vmselect: allow proxying requests to vmalert (#2833)

The change allows to proxy requests with prefix `/vmalert`
to the vmalert component if `-vmalert.proxyURL` is set.

See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2825
and https://github.com/VictoriaMetrics/VictoriaMetrics/pull/2831

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

README.md

@@ -252,6 +252,9 @@ See [trobuleshooting docs](https://docs.victoriametrics.com/Troubleshooting.html
   Note that the `delete_series` handler should be used only in exceptional cases such as deletion of accidentally ingested incorrect time series. It shouldn't
   be used on a regular basis, since it carries non-zero overhead.
 
+- URL for accessing [vmalert's](https://docs.victoriametrics.com/vmalert.html) UI: `http://<vmselect>:8481/select/<accountID>/prometheus/vmalert/home`.
+  This URL works only when `-vmalert.proxyURL` flag is set. See more about vmalert [here](#vmalert). 
+
 - `vmstorage` nodes provide the following HTTP endpoints on `8482` port:
   - `/internal/force_merge` - initiate [forced compactions](https://docs.victoriametrics.com/#forced-merge) on the given `vmstorage` node.
   - `/snapshot/create` - create [instant snapshot](https://medium.com/@valyala/how-victoriametrics-makes-instant-snapshots-for-multi-terabyte-time-series-data-e1f3fb0e0282),
@@ -464,6 +467,17 @@ curl http://0.0.0.0:8480/debug/pprof/heap > mem.pprof
 
 </div>
 
+## vmalert
+
+vmselect is capable of proxying requests to [vmalert](https://docs.victoriametrics.com/vmalert.html)
+when `-vmalert.proxyURL` flag is set. Use this feature for the following cases:
+* for proxying requests from [Grafana Alerting UI](https://grafana.com/docs/grafana/latest/alerting/);
+* for accessing vmalert's UI through vmselect's Web interface.
+
+For accessing vmalert's UI through vmselect configure `-vmalert.proxyURL` flag and visit
+`http://<vmselect>:8481/select/<accountID>/prometheus/vmalert/home` link.
+
+
 ## Community and contributions
 
