Add default provider and controller rate limiters

Adds default rate limiters to be used at both the provider and
controller level. The provider rate limiter is a configurable token
bucket and the controller limiter is a max of limiter that uses the
provider limiter and a per-item exponential backoff.

Signed-off-by: hasheddan <[email protected]>

pkg/ratelimiter/default.go

@@ -0,0 +1,48 @@
+/*
+Copyright 2021 The Crossplane 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 ratelimiter
+
+import (
+	"time"
+
+	"golang.org/x/time/rate"
+	"k8s.io/client-go/util/workqueue"
+	"sigs.k8s.io/controller-runtime/pkg/ratelimiter"
+)
+
+// DefaultProviderRPS is the recommended default average requeues per second
+// tolerated by a provider's controller manager.
+const DefaultProviderRPS = 1
+
+// NewDefaultProviderRateLimiter returns a token bucket rate limiter meant for
+// limiting the number of average total requeues per second for all controllers
+// registered with a controller manager. The bucket size is a linear function of
+// the requeues per second.
+func NewDefaultProviderRateLimiter(rps int) *workqueue.BucketRateLimiter {
+	return &workqueue.BucketRateLimiter{Limiter: rate.NewLimiter(rate.Limit(rps), rps*10)}
+}
+
+// NewDefaultManagedRateLimiter returns a rate limiter that takes the maximum
+// delay between the passed providerRateLimiter and a per-item exponential
+// backoff limiter. The exponential backoff limiter has a base delay of 1s and a
+// maximum of 60s.
+func NewDefaultManagedRateLimiter(providerRateLimiter ratelimiter.RateLimiter) ratelimiter.RateLimiter {
+	return workqueue.NewMaxOfRateLimiter(
+		workqueue.NewItemExponentialFailureRateLimiter(1*time.Second, 60*time.Second),
+		providerRateLimiter,
+	)
+}

pkg/ratelimiter/default_test.go

@@ -0,0 +1,42 @@
+/*
+Copyright 2021 The Crossplane 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 ratelimiter
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestDefaultMangedRateLimiter(t *testing.T) {
+	limiter := NewDefaultManagedRateLimiter(NewDefaultProviderRateLimiter(DefaultProviderRPS))
+	backoffSchedule := []int{1, 2, 4, 8, 16, 32, 60}
+	for _, d := range backoffSchedule {
+		if e, a := time.Duration(d)*time.Second, limiter.When("one"); e != a {
+			t.Errorf("expected %v, got %v", e, a)
+		}
+	}
+	limiter.Forget("one")
+	if e, a := time.Duration(backoffSchedule[0])*time.Second, limiter.When("one"); e != a {
+		t.Errorf("expected %v, got %v", e, a)
+	}
+	wg := &sync.WaitGroup{}
+	wg.Add(1)
+	go func() {
+		wg.Done()
+	}()
+}