cmd/contour: optional CRDs (projectcontour#5080) (projectcontour#5080)

Allow disabling certain informers for CRDs by passing a
command line flag to the serve command. This makes the
corresponding CRD effectively optional.

Fixes projectcontour#4684

Signed-off-by: Niklas Simons <niklas.simons@est.tech>

changelogs/unreleased/5080-nsimons-minor.md

@@ -0,0 +1,8 @@
+## Allow Disabling Features
+
+The `contour serve` command takes a new optional flag, `--disable-feature`, that allows disabling
+certain features.
+
+Currently this flag can be used to disable the informer for ExtensionService resources,
+effectively making the ExtensionService CRD optional in the cluster.
+To do this, use the flag as follows: `--disable-feature=extensionservices`

cmd/contour/serve.go

@@ -126,6 +126,7 @@ func registerServe(app *kingpin.Application) (*kingpin.CmdClause, *serveContext)
 	serve.Flag("debug", "Enable debug logging.").Short('d').BoolVar(&ctx.Config.Debug)
 	serve.Flag("debug-http-address", "Address the debug http endpoint will bind to.").PlaceHolder("<ipaddr>").StringVar(&ctx.debugAddr)
 	serve.Flag("debug-http-port", "Port the debug http endpoint will bind to.").PlaceHolder("<port>").IntVar(&ctx.debugPort)
+	serve.Flag("disable-feature", "Do not start an informer for the specified resources.").PlaceHolder("<extensionservices>").EnumsVar(&ctx.disabledFeatures, "extensionservices")
 	serve.Flag("disable-leader-election", "Disable leader election mechanism.").BoolVar(&ctx.LeaderElection.Disable)
 
 	serve.Flag("envoy-http-access-log", "Envoy HTTP access log.").PlaceHolder("/path/to/file").StringVar(&ctx.httpAccessLog)
@@ -469,15 +470,23 @@ func (s *Server) doServe() error {
 		Counter: contourMetrics.EventHandlerOperations,
 	}
 
-	// Inform on default resources.
-	for name, r := range map[string]client.Object{
+	// Start to build informers.
+	informerResources := map[string]client.Object{
 		"httpproxies":               &contour_api_v1.HTTPProxy{},
 		"tlscertificatedelegations": &contour_api_v1.TLSCertificateDelegation{},
 		"extensionservices":         &contour_api_v1alpha1.ExtensionService{},
 		"contourconfigurations":     &contour_api_v1alpha1.ContourConfiguration{},
 		"services":                  &corev1.Service{},
 		"ingresses":                 &networking_v1.Ingress{},
-	} {
+	}
+
+	// Some of the resources are optional and can be disabled, do not create informers for those.
+	for _, feat := range s.ctx.disabledFeatures {
+		delete(informerResources, feat)
+	}
+
+	// Inform on the remaining resources.
+	for name, r := range informerResources {
 		if err := informOnResource(r, eventHandler, s.mgr.GetCache()); err != nil {
 			s.log.WithError(err).WithField("resource", name).Fatal("failed to create informer")
 		}

cmd/contour/servecontext.go

@@ -87,6 +87,9 @@ type serveContext struct {
 
 	// Leader election configuration.
 	LeaderElection LeaderElection
+
+	// Features disabled by the user.
+	disabledFeatures []string
 }
 
 type ServerConfig struct {

site/content/docs/main/configuration.md

@@ -50,6 +50,7 @@ Many of these flags are mirrored in the [Contour Configuration File](#configurat
 | `--use-proxy-protocol`                                   | Use PROXY protocol for all listeners                                   |
 | `--accesslog-format=<envoy\|json>`                       | Format for Envoy access logs                                           |
 | `--disable-leader-election`                              | Disable leader election mechanism                                      |
+| `--disable-feature=<extensionservices>`                  | Do not start an informer for the specified resources.                  |
 | `--leader-election-lease-duration`                       | The duration of the leadership lease.                                  |
 | `--leader-election-renew-deadline`                       | The duration leader will retry refreshing leadership before giving up. |
 | `--leader-election-retry-period`                         | The interval which Contour will attempt to acquire leadership lease.   |

site/content/docs/main/deploy-options.md

@@ -201,6 +201,12 @@ Next, pass `--envoy-service-http-port=80 --envoy-service-https-port=443` to the
 This is best paired with a DaemonSet (perhaps paired with Node affinity) to ensure that a single instance of Contour runs on each Node.
 See the [AWS NLB tutorial][10] as an example.
 
+## Disabling Features
+
+You can run Contour with certain features disabled by passing `--disable-feature` flag to the Contour `serve` command.
+Currently this flag can be used to disable the informer for ExtensionService resources, effectively making the ExtensionService CRD optional in the cluster.
+To do this, use the flag as follows: `--disable-feature=extensionservices`
+
 ## Upgrading Contour/Envoy
 
 At times, it's needed to upgrade Contour, the version of Envoy, or both.