 We are open to third-party pull requests provided they follow the [KISS design principle](https://en.wikipedia.org/wiki/KISS_principle):
@@ -817,7 +831,7 @@ Below is the output for `/path/to/vmselect -help`:
   -version
      Show VictoriaMetrics version
   -vmalert.proxyURL string
-     Optional URL for proxying alerting API requests from Grafana. For example, if -vmalert.proxyURL is set to http://vmalert:8880 , then requests to /api/v1/rules are proxied to http://vmalert:8880/api/v1/rules
+     Optional URL for proxying requests to vmalert. For example, if -vmalert.proxyURL=http://vmalert:8880 , then alerting API requests such as /api/v1/rules from Grafana will be proxied to http://vmalert:8880/api/v1/rules
   -vmstorageDialTimeout duration
      Timeout for establishing RPC connections from vmselect to vmstorage (default 5s)
 ```

app/vmselect/main.go

@@ -44,7 +44,7 @@ var (
 		"equal to -dedup.minScrapeInterval > 0. See https://docs.victoriametrics.com/#deduplication for details")
 	resetCacheAuthKey    = flag.String("search.resetCacheAuthKey", "", "Optional authKey for resetting rollup cache via /internal/resetRollupResultCache call")
 	logSlowQueryDuration = flag.Duration("search.logSlowQueryDuration", 5*time.Second, "Log queries with execution time exceeding this value. Zero disables slow query logging")
-	vmalertProxyURL      = flag.String("vmalert.proxyURL", "", "Optional URL for proxying alerting API requests from Grafana. For example, if -vmalert.proxyURL is set to http://vmalert:8880 , then requests to /api/v1/rules are proxied to http://vmalert:8880/api/v1/rules")
+	vmalertProxyURL      = flag.String("vmalert.proxyURL", "", "Optional URL for proxying requests to vmalert. For example, if -vmalert.proxyURL=http://vmalert:8880 , then alerting API requests such as /api/v1/rules from Grafana will be proxied to http://vmalert:8880/api/v1/rules")
 	storageNodes         = flagutil.NewArray("storageNode", "Comma-separated addresses of vmstorage nodes; usage: -storageNode=vmstorage-host1,...,vmstorage-hostN")
 )
 
@@ -320,6 +320,18 @@ func selectHandler(qt *querytracer.Tracer, startTime time.Time, w http.ResponseW
 		return true
 	}
 
+	if strings.HasPrefix(p.Suffix, "prometheus/vmalert") {
+		vmalertRequests.Inc()
+		if len(*vmalertProxyURL) == 0 {
+			w.WriteHeader(http.StatusBadRequest)
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprintf(w, "%s", `{"status":"error","msg":"for accessing vmalert flag "-vmalert.proxyURL" must be configured"}`)
+			return true
+		}
+		proxyVMAlertRequests(w, r, p.Suffix)
+		return true
+	}
+
 	switch p.Suffix {
 	case "prometheus/api/v1/query":
 		queryRequests.Inc()
@@ -506,14 +518,24 @@ func selectHandler(qt *querytracer.Tracer, startTime time.Time, w http.ResponseW
 		}
 		return true
 	case "prometheus/api/v1/rules", "prometheus/rules":
-		// Return dumb placeholder for https://prometheus.io/docs/prometheus/latest/querying/api/#rules
 		rulesRequests.Inc()
-		mayProxyVMAlertRequests(w, r, p.Suffix, `{"status":"success","data":{"groups":[]}}`)
+		if len(*vmalertProxyURL) > 0 {
+			proxyVMAlertRequests(w, r, p.Suffix)
+			return true
+		}
+		// Return dumb placeholder for https://prometheus.io/docs/prometheus/latest/querying/api/#rules
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprint(w, `{"status":"success","data":{"groups":[]}}`)
 		return true
 	case "prometheus/api/v1/alerts", "prometheus/alerts":
-		// Return dumb placeholder for https://prometheus.io/docs/prometheus/latest/querying/api/#alerts
 		alertsRequests.Inc()
-		mayProxyVMAlertRequests(w, r, p.Suffix, `{"status":"success","data":{"alerts":[]}}`)
+		if len(*vmalertProxyURL) > 0 {
+			proxyVMAlertRequests(w, r, p.Suffix)
+			return true
+		}
+		// Return dumb placeholder for https://prometheus.io/docs/prometheus/latest/querying/api/#alerts
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprint(w, `{"status":"success","data":{"alerts":[]}}`)
 		return true
 	case "prometheus/api/v1/metadata":
 		// Return dumb placeholder for https://prometheus.io/docs/prometheus/latest/querying/api/#querying-metric-metadata
@@ -660,8 +682,10 @@ var (
 
 	graphiteFunctionsRequests = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/graphite/functions"}`)
 
-	rulesRequests          = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/api/v1/rules"}`)
+	vmalertRequests = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/vmalert"}`)
-	alertsRequests         = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/api/v1/alerts"}`)
+	rulesRequests   = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/api/v1/rules"}`)
+	alertsRequests  = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/api/v1/alerts"}`)
+
 	metadataRequests       = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/api/v1/metadata"}`)
 	buildInfoRequests      = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/api/v1/buildinfo"}`)
