Add git-optimized-clones feature gate

OptimizedGitClones decreases resource utilization for GitRepository
reconciliations. It supports both go-git and libgit2 implementations
when cloning repositories using branches or tags.

This is an opt-out feature, which can be disabled by starting the
controller with the argument '--feature-gates=OptimizedGitClones=false'.

Signed-off-by: Paulo Gomes <paulo.gomes@weave.works>

controllers/gitrepository_controller.go

@@ -48,6 +48,7 @@ import (
 
 	sourcev1 "github.com/fluxcd/source-controller/api/v1beta2"
 	serror "github.com/fluxcd/source-controller/internal/error"
+	"github.com/fluxcd/source-controller/internal/features"
 	sreconcile "github.com/fluxcd/source-controller/internal/reconcile"
 	"github.com/fluxcd/source-controller/internal/reconcile/summarize"
 	"github.com/fluxcd/source-controller/internal/util"
@@ -413,8 +414,10 @@ func (r *GitRepositoryReconciler) reconcileSource(ctx context.Context,
 		checkoutOpts.SemVer = ref.SemVer
 	}
 
-	if artifact := obj.GetArtifact(); artifact != nil {
+	if oc, _ := features.Enabled(features.OptimizedGitClones); oc {
-		checkoutOpts.LastRevision = artifact.Revision
+		if artifact := obj.GetArtifact(); artifact != nil {
+			checkoutOpts.LastRevision = artifact.Revision
+		}
 	}
 
 	checkoutStrategy, err := strategy.CheckoutStrategyForImplementation(ctx,
@@ -464,7 +467,7 @@ func (r *GitRepositoryReconciler) reconcileSource(ctx context.Context,
 		var v git.NoChangesError
 		if errors.As(err, &v) {
 			return sreconcile.ResultSuccess,
-				&serror.Waiting{Err: v, Reason: v.Message}
+				&serror.Waiting{Err: v, Reason: v.Message, RequeueAfter: obj.GetRequeueAfter()}
 		}
 
 		e := &serror.Event{

docs/spec/v1beta2/gitrepositories.md

@@ -399,6 +399,22 @@ transport being handled by the controller, instead of `libgit2`.
 This may lead to an increased number of timeout messages in the logs, however
 it will fix the bug in which Git operations make the controllers hang indefinitely.
 
+#### Optimized Git clones
+
+Optimized Git clones decreases resource utilization for GitRepository
+reconciliations. It supports both `go-git` and `libgit2` implementations
+when cloning repositories using branches or tags.
+
+When enabled, avoids full clone operations by first checking whether
+the last revision is still the same at the target repository,
+and if that is so, skips the reconciliation.
+
+This feature is enabled by default. It can be disabled by starting the
+controller with the argument `--feature-gates=OptimizedGitClones=false`.
+
+NB: GitRepository objects configured for SemVer or Commit clones are
+not affected by this functionality.
+
 #### Proxy support
 
 When a proxy is configured in the source-controller Pod through the appropriate

go.mod

@@ -25,7 +25,7 @@ require (
 	github.com/fluxcd/pkg/gitutil v0.1.0
 	github.com/fluxcd/pkg/helmtestserver v0.7.2
 	github.com/fluxcd/pkg/lockedfile v0.1.0
-	github.com/fluxcd/pkg/runtime v0.14.2
+	github.com/fluxcd/pkg/runtime v0.15.1
 	github.com/fluxcd/pkg/ssh v0.3.3
 	github.com/fluxcd/pkg/testserver v0.2.0
 	github.com/fluxcd/pkg/untar v0.1.0
@@ -185,7 +185,7 @@ require (
 	github.com/shopspring/decimal v1.2.0 // indirect
 	github.com/sirupsen/logrus v1.8.1 // indirect
 	github.com/spf13/cast v1.4.1 // indirect
-	github.com/spf13/cobra v1.3.0 // indirect
+	github.com/spf13/cobra v1.4.0 // indirect
 	github.com/stretchr/testify v1.7.1 // indirect
 	github.com/xanzy/ssh-agent v0.3.1 // indirect
 	github.com/xeipuuv/gojsonpointer v0.0.0-20180127040702-4e3ac2762d5f // indirect

