vmalert: retry all errors except 4XX status codes (#4461)

vmalert: retry all errors except 4XX status codes

Retry all errors except 4XX status codes while pushing via remote-write
to the remote storage. Previously, errors like broken connection could
prevent vmalert from retrying the request.

Signed-off-by: hagen1778 <roman@victoriametrics.com>

app/vmalert/remotewrite/remotewrite.go

@@ -185,6 +185,11 @@ var (
 	bufferFlushDuration = metrics.NewHistogram(`vmalert_remotewrite_flush_duration_seconds`)
 )
 
+var (
+	retryCount   = 5
+	retryBackoff = time.Second
+)
+
 // flush is a blocking function that marshals WriteRequest and sends
 // it to remote-write endpoint. Flush performs limited amount of retries
 // if request fails.
@@ -202,12 +207,6 @@ func (c *Client) flush(ctx context.Context, wr *prompbmarshal.WriteRequest) {
 	}
 
 	b := snappy.Encode(nil, data)
-
-	const (
-		retryCount   = 5
-		retryBackoff = time.Second
-	)
-
 	for attempts := 0; attempts < retryCount; attempts++ {
 		err := c.send(ctx, b)
 		if err == nil {
@@ -216,10 +215,10 @@ func (c *Client) flush(ctx context.Context, wr *prompbmarshal.WriteRequest) {
 			return
 		}
 
-		_, isRetriable := err.(*retriableError)
-		logger.Warnf("attempt %d to send request failed: %s (retriable: %v)", attempts+1, err, isRetriable)
+		_, isNotRetriable := err.(*nonRetriableError)
+		logger.Warnf("attempt %d to send request failed: %s (retriable: %v)", attempts+1, err, !isNotRetriable)
 
-		if !isRetriable {
+		if isNotRetriable {
 			// exit fast if error isn't retriable
 			break
 		}
@@ -276,22 +275,23 @@ func (c *Client) send(ctx context.Context, data []byte) error {
 	case 2:
 		// respond with a HTTP 2xx status code when the write is successful.
 		return nil
-	case 5:
-		// respond with HTTP status code 5xx when the write fails and SHOULD be retried.
-		return &retriableError{fmt.Errorf("unexpected response code %d for %s. Response body %q",
+	case 4:
+		if resp.StatusCode != http.StatusTooManyRequests {
+			// MUST NOT retry write requests on HTTP 4xx responses other than 429
+			return &nonRetriableError{fmt.Errorf("unexpected response code %d for %s. Response body %q",
 				resp.StatusCode, req.URL.Redacted(), body)}
+		}
+		fallthrough
 	default:
-		// respond with HTTP status code 4xx when the request is invalid, will never be able to succeed
-		// and should not be retried.
 		return fmt.Errorf("unexpected response code %d for %s. Response body %q",
 			resp.StatusCode, req.URL.Redacted(), body)
 	}
 }
 
-type retriableError struct {
+type nonRetriableError struct {
 	err error
 }
 
-func (e *retriableError) Error() string {
+func (e *nonRetriableError) Error() string {
 	return e.err.Error()
 }

app/vmalert/remotewrite/remotewrite_test.go

@@ -7,6 +7,7 @@ import (
 	"math/rand"
 	"net/http"
 	"net/http/httptest"
+	"sync"
 	"sync/atomic"
 	"testing"
 	"time"
@@ -18,15 +19,30 @@ import (
 )
 
