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