Vmalert extra params (#1587)

* vmalert: allow extra GET params in datasource package

ExtraParams will be added as GET params to every HTTP request made by datasource.
The `roundDigits` param, for example, was substituted by corresponding extra param.

* vmalert: add nocache=1 param for replay process

The `nocache=1` param is VictoriaMetrics specific parameter which prevents it
from caching and boundaries aligning for queries. We set it to avoid cache
pollution in `replay` mode and also to avoid unnecessary time range boundaries
alignment.

* vmalert: mention nocache=1 in replay description

* vmalert: fix bug with unused param

app/vmalert/README.md

@@ -311,6 +311,8 @@ to [/query_range](https://prometheus.io/docs/prometheus/latest/querying/api/#ran
 of the configured `-datasource.url`. Returned data then processed according to the rule type and
 backfilled to `-remoteWrite.url` via [Remote Write protocol](https://prometheus.io/docs/prometheus/latest/storage/#remote-storage-integrations).
 Vmalert respects `evaluationInterval` value set by flag or per-group during the replay.
+Vmalert automatically disables caching on VictoriaMetrics side by sending `nocache=1` param. It allows
+to prevent cache pollution and unwanted time range boundaries adjustment during backfilling.
 
 #### Recording rules
 

app/vmalert/datasource/init.go

@@ -31,8 +31,15 @@ var (
 		`In VM "round_digits" limits the number of digits after the decimal point in response values.`)
 )
 
+// Param represents an HTTP GET param
+type Param struct {
+	Key, Value string
+}
+
 // Init creates a Querier from provided flag values.
-func Init() (QuerierBuilder, error) {
+// Provided extraParams will be added as GET params to
+// each request.
+func Init(extraParams []Param) (QuerierBuilder, error) {
 	if *addr == "" {
 		return nil, fmt.Errorf("datasource.url is empty")
 	}
@@ -43,9 +50,11 @@ func Init() (QuerierBuilder, error) {
 	}
 	tr.MaxIdleConnsPerHost = *maxIdleConnections
 
-	var rd string
 	if *roundDigits > 0 {
-		rd = fmt.Sprintf("%d", *roundDigits)
+		extraParams = append(extraParams, Param{
+			Key:   "round_digits",
+			Value: fmt.Sprintf("%d", *roundDigits),
+		})
 	}
 
 	return &VMStorage{
@@ -56,7 +65,7 @@ func Init() (QuerierBuilder, error) {
 		appendTypePrefix: *appendTypePrefix,
 		lookBack:         *lookBack,
 		queryStep:        *queryStep,
-		roundDigits:      rd,
 		dataSourceType:   NewPrometheusType(),
+		extraParams:      extraParams,
 	}, nil
 }

app/vmalert/datasource/vm.go

@@ -18,11 +18,11 @@ type VMStorage struct {
 	appendTypePrefix bool
 	lookBack         time.Duration
 	queryStep        time.Duration
-	roundDigits      string
 
 	dataSourceType     Type
 	evaluationInterval time.Duration
 	extraLabels        []string
+	extraParams        []Param
 }
 
 // Clone makes clone of VMStorage, shares http client.

app/vmalert/datasource/vm_prom_api.go

@@ -155,11 +155,11 @@ func (s *VMStorage) setPrometheusReqParams(r *http.Request, query string) {
 		// override step with user-specified value
 		q.Set("step", s.queryStep.String())
 	}
-	if s.roundDigits != "" {
-		q.Set("round_digits", s.roundDigits)
-	}
 	for _, l := range s.extraLabels {
 		q.Add("extra_label", l)
 	}
+	for _, p := range s.extraParams {
+		q.Add(p.Key, p.Value)
+	}
 	r.URL.RawQuery = q.Encode()
 }

app/vmalert/datasource/vm_test.go

@@ -385,7 +385,7 @@ func TestRequestParams(t *testing.T) {
 			"round digits",
 			false,
 			&VMStorage{
-				roundDigits: "10",
+				extraParams: []Param{{"round_digits", "10"}},
 			},
 			func(t *testing.T, r *http.Request) {
 				exp := fmt.Sprintf("query=%s&round_digits=10&time=%d", query, timestamp.Unix())
@@ -421,6 +421,20 @@ func TestRequestParams(t *testing.T) {
 				checkEqualString(t, exp, r.URL.RawQuery)
 			},
 		},
+		{
+			"extra params",
+			false,
+			&VMStorage{
+				extraParams: []Param{
+					{Key: "nocache", Value: "1"},
+					{Key: "max_lookback", Value: "1h"},
+				},
+			},
+			func(t *testing.T, r *http.Request) {
+				exp := fmt.Sprintf("max_lookback=1h&nocache=1&query=%s&time=%d", query, timestamp.Unix())
+				checkEqualString(t, exp, r.URL.RawQuery)
+			},
+		},
 	}
 
 	for _, tc := range testCases {

app/vmalert/main.go

@@ -91,7 +91,10 @@ func main() {
 		if err != nil {
 			logger.Fatalf("cannot parse configuration file: %s", err)
 		}
-		q, err := datasource.Init()
+		// prevent queries from caching and boundaries aligning
+		// when querying VictoriaMetrics datasource.
+		noCache := datasource.Param{Key: "nocache", Value: "1"}
+		q, err := datasource.Init([]datasource.Param{noCache})
 		if err != nil {
 			logger.Fatalf("failed to init datasource: %s", err)
 		}
@@ -139,7 +142,7 @@ var (
 )
 
 func newManager(ctx context.Context) (*manager, error) {
-	q, err := datasource.Init()
+	q, err := datasource.Init(nil)
 	if err != nil {
 		return nil, fmt.Errorf("failed to init datasource: %w", err)
 	}