vmalert: enable configuring explicit path (#1536)

* vmalert: allow to disable automatically added path to remote write address via disablePathAppend flag
* docs: update docs to include remoteWrite.disablePathAppend

app/vmalert/README.md

@@ -502,6 +502,8 @@ The shortlist of configuration flags is the following:
     	Optional TLS server name to use for connections to -remoteWrite.url. By default the server name from -remoteWrite.url is used
   -remoteWrite.url string
     	Optional URL to VictoriaMetrics or vminsert where to persist alerts state and recording rules results in form of timeseries. E.g. http://127.0.0.1:8428
+  -remoteWrite.disablePathAppend
+     Whether to disable automatic appending of '/api/v1/write' path to the configured -remoteWrite.url.
   -replay.maxDatapointsPerQuery int
     	Max number of data points expected in one request. The higher the value, the less requests will be made during replay. (default 1000)
   -replay.ruleRetryAttempts int

app/vmalert/remotewrite/init.go

@@ -27,6 +27,7 @@ var (
 		"By default system CA is used")
 	tlsServerName = flag.String("remoteWrite.tlsServerName", "", "Optional TLS server name to use for connections to -remoteWrite.url. "+
 		"By default the server name from -remoteWrite.url is used")
+	disablePathAppend = flag.Bool("remoteWrite.disablePathAppend", false, "Whether to disable automatic appending of '/api/v1/write' path to the configured -remoteWrite.url.")
 )
 
 // Init creates Client object from given flags.
@@ -49,6 +50,7 @@ func Init(ctx context.Context) (*Client, error) {
 		FlushInterval:     *flushInterval,
 		BasicAuthUser:     *basicAuthUsername,
 		BasicAuthPass:     *basicAuthPassword,
+		DisablePathAppend: *disablePathAppend,
 		Transport:         t,
 	})
 }

app/vmalert/remotewrite/remotewrite.go

@@ -26,6 +26,7 @@ type Client struct {
 	flushInterval     time.Duration
 	maxBatchSize      int
 	maxQueueSize      int
+	disablePathAppend bool
 
 	wg     sync.WaitGroup
 	doneCh chan struct{}
@@ -56,6 +57,8 @@ type Config struct {
 	WriteTimeout time.Duration
 	// Transport will be used by the underlying http.Client
 	Transport *http.Transport
+	// DisablePathAppend can be used to not automatically append '/api/v1/write' to the remote write url
+	DisablePathAppend bool
 }
 
 const (
@@ -102,6 +105,7 @@ func NewClient(ctx context.Context, cfg Config) (*Client, error) {
 		maxQueueSize:      cfg.MaxQueueSize,
 		doneCh:            make(chan struct{}),
 		input:             make(chan prompbmarshal.TimeSeries, cfg.MaxQueueSize),
+		disablePathAppend: cfg.DisablePathAppend,
 	}
 	cc := defaultConcurrency
 	if cfg.Concurrency > 0 {
@@ -231,7 +235,9 @@ func (c *Client) send(ctx context.Context, data []byte) error {
 	if c.baPass != "" {
 		req.SetBasicAuth(c.baUser, c.baPass)
 	}
+	if !c.disablePathAppend {
 		req.URL.Path += writePath
+	}
 	resp, err := c.c.Do(req.WithContext(ctx))
 	if err != nil {
 		return fmt.Errorf("error while sending request to %s: %w; Data len %d(%d)",

docs/vmalert.md

@@ -506,6 +506,8 @@ The shortlist of configuration flags is the following:
     	Optional TLS server name to use for connections to -remoteWrite.url. By default the server name from -remoteWrite.url is used
   -remoteWrite.url string
     	Optional URL to VictoriaMetrics or vminsert where to persist alerts state and recording rules results in form of timeseries. E.g. http://127.0.0.1:8428
+  -remoteWrite.disablePathAppend
+    	Whether to disable automatic appending of '/api/v1/write' path to the configured -remoteWrite.url.
   -replay.maxDatapointsPerQuery int
     	Max number of data points expected in one request. The higher the value, the less requests will be made during replay. (default 1000)
   -replay.ruleRetryAttempts int