feat: support configuring a minimum number of requests

cbreaker/cbreaker.go

@@ -8,6 +8,8 @@
 //
 // Once the Circuit breaker condition is met, it enters the "Tripped" state, where it activates fallback scenario
 // for all requests during the FallbackDuration time period and reset the stats for the location.
+// RequestVolumeThreshold can be used to require a minimum number of requests in the rolling window
+// before the condition is evaluated.
 //
 // After FallbackDuration time period passes, Circuit breaker enters "Recovering" state, during that state it will
 // start passing some traffic back to the endpoints, increasing the amount of passed requests using linear function:
@@ -56,6 +58,8 @@ type CircuitBreaker struct {
 	checkPeriod time.Duration
 	lastCheck   clock.Time
 
+	requestVolumeThreshold int64
+
 	fallback http.Handler
 	next     http.Handler
 
@@ -251,6 +255,10 @@ func (c *CircuitBreaker) checkAndSet() {
 		return
 	}
 
+	if c.metrics.TotalCount() < c.requestVolumeThreshold {
+		return
+	}
+
 	if !c.condition(c) {
 		return
 	}

cbreaker/cbreaker_test.go

@@ -207,6 +207,42 @@ func TestCircuitBreaker_triggerDuringRecovery(t *testing.T) {
 	assert.Equal(t, cbState(stateTripped), cb.state)
 }
 
+func TestCircuitBreaker_requestVolumeThreshold(t *testing.T) {
+	handler := http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusGatewayTimeout)
+	})
+
+	testutils.FreezeTime(t)
+
+	cb, err := New(handler, triggerNetRatio, RequestVolumeThreshold(20))
+	require.NoError(t, err)
+
+	srv := httptest.NewServer(cb)
+	t.Cleanup(srv.Close)
+
+	cb.metrics = statsResponseCodes(statusCode{Code: http.StatusGatewayTimeout, Count: 18})
+
+	clock.Advance(defaultCheckPeriod + clock.Millisecond)
+
+	re, _, err := testutils.Get(srv.URL)
+	require.NoError(t, err)
+	assert.Equal(t, http.StatusGatewayTimeout, re.StatusCode)
+	assert.Equal(t, cbState(stateStandby), cb.state)
+
+	cb.metrics = statsResponseCodes(statusCode{Code: http.StatusGatewayTimeout, Count: 19})
+
+	clock.Advance(defaultCheckPeriod + clock.Millisecond)
+
+	re, _, err = testutils.Get(srv.URL)
+	require.NoError(t, err)
+	assert.Equal(t, http.StatusGatewayTimeout, re.StatusCode)
+	assert.Equal(t, cbState(stateTripped), cb.state)
+
+	re, _, err = testutils.Get(srv.URL)
+	require.NoError(t, err)
+	assert.Equal(t, http.StatusServiceUnavailable, re.StatusCode)
+}
+
 func TestCircuitBreaker_sideEffects(t *testing.T) {
 	srv1Chan := make(chan *http.Request, 1)
 

cbreaker/options.go

@@ -53,6 +53,15 @@ func CheckPeriod(d time.Duration) Option {
 	}
 }
 
+// RequestVolumeThreshold sets the minimum number of requests in the rolling
+// window before the CircuitBreaker can trip. Defaults to 0.
+func RequestVolumeThreshold(n int64) Option {
+	return func(c *CircuitBreaker) error {
+		c.requestVolumeThreshold = n
+		return nil
+	}
+}
+
 // OnTripped sets a SideEffect to run when entering the Tripped state.
 // Only one SideEffect can be set for this hook.
 func OnTripped(s SideEffect) Option {