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Edward 2020-05-08 16:16:04 +08:00
parent 9cb8114cce
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@ -6,7 +6,7 @@ wires to heat up and combust, the circuit breaker design pattern is a fail-first
mechanism that shuts down the circuit, request/response relationship or a mechanism that shuts down the circuit, request/response relationship or a
service in the case of software development, to prevent bigger failures. service in the case of software development, to prevent bigger failures.
**Note:** The words "circuit" and "service" are used synonymously throught this **Note:** The words "circuit" and "service" are used synonymously through this
document. document.
## Implementation ## Implementation
@ -24,22 +24,22 @@ failures.
package circuit package circuit
import ( import (
"time" "time"
) )
type State int type State int
const ( const (
UnknownState State = iota UnknownState State = iota
FailureState FailureState
SuccessState SuccessState
) )
type Counter interface { type Counter interface {
Count(State) Count(State)
ConsecutiveFailures() uint32 ConsecutiveFailures() uint32
LastActivity() time.Time LastActivity() time.Time
Reset() Reset()
} }
``` ```
@ -49,51 +49,51 @@ Circuit is wrapped using the `circuit.Breaker` closure that keeps an internal op
It returns a fast error if the circuit has failed consecutively more than the specified threshold. It returns a fast error if the circuit has failed consecutively more than the specified threshold.
After a while it retries the request and records it. After a while it retries the request and records it.
**Note:** Context type is used here to carry deadlines, cancelation signals, and **Note:** Context type is used here to carry deadlines, cancellation signals, and
other request-scoped values across API boundaries and between processes. other request-scoped values across API boundaries and between processes.
```go ```go
package circuit package circuit
import ( import (
"context" "context"
"time" "time"
) )
type Circuit func(context.Context) error type Circuit func(context.Context) error
func Breaker(c Circuit, failureThreshold uint32) Circuit { func Breaker(c Circuit, failureThreshold uint32) Circuit {
cnt := NewCounter() cnt := NewCounter()
return func(ctx context) error { return func(ctx context) error {
if cnt.ConsecutiveFailures() >= failureThreshold { if cnt.ConsecutiveFailures() >= failureThreshold {
canRetry := func(cnt Counter) { canRetry := func(cnt Counter) {
backoffLevel := Cnt.ConsecutiveFailures() - failureThreshold backOffLevel := Cnt.ConsecutiveFailures() - failureThreshold
// Calculates when should the circuit breaker resume propagating requests // Calculates when should the circuit breaker resume propagating requests
// to the service // to the service
shouldRetryAt := cnt.LastActivity().Add(time.Seconds * 2 << backoffLevel) shouldRetryAt := cnt.LastActivity().Add(time.Seconds * 2 << backOffLevel)
return time.Now().After(shouldRetryAt) return time.Now().After(shouldRetryAt)
} }
if !canRetry(cnt) { if !canRetry(cnt) {
// Fails fast instead of propagating requests to the circuit since // Fails fast instead of propagating requests to the circuit since
// not enough time has passed since the last failure to retry // not enough time has passed since the last failure to retry
return ErrServiceUnavailable return ErrServiceUnavailable
} }
} }
// Unless the failure threshold is exceeded the wrapped service mimics the // Unless the failure threshold is exceeded the wrapped service mimics the
// old behavior and the difference in behavior is seen after consecutive failures // old behavior and the difference in behavior is seen after consecutive failures
if err := c(ctx); err != nil { if err := c(ctx); err != nil {
cnt.Count(FailureState) cnt.Count(FailureState)
return err return err
} }
cnt.Count(SuccessState) cnt.Count(SuccessState)
return nil return nil
} }
} }
``` ```