fix(#951): add exception for self-hosted label in webhook search (#953)

The webhook "workflowJob" pass the labels the job needs to the controller, who in turns search for them in its RunnerDeployment / RunnerSet. The current implementation ignore the search for `self-hosted` if this is the only label, however if multiple labels are found the `self-hosted` label must be declared explicitely or the RD / RS will not be selected for the autoscaling.

This PR fixes the behavior by ignoring this label, and add documentation on this webhook for the other labels that will still require an explicit declaration (OS and architecture). 

The exception should be temporary, ideally the labels implicitely created (self-hosted, OS, architecture) should be searchable alongside the explicitly declared labels.

code tested, work with `["self-hosted"]` and `["self-hosted","anotherLabel"]`

Fixes #951

README.md

@@ -615,6 +615,8 @@ spec:
     duration: "30m"
 ```
 
+This webhook requires you to explicitely set the labels in the RunnerDeployment / RunnerSet if you are using them in your workflow to match the agents (field `runs-on`). Only `self-hosted` will be considered as included by default.
+
 You can configure your GitHub webhook settings to only include `Workflows Job` events, so that it sends us three kinds of `workflow_job` events per a job run.
 
 Each kind has a `status` of `queued`, `in_progress` and `completed`. With the above configuration, `actions-runner-controller` adds one runner for a `workflow_job` event whose `status` is `queued`. Similarly, it removes one runner for a `workflow_job` event whose `status` is `completed`. The cavaet to this to remember is that this the scale down is within the bounds of your `scaleDownDelaySecondsAfterScaleOut` configuration, if this time hasn't past the scale down will be defered.

controllers/horizontal_runner_autoscaler_webhook.go

@@ -580,13 +580,17 @@ HRA:
 				return nil, err
 			}
 
-			if len(labels) == 1 && labels[0] == "self-hosted" {
-				return &ScaleTarget{HorizontalRunnerAutoscaler: hra, ScaleUpTrigger: v1alpha1.ScaleUpTrigger{Duration: duration}}, nil
-			}
-
 			// Ensure that the RunnerSet-managed runners have all the labels requested by the workflow_job.
 			for _, l := range labels {
 				var matched bool
+
+				// ignore "self-hosted" label as all instance here are self-hosted
+				if l == "self-hosted" {
+					continue
+				}
+
+				// TODO labels related to OS and architecture needs to be explicitely declared or the current implementation will not be able to find them.
+
 				for _, l2 := range rs.Spec.Labels {
 					if l == l2 {
 						matched = true
@@ -607,13 +611,17 @@ HRA:
 				return nil, err
 			}
 
-			if len(labels) == 1 && labels[0] == "self-hosted" {
-				return &ScaleTarget{HorizontalRunnerAutoscaler: hra, ScaleUpTrigger: v1alpha1.ScaleUpTrigger{Duration: duration}}, nil
-			}
-
 			// Ensure that the RunnerDeployment-managed runners have all the labels requested by the workflow_job.
 			for _, l := range labels {
 				var matched bool
+
+				// ignore "self-hosted" label as all instance here are self-hosted
+				if l == "self-hosted" {
+					continue
+				}
+
+				// TODO labels related to OS and architecture needs to be explicitely declared or the current implementation will not be able to find them.
+
 				for _, l2 := range rd.Spec.Template.Spec.Labels {
 					if l == l2 {
 						matched = true