetry-collector-releases/opentelemetry-collector:0.0.0")
      --enable-leader-election                     Enable leader election for controller manager. Enabling this will ensure there is only one active controller manager.
      --feature-gates flag                         Comma-delimited list of feature gate identifiers. Prefix with '-' to disable the feature. '+' or no prefix will enable the feature. (default advanced,-basic,false)
      --health-probe-addr string                   The address the probe endpoint binds to. (default ":8081")
      --kubeconfig string                          Paths to a kubeconfig. Only required if out-of-cluster.
      --labels stringArray                         Labels to filter away from propagating onto deploys
      --metrics-addr string                        The address the metric endpoint binds to. (default ":8080")
      --operator-opamp-bridge-image string         The default OpenTelemetry Operator OpAMP Bridge image. This image is used when no image is specified in the CustomResource. (default "ghcr.io/open-telemetry/opentelemetry-operator/operator-opamp-bridge:0.0.0")
      --target-allocator-image string              The default OpenTelemetry target allocator image. This image is used when no image is specified in the CustomResource. (default "ghcr.io/open-telemetry/opentelemetry-operator/target-allocator:0.0.0")
      --tls-cipher-suites strings                  Comma-separated list of cipher suites for the server. Values are from tls package constants (https://golang.org/pkg/crypto/tls/#pkg-constants). If omitted, the default Go cipher suites will be used
      --tls-min-version string                     Minimum TLS version supported. Value must match version names from https://golang.org/pkg/crypto/tls/#pkg-constants. (default "VersionTLS12")
      --webhook-port int                           The port the webhook endpoint binds to. (default 9443)
      --zap-devel                                  Development Mode defaults(encoder=consoleEncoder,logLevel=Debug,stackTraceLevel=Warn). Production Mode defaults(encoder=jsonEncoder,logLevel=Info,stackTraceLevel=Error)
      --zap-encoder encoder                        Zap log encoding (one of 'json' or 'console')
      --zap-log-level level                        Zap Level to configure the verbosity of logging. Can be one of 'debug', 'info', 'error', or any integer value > 0 which corresponds to custom debug levels of increasing verbosity
      --zap-stacktrace-level level                 Zap Level at and above which stacktraces are captured (one of 'info', 'error', 'panic').
      --zap-time-encoding time-encoding            Zap time encoding (one of 'epoch', 'millis', 'nano', 'iso8601', 'rfc3339' or 'rfc3339nano'). Defaults to 'epoch'.
pflag: help requested
exit status 2

[jaronoff97]

@TylerHelmuth thank you for taking this on 🙇 vacation meant little working time for me :)