 	queryExemplarsRequests = metrics.NewCounter(`vm_http_requests_total{path="/select/{}/prometheus/api/v1/query_exemplars"}`)
@@ -679,13 +703,7 @@ See the docs at https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html .
 	flagutil.Usage(s)
 }
 
-func mayProxyVMAlertRequests(w http.ResponseWriter, r *http.Request, path, stubResponse string) {
+func proxyVMAlertRequests(w http.ResponseWriter, r *http.Request, path string) {
-	if len(*vmalertProxyURL) == 0 {
-		// Return dumb placeholder for https://prometheus.io/docs/prometheus/latest/querying/api/#rules
-		w.Header().Set("Content-Type", "application/json")
-		fmt.Fprintf(w, "%s", stubResponse)
-		return
-	}
 	defer func() {
 		err := recover()
 		if err == nil || err == http.ErrAbortHandler {

docs/CHANGELOG.md

@@ -18,6 +18,7 @@ The following tip changes can be tested by building VictoriaMetrics components f
 **Update notes:** this release introduces backwards-incompatible changes to `vm_partial_results_total` metric by changing its labels to be consistent with `vm_requests_total` metric.
 If you use alerting rules or Grafana dashboards, which rely on this metric, then they must be updated. The official dashboards for VictoriaMetrics don't use this metric.
 
+* FEATURE: [vmselect](https://docs.victoriametrics.com/#vmselect): allow accessing [vmalert's](https://docs.victoriametrics.com/vmalert.html) UI when `-vmalert.proxyURL` command-line flag is set. See more [here](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#vmalert)
 * FEATURE: add `-search.setLookbackToStep` command-line flag, which enables InfluxDB-like gap filling during querying. See [these docs](https://docs.victoriametrics.com/guides/migrate-from-influx.html) for details.
 * FEATURE: [vmui](https://docs.victoriametrics.com/#vmui): add an UI for [query tracing](https://docs.victoriametrics.com/#query-tracing). It can be enabled by clicking `enable query tracing` checkbox and re-running the query. See [this feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2703).
 * FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): add `-remoteWrite.headers` command-line option for specifying optional HTTP headers to send to the configured `-remoteWrite.url`. For example, `-remoteWrite.headers='Foo:Bar^^Baz:x'` would send `Foo: Bar` and `Baz: x` HTTP headers with every request to `-remoteWrite.url`. See [this feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2805).

docs/Cluster-VictoriaMetrics.md

@@ -256,6 +256,9 @@ See [trobuleshooting docs](https://docs.victoriametrics.com/Troubleshooting.html
   Note that the `delete_series` handler should be used only in exceptional cases such as deletion of accidentally ingested incorrect time series. It shouldn't
   be used on a regular basis, since it carries non-zero overhead.
 
+- URL for accessing [vmalert's](https://docs.victoriametrics.com/vmalert.html) UI: `http://<vmselect>:8481/select/<accountID>/prometheus/vmalert/home`.
+  This URL works only when `-vmalert.proxyURL` flag is set. See more about vmalert [here](#vmalert). 
+
 - `vmstorage` nodes provide the following HTTP endpoints on `8482` port:
   - `/internal/force_merge` - initiate [forced compactions](https://docs.victoriametrics.com/#forced-merge) on the given `vmstorage` node.
   - `/snapshot/create` - create [instant snapshot](https://medium.com/@valyala/how-victoriametrics-makes-instant-snapshots-for-multi-terabyte-time-series-data-e1f3fb0e0282),
@@ -468,6 +471,17 @@ curl http://0.0.0.0:8480/debug/pprof/heap > mem.pprof
 
 </div>
 
+## vmalert
+
+vmselect is capable of proxying requests to [vmalert](https://docs.victoriametrics.com/vmalert.html)
+when `-vmalert.proxyURL` flag is set. Use this feature for the following cases:
+* for proxying requests from [Grafana Alerting UI](https://grafana.com/docs/grafana/latest/alerting/);
+* for accessing vmalert's UI through vmselect's Web interface.
+
+For accessing vmalert's UI through vmselect configure `-vmalert.proxyURL` flag and visit
+`http://<vmselect>:8481/select/<accountID>/prometheus/vmalert/home` link.
+
+
 ## Community and contributions
 
 We are open to third-party pull requests provided they follow the [KISS design principle](https://en.wikipedia.org/wiki/KISS_principle):
@@ -821,7 +835,7 @@ Below is the output for `/path/to/vmselect -help`:
   -version
      Show VictoriaMetrics version
   -vmalert.proxyURL string
-     Optional URL for proxying alerting API requests from Grafana. For example, if -vmalert.proxyURL is set to http://vmalert:8880 , then requests to /api/v1/rules are proxied to http://vmalert:8880/api/v1/rules
+     Optional URL for proxying requests to vmalert. For example, if -vmalert.proxyURL=http://vmalert:8880 , then alerting API requests such as /api/v1/rules from Grafana will be proxied to http://vmalert:8880/api/v1/rules
   -vmstorageDialTimeout duration
      Timeout for establishing RPC connections from vmselect to vmstorage (default 5s)
 ```