2.9 KiB
Circuit Breaker Pattern
Similar to electrical fuses that prevent fires when a circuit that is connected to the electrical grid starts drawing a high amount of power which causes the 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 service in the case of software development, to prevent bigger failures.
Note: The words "circuit" and "service" are used synonymously through this document.
Implementation
Below is the implementation of a very simple circuit breaker to illustrate the purpose of the circuit breaker design pattern for Circuit Breaker Pattern
Operation Counter
circuit.Counter is a simple counter that records success and failure states of
a circuit along with a timestamp and calculates the consecutive number of
failures.
package circuit
import (
"time"
)
type State int
const (
UnknownState State = iota
FailureState
SuccessState
)
type Counter interface {
Count(State)
ConsecutiveFailures() uint32
LastActivity() time.Time
Reset()
}
Circuit Breaker
Circuit is wrapped using the circuit.Breaker closure that keeps an internal operation counter.
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.
Note: Context type is used here to carry deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes.
package circuit
import (
"context"
"time"
)
type Circuit func(context.Context) error
func Breaker(c Circuit, failureThreshold uint32) Circuit {
cnt := NewCounter()
expired := time.Now()
currentState := StateClosed
return func(ctx context.Context) error {
//handle statue transformation for timeout
if currentState == StateOpen {
nowt := time.Now()
if expired.Before(nowt) || expired.Equal(nowt) {
currentState = StateHalfOpen
cnt.ConsecutiveSuccesses = 0
}
}
switch currentState {
case StateOpen:
return ErrServiceUnavailable
case StateHalfOpen:
if err := c(ctx); err != nil {
currentState = StateOpen
expired = time.Now().Add(defaultTimeout) //Reset
return err
}
cnt.Count(SuccessState)
if cnt.ConsecutiveSuccesses > defaultSuccessThreshold {
currentState = StateClosed
cnt.ConsecutiveFailures = 0
}
case StateClosed:
if err := c(ctx); err != nil {
cnt.Count(FailureState)
}
}
return nil
}
}
Related Contents
-
sony/gobreaker is a well-tested and intuitive circuit breaker implementation for real-world use cases.