 func TestClient_Push(t *testing.T) {
+	oldRetryBackoff := retryBackoff
+	retryBackoff = time.Millisecond * 10
+	defer func() {
+		retryBackoff = oldRetryBackoff
+	}()
+
 	testSrv := newRWServer()
-	cfg := Config{
+	client, err := NewClient(context.Background(), Config{
 		Addr:         testSrv.URL,
 		MaxBatchSize: 100,
-	}
-	client, err := NewClient(context.Background(), cfg)
+	})
 	if err != nil {
 		t.Fatalf("failed to create client: %s", err)
 	}
+
+	faultySrv := newFaultyRWServer()
+	faultyClient, err := NewClient(context.Background(), Config{
+		Addr:         faultySrv.URL,
+		MaxBatchSize: 50,
+	})
+	if err != nil {
+		t.Fatalf("failed to create faulty client: %s", err)
+	}
+
 	r := rand.New(rand.NewSource(1))
 	const rowsN = 1e4
 	var sent int
@@ -38,9 +54,16 @@ func TestClient_Push(t *testing.T) {
 			}},
 		}
 		err := client.Push(s)
+		if err != nil {
+			t.Fatalf("unexpected err: %s", err)
+		}
 		if err == nil {
 			sent++
 		}
+		err = faultyClient.Push(s)
+		if err != nil {
+			t.Fatalf("unexpected err: %s", err)
+		}
 	}
 	if sent == 0 {
 		t.Fatalf("0 series sent")
@@ -48,10 +71,17 @@ func TestClient_Push(t *testing.T) {
 	if err := client.Close(); err != nil {
 		t.Fatalf("failed to close client: %s", err)
 	}
+	if err := faultyClient.Close(); err != nil {
+		t.Fatalf("failed to close faulty client: %s", err)
+	}
 	got := testSrv.accepted()
 	if got != sent {
 		t.Fatalf("expected to have %d series; got %d", sent, got)
 	}
+	got = faultySrv.accepted()
+	if got != sent {
+		t.Fatalf("expected to have %d series for faulty client; got %d", sent, got)
+	}
 }
 
 func newRWServer() *rwServer {
@@ -117,3 +147,42 @@ func (rw *rwServer) handler(w http.ResponseWriter, r *http.Request) {
 	atomic.AddUint64(&rw.acceptedRows, uint64(len(wr.Timeseries)))
 	w.WriteHeader(http.StatusNoContent)
 }
+
+// faultyRWServer sometimes respond with 5XX status code
+// or just closes the connection. Is used for testing retries.
+type faultyRWServer struct {
+	*rwServer
+
+	reqsMu sync.Mutex
+	reqs   int
+}
+
+func newFaultyRWServer() *faultyRWServer {
+	rw := &faultyRWServer{
+		rwServer: &rwServer{},
+	}
+	rw.Server = httptest.NewServer(http.HandlerFunc(rw.handler))
+	return rw
+}
+
+func (frw *faultyRWServer) handler(w http.ResponseWriter, r *http.Request) {
+	frw.reqsMu.Lock()
+	reqs := frw.reqs
+	frw.reqs++
+	if frw.reqs > 5 {
+		frw.reqs = 0
+	}
+	frw.reqsMu.Unlock()
+
+	switch reqs {
+	case 0, 1, 2, 3:
+		frw.rwServer.handler(w, r)
+	case 4:
+		hj, _ := w.(http.Hijacker)
+		conn, _, _ := hj.Hijack()
+		conn.Close()
+	case 5:
+		w.WriteHeader(http.StatusInternalServerError)
+		w.Write([]byte("server overloaded"))
+	}
+}

docs/CHANGELOG.md

@@ -43,6 +43,7 @@ The following tip changes can be tested by building VictoriaMetrics components f
 * BUGFIX: [vmbackupmanager](https://docs.victoriametrics.com/vmbackupmanager.html): fix an issue with `vmbackupmanager` not being able to restore data from a backup stored in GCS. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4420) for details.
 * BUGFIX: [storage](https://docs.victoriametrics.com/Single-server-VictoriaMetrics.html): Properly creates `parts.json` after migration from versions below `v1.90.0. It must fix errors on start-up after unclean shutdown. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4336) for details.
 * BUGFIX: [vmui](https://docs.victoriametrics.com/#vmui): fix a memory leak issue associated with chart updates. See [this pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/4455).
+* BUGFIX: [vmalert](https://docs.victoriametrics.com/vmalert.html): retry all errors except 4XX status codes while pushing via remote-write to the remote storage. Previously, errors like broken connection could prevent vmalert from retrying the request.
 
 ## [v1.91.2](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.91.2)