Expose performance options (#1083)

This allow admins to specify a few parameters to better suit their use
of Chains.

`--threads-per-controller` controls the number of concurrent threads the
Chains controller processes. The default value is 2.

`--kube-api-burst` controle the maximum burst for throttle.

`--kube-api-qps` controles the maximum QPS to the server from the
client.

The approach taken here is the same one used by the Tekton Pipeline
controller for the sake of consistency in the ecosystem.

Signed-off-by: Luiz Carvalho <lucarval@redhat.com>

cmd/controller/main.go

@@ -18,6 +18,10 @@ import (
 
 	"github.com/tektoncd/chains/pkg/reconciler/pipelinerun"
 	"github.com/tektoncd/chains/pkg/reconciler/taskrun"
+
+	"k8s.io/client-go/rest"
+
+	"knative.dev/pkg/controller"
 	"knative.dev/pkg/injection"
 	"knative.dev/pkg/injection/sharedmain"
 	"knative.dev/pkg/signals"
@@ -35,11 +39,22 @@ import (
 	_ "github.com/sigstore/sigstore/pkg/signature/kms/hashivault"
 )
 
-var namespace = flag.String("namespace", "", "Namespace to restrict informer to. Optional, defaults to all namespaces.")
-
 func main() {
+	flag.IntVar(&controller.DefaultThreadsPerController, "threads-per-controller", controller.DefaultThreadsPerController, "Threads (goroutines) to create per controller")
+	namespace := flag.String("namespace", "", "Namespace to restrict informer to. Optional, defaults to all namespaces.")
+
+	// This also calls flag.Parse().
+	cfg := injection.ParseAndGetRESTConfigOrDie()
+
+	if cfg.QPS == 0 {
+		cfg.QPS = 2 * rest.DefaultQPS
+	}
+	if cfg.Burst == 0 {
+		cfg.Burst = rest.DefaultBurst
+	}
+
 	flag.Parse()
 	ctx := injection.WithNamespaceScope(signals.NewContext(), *namespace)
 
-	sharedmain.MainWithContext(ctx, "watcher", taskrun.NewController, pipelinerun.NewController)
+	sharedmain.MainWithConfig(ctx, "watcher", cfg, taskrun.NewController, pipelinerun.NewController)
 }

docs/performance.md

@@ -0,0 +1,27 @@
+# Performance
+
+Tekton Chains exposes a few parameters that can be used to fine tune the controllers execution to
+improve its performance as needed.
+
+The controller accepts the following parameters:
+
+`--threads-per-controller` controls the number of concurrent threads the Chains controller
+processes. The default value is 2.
+
+`--kube-api-burst` controle the maximum burst for throttle. The default value is 10.
+
+`--kube-api-qps` controles the maximum QPS to the server from the client. The default value is 5.
+
+Modify the `Deployment` to use those parameters, for example:
+
+```yaml
+spec:
+    template:
+        spec:
+            containers:
+                - image: gcr.io/tekton-releases/github.com/tektoncd/chains/cmd/controller:v0.20.0
+                  args:
+                    - --threads-per-controller=32
+                    - --kube-api-burst=2
+                    - --kube-api-qps=3
+```