gobreaker

gobreaker implements the Circuit Breaker pattern in Go.

Installation

go get github.com/sony/gobreaker

Usage

The struct CircuitBreaker is a state machine to prevent sending requests that are likely to fail. The function NewCircuitBreaker creates a new CircuitBreaker.

func NewCircuitBreaker(st Settings) *CircuitBreaker

You can configure CircuitBreaker by the struct Settings:

type Settings struct {
	Name          string
	MaxRequests   uint32
	Interval      time.Duration
	Timeout       time.Duration
	ReadyToTrip   func(counts Counts) bool
	RecordError   func(err error) bool
	OnStateChange func(name string, from State, to State)
}

• Name is the name of the CircuitBreaker.

• MaxRequests is the maximum number of requests allowed to pass through when the CircuitBreaker is half-open. If MaxRequests is 0, CircuitBreaker allows only 1 request.

• Interval is the cyclic period of the closed state for CircuitBreaker to clear the internal Counts, described later in this section. If Interval is 0, CircuitBreaker doesn't clear the internal Counts during the closed state.

• Timeout is the period of the open state, after which the state of CircuitBreaker becomes half-open. If Timeout is 0, the timeout value of CircuitBreaker is set to 60 seconds.

• ReadyToTrip is called with a copy of Counts whenever a request fails in the closed state. If ReadyToTrip returns true, CircuitBreaker will be placed into the open state. If ReadyToTrip is nil, default ReadyToTrip is used. Default ReadyToTrip returns true when the number of consecutive failures is more than 5.

• RecordError is called when a non-nil error is returned by the function, and intends to differentiate errors that should be used for tripping the circuit or not. If RecordError returns true, CircuitBreaker will consider the error should be recorded, so the operation will be marked as unsuccessful If RecordError returns false, CircuitBreaker will consider the error should not be recorded, so the operation will be marked as successful If RecordError is nil, default RecordError is used. Default RecordError considers all errors should be recorded

• OnStateChange is called whenever the state of CircuitBreaker changes.

The struct Counts holds the numbers of requests and their successes/failures:

type Counts struct {
	Requests             uint32
	TotalSuccesses       uint32
	TotalFailures        uint32
	ConsecutiveSuccesses uint32
	ConsecutiveFailures  uint32
}

CircuitBreaker clears the internal Counts either on the change of the state or at the closed-state intervals. Counts ignores the results of the requests sent before clearing.

CircuitBreaker can wrap any function to send a request:

func (cb *CircuitBreaker) Execute(req func() (interface{}, error)) (interface{}, error)

The method Execute runs the given request if CircuitBreaker accepts it. Execute returns an error instantly if CircuitBreaker rejects the request. Otherwise, Execute returns the result of the request. If a panic occurs in the request, CircuitBreaker handles it as an error and causes the same panic again.

Example

var cb *breaker.CircuitBreaker

func Get(url string) ([]byte, error) {
	body, err := cb.Execute(func() (interface{}, error) {
		resp, err := http.Get(url)
		if err != nil {
			return nil, err
		}

		defer resp.Body.Close()
		body, err := ioutil.ReadAll(resp.Body)
		if err != nil {
			return nil, err
		}

		return body, nil
	})
	if err != nil {
		return nil, err
	}

	return body.([]byte), nil
}

See example for details.

License

The MIT License (MIT)

See LICENSE for details.