go.sum

@@ -364,8 +364,8 @@ github.com/fluxcd/pkg/helmtestserver v0.7.2/go.mod h1:WtUXBrfpJdwK54LX1Tqd8PpLJY
 github.com/fluxcd/pkg/lockedfile v0.1.0 h1:YsYFAkd6wawMCcD74ikadAKXA4s2sukdxrn7w8RB5eo=
 github.com/fluxcd/pkg/lockedfile v0.1.0/go.mod h1:EJLan8t9MiOcgTs8+puDjbE6I/KAfHbdvIy9VUgIjm8=
 github.com/fluxcd/pkg/runtime v0.13.0-rc.6/go.mod h1:4oKUO19TeudXrnCRnxCfMSS7EQTYpYlgfXwlQuDJ/Eg=
-github.com/fluxcd/pkg/runtime v0.14.2 h1:ktyUjcX4pHoC8DRoBmhEP6eMHbmR6+/MYoARe4YulZY=
+github.com/fluxcd/pkg/runtime v0.15.1 h1:PKooYqlZM+KLhnNz10sQnBH0AHllS40PIDHtiRH/BGU=
-github.com/fluxcd/pkg/runtime v0.14.2/go.mod h1:NZr3PRK7xX2M1bl0LdtugvQyWkOmu2NcW3NrZH6U0is=
+github.com/fluxcd/pkg/runtime v0.15.1/go.mod h1:TPAoOEgUFG60FXBA4ID41uaPldxuXCEI4jt3qfd5i5Q=
 github.com/fluxcd/pkg/ssh v0.3.3 h1:/tc7W7LO1VoVUI5jB+p9ZHCA+iQaXTkaSCDZJsxcZ9k=
 github.com/fluxcd/pkg/ssh v0.3.3/go.mod h1:+bKhuv0/pJy3HZwkK54Shz68sNv1uf5aI6wtPaEHaYk=
 github.com/fluxcd/pkg/testserver v0.2.0 h1:Mj0TapmKaywI6Fi5wvt1LAZpakUHmtzWQpJNKQ0Krt4=
@@ -990,8 +990,9 @@ github.com/spf13/cobra v0.0.6/go.mod h1:/6GTrnGXV9HjY+aR4k0oJ5tcvakLuG6EuKReYlHN
 github.com/spf13/cobra v1.0.0/go.mod h1:/6GTrnGXV9HjY+aR4k0oJ5tcvakLuG6EuKReYlHNrgE=
 github.com/spf13/cobra v1.1.3/go.mod h1:pGADOWyqRD/YMrPZigI/zbliZ2wVD/23d+is3pSWzOo=
 github.com/spf13/cobra v1.2.1/go.mod h1:ExllRjgxM/piMAM+3tAZvg8fsklGAf3tPfi+i8t68Nk=
-github.com/spf13/cobra v1.3.0 h1:R7cSvGu+Vv+qX0gW5R/85dx2kmmJT5z5NM8ifdYjdn0=
 github.com/spf13/cobra v1.3.0/go.mod h1:BrRVncBjOJa/eUcVVm9CE+oC6as8k+VYr4NY7WCi9V4=
+github.com/spf13/cobra v1.4.0 h1:y+wJpx64xcgO1V+RcnwW0LEHxTKRi2ZDPSBjWnrg88Q=
+github.com/spf13/cobra v1.4.0/go.mod h1:Wo4iy3BUC+X2Fybo0PDqwJIv3dNRiZLHQymsfxlB84g=
 github.com/spf13/jwalterweatherman v1.0.0/go.mod h1:cQK4TGJAtQXfYWX+Ddv3mKDzgVb68N+wFjFa4jdeBTo=
 github.com/spf13/jwalterweatherman v1.1.0/go.mod h1:aNWZUN0dPAAO/Ljvb5BEdw96iTZ0EXowPYD95IqWIGo=
 github.com/spf13/pflag v0.0.0-20170130214245-9ff6c6923cff/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=

internal/features/features.go

@@ -0,0 +1,54 @@
+/*
+Copyright 2022 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package features sets the feature gates that
+// source-controller supports, and their default
+// states.
+package features
+
+import feathelper "github.com/fluxcd/pkg/runtime/features"
+
+const (
+	// OptimizedGitClones decreases resource utilization for GitRepository
+	// reconciliations. It supports both go-git and libgit2 implementations
+	// when cloning repositories using branches or tags.
+	//
+	// When enabled, avoids full clone operations by first checking whether
+	// the last revision is still the same at the target repository,
+	// and if that is so, skips the reconciliation.
+	OptimizedGitClones = "OptimizedGitClones"
+)
+
+var features = map[string]bool{
+	// OptimizedGitClones
+	// opt-out from v0.25
+	OptimizedGitClones: true,
+}
+
+// DefaultFeatureGates contains a list of all supported feature gates and
+// their default values.
+func FeatureGates() map[string]bool {
+	return features
+}
+
+// Enabled verifies whether the feature is enabled or not.
+//
+// This is only a wrapper around the Enabled func in
+// pkg/runtime/features, so callers won't need to import
+// both packages for checking whether a feature is enabled.
+func Enabled(feature string) (bool, error) {
+	return feathelper.Enabled(feature)
+}

main.go

@@ -36,10 +36,12 @@ import (
 	"github.com/fluxcd/pkg/runtime/client"
 	helper "github.com/fluxcd/pkg/runtime/controller"
 	"github.com/fluxcd/pkg/runtime/events"
+	feathelper "github.com/fluxcd/pkg/runtime/features"
 	"github.com/fluxcd/pkg/runtime/leaderelection"
 	"github.com/fluxcd/pkg/runtime/logger"
 	"github.com/fluxcd/pkg/runtime/pprof"
 	"github.com/fluxcd/pkg/runtime/probes"
+	"github.com/fluxcd/source-controller/internal/features"
 
 	sourcev1 "github.com/fluxcd/source-controller/api/v1beta2"
 	"github.com/fluxcd/source-controller/controllers"
@@ -88,6 +90,7 @@ func main() {
 		logOptions               logger.Options
 		leaderElectionOptions    leaderelection.Options
 		rateLimiterOptions       helper.RateLimiterOptions
+		featureGates             feathelper.FeatureGates
 		helmCacheMaxSize         int
 		helmCacheTTL             string
 		helmCachePurgeInterval   string
@@ -136,11 +139,20 @@ func main() {
 	logOptions.BindFlags(flag.CommandLine)
 	leaderElectionOptions.BindFlags(flag.CommandLine)
 	rateLimiterOptions.BindFlags(flag.CommandLine)
+	featureGates.BindFlags(flag.CommandLine)
 
 	flag.Parse()
 
 	ctrl.SetLogger(logger.NewLogger(logOptions))
 
+	err := featureGates.WithLogger(setupLog).
+		SupportedFeatures(features.FeatureGates())
+
+	if err != nil {
+		setupLog.Error(err, "unable to load feature gates")
+		os.Exit(1)
+	}
+
 	// Set upper bound file size limits Helm
 	helm.MaxIndexSize = helmIndexLimit
 	helm.MaxChartSize = helmChartLimit