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author | Matthew Holt <mholt@users.noreply.github.com> | 2019-10-09 19:28:07 -0600 |
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committer | Matthew Holt <mholt@users.noreply.github.com> | 2019-10-09 19:28:07 -0600 |
commit | bcbe1c220de99146a13bcc786ec7f5017681de73 (patch) | |
tree | 0d61a7327018a39294e8346d1751f2bd3ffd8674 | |
parent | a53b27c62e792e09380876db916289c77f2ae2e0 (diff) |
reverse_proxy: Add local circuit breaker
This migrates a feature that was previously reserved for enterprise
users, according to https://github.com/caddyserver/caddy/issues/2786.
The local circuit breaker is a simple metrics counter that can cause
the reverse proxy to consider a backend unhealthy before it actually
goes offline, by measuring recent latencies over a sliding window.
Credit to Danny Navarro
-rw-r--r-- | modules/caddyhttp/reverseproxy/circuitbreaker.go | 152 |
1 files changed, 152 insertions, 0 deletions
diff --git a/modules/caddyhttp/reverseproxy/circuitbreaker.go b/modules/caddyhttp/reverseproxy/circuitbreaker.go new file mode 100644 index 0000000..de2a6f9 --- /dev/null +++ b/modules/caddyhttp/reverseproxy/circuitbreaker.go @@ -0,0 +1,152 @@ +// 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(localCircuitBreaker{}) +} + +// localCircuitBreaker implements circuit breaking functionality +// for requests within this process over a sliding time window. +type localCircuitBreaker struct { + tripped int32 + cbType int32 + threshold float64 + metrics *memmetrics.RTMetrics + tripTime time.Duration + Config +} + +// CaddyModule returns the Caddy module information. +func (localCircuitBreaker) CaddyModule() caddy.ModuleInfo { + return caddy.ModuleInfo{ + Name: "http.handlers.reverse_proxy.circuit_breakers.local", + New: func() caddy.Module { return new(localCircuitBreaker) }, + } +} + +// Provision sets up a configured circuit breaker. +func (c *localCircuitBreaker) Provision(ctx caddy.Context) error { + t, ok := typeCB[c.Type] + 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.cbType = t + 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 *localCircuitBreaker) 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 *localCircuitBreaker) 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 *localCircuitBreaker) checkAndSet() { + var isTripped bool + + switch c.cbType { + case typeErrorRatio: + // 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 typeLatency: + // 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 typeStatusCodeRatio: + // 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 { + Threshold float64 `json:"threshold"` + Type string `json:"type"` + TripTime string `json:"trip_time"` +} + +const ( + typeLatency = iota + 1 + typeErrorRatio + typeStatusCodeRatio + defaultTripTime = "5s" +) + +var ( + // typeCB handles converting a Config Type value to the internal circuit breaker types. + typeCB = map[string]int32{ + "latency": typeLatency, + "error_ratio": typeErrorRatio, + "status_ratio": typeStatusCodeRatio, + } +) |