app/vmalert: remove unnecessary omitempty tag for interval param (#1649)

`omitempty` tag resulted into skipping this param on marshaling,
which was used as a checksum for groups configuration. Since on
config reload checksums are compared before applying changes,
any change to `interval` only didn't trigger config reload.

https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1641
Signed-off-by: hagen1778 <roman@victoriametrics.com>

app/vmalert/config/config.go

@@ -24,7 +24,7 @@ type Group struct {
 	Type        datasource.Type `yaml:"type,omitempty"`
 	File        string
 	Name        string             `yaml:"name"`
-	Interval    utils.PromDuration `yaml:"interval,omitempty"`
+	Interval    utils.PromDuration `yaml:"interval"`
 	Rules       []Rule             `yaml:"rules"`
 	Concurrency int                `yaml:"concurrency"`
 	// ExtraFilterLabels is a list label filters applied to every rule

app/vmalert/config/config_test.go

@@ -436,7 +436,7 @@ rules:
 `)
 	})
 
-	t.Run("Ok, `for` must change cs", func(t *testing.T) {
+	t.Run("`for` change", func(t *testing.T) {
 		f(t, `
 name: TestGroup
 rules:
@@ -450,5 +450,34 @@ rules:
     expr: sum by(job) (up == 1)
 `)
 	})
-
+	t.Run("`interval` change", func(t *testing.T) {
+		f(t, `
+name: TestGroup
+interval: 2s
+rules:
+  - alert: ExampleAlertWithFor
+    expr: sum by(job) (up == 1)
+`, `
+name: TestGroup
+interