reverseproxy: Remove circuitbreaker module (see #3331)

Moving to https://github.com/caddyserver/circuitbreaker

Nobody was using it anyway -- it works well, but something got fumbled
in a refactoring *months* ago. Turns out that we forgot the interface
guards AND botched a method name (my bad) - Ok() should have been OK().
So it would always have thrown a runtime panic if it tried to be loaded.
The module itself works well, but obviously nobody used it because
nobody reported the error. Fixing this while we move it to the new repo.

Removing this removes the last Bazaar/Launchpad dependency (I think).

2 files changed, 2 insertions, 158 deletions

diff --git a/modules/caddyhttp/reverseproxy/circuitbreaker.go b/modules/caddyhttp/reverseproxy/circuitbreaker.go
deleted file mode 100644
index 830ab43..0000000
--- a/modules/caddyhttp/reverseproxy/circuitbreaker.go
+++ /dev/null
@@ -1,157 +0,0 @@
-// Copyright 2015 Matthew Holt and The Caddy 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 reverseproxy
-
-import (
-	"fmt"
-	"sync/atomic"
-	"time"
-
-	"github.com/caddyserver/caddy/v2"
-	"github.com/vulcand/oxy/memmetrics"
-)
-
-func init() {
-	caddy.RegisterModule(internalCircuitBreaker{})
-}
-
-// internalCircuitBreaker implements circuit breaking functionality
-// for requests within this process over a sliding time window.
-type internalCircuitBreaker struct {
-	tripped   int32
-	cbFactor  int32
-	threshold float64
-	metrics   *memmetrics.RTMetrics
-	tripTime  time.Duration
-	Config
-}
-
-// CaddyModule returns the Caddy module information.
-func (internalCircuitBreaker) CaddyModule() caddy.ModuleInfo {
-	return caddy.ModuleInfo{
-		ID:  "http.reverse_proxy.circuit_breakers.internal",
-		New: func() caddy.Module { return new(internalCircuitBreaker) },
-	}
-}
-
-// Provision sets up a configured circuit breaker.
-func (c *internalCircuitBreaker) Provision(ctx caddy.Context) error {
-	f, ok := typeCB[c.Factor]
-	if !ok {
-		return fmt.Errorf("type is not defined")
-	}
-
-	if c.TripTime == "" {
-		c.TripTime = defaultTripTime
-	}
-
-	tw, err := time.ParseDuration(c.TripTime)
-	if err != nil {
-		return fmt.Errorf("cannot parse trip_time duration, %v", err.Error())
-	}
-
-	mt, err := memmetrics.NewRTMetrics()
-	if err != nil {
-		return fmt.Errorf("cannot create new metrics: %v", err.Error())
-	}
-
-	c.cbFactor = f
-	c.tripTime = tw
-	c.threshold = c.Threshold
-	c.metrics = mt
-	c.tripped = 0
-
-	return nil
-}
-
-// Ok returns whether the circuit breaker is tripped or not.
-func (c *internalCircuitBreaker) Ok() bool {
-	tripped := atomic.LoadInt32(&c.tripped)
-	return tripped == 0
-}
-
-// RecordMetric records a response status code and execution time of a request. This function should be run in a separate goroutine.
-func (c *internalCircuitBreaker) RecordMetric(statusCode int, latency time.Duration) {
-	c.metrics.Record(statusCode, latency)
-	c.checkAndSet()
-}
-
-// Ok checks our metrics to see if we should trip our circuit breaker, or if the fallback duration has completed.
-func (c *internalCircuitBreaker) checkAndSet() {
-	var isTripped bool
-
-	switch c.cbFactor {
-	case factorErrorRatio:
-		// check if amount of network errors exceed threshold over sliding window, threshold for comparison should be < 1.0 i.e. .5 = 50th percentile
-		if c.metrics.NetworkErrorRatio() > c.threshold {
-			isTripped = true
-		}
-	case factorLatency:
-		// check if threshold in milliseconds is reached and trip
-		hist, err := c.metrics.LatencyHistogram()
-		if err != nil {
-			return
-		}
-
-		l := hist.LatencyAtQuantile(c.threshold)
-		if l.Nanoseconds()/int64(time.Millisecond) > int64(c.threshold) {
-			isTripped = true
-		}
-	case factorStatusCodeRatio:
-		// check ratio of error status codes of sliding window, threshold for comparison should be < 1.0 i.e. .5 = 50th percentile
-		if c.metrics.ResponseCodeRatio(500, 600, 0, 600) > c.threshold {
-			isTripped = true
-		}
-	}
-
-	if isTripped {
-		c.metrics.Reset()
-		atomic.AddInt32(&c.tripped, 1)
-
-		// wait tripTime amount before allowing operations to resume.
-		t := time.NewTimer(c.tripTime)
-		<-t.C
-
-		atomic.AddInt32(&c.tripped, -1)
-	}
-}
-
-// Config represents the configuration of a circuit breaker.
-type Config struct {
-	// The threshold over sliding window that would trip the circuit breaker
-	Threshold float64 `json:"threshold"`
-	// Possible values: latency, error_ratio, and status_ratio. It
-	// defaults to latency.
-	Factor string `json:"factor"`
-	// How long to wait after the circuit is tripped before allowing operations to resume.
-	// The default is 5s.
-	TripTime string `json:"trip_time"`
-}
-
-const (
-	factorLatency = iota + 1
-	factorErrorRatio
-	factorStatusCodeRatio
-	defaultTripTime = "5s"
-)
-
-var (
-	// typeCB handles converting a Config Factor value to the internal circuit breaker types.
-	typeCB = map[string]int32{
-		"latency":      factorLatency,
-		"error_ratio":  factorErrorRatio,
-		"status_ratio": factorStatusCodeRatio,
-	}
-)
diff --git a/modules/caddyhttp/reverseproxy/healthchecks.go b/modules/caddyhttp/reverseproxy/healthchecks.go
index 85274c6..02d8438 100644
--- a/modules/caddyhttp/reverseproxy/healthchecks.go
+++ b/modules/caddyhttp/reverseproxy/healthchecks.go
@@ -113,7 +113,8 @@ type PassiveHealthChecks struct {
 
 // CircuitBreaker is a type that can act as an early-warning
 // system for the health checker when backends are getting
-// overloaded.
+// overloaded. This interface is still experimental and is
+// subject to change.
 type CircuitBreaker interface {
 	OK() bool
 	RecordMetric(statusCode int, latency time.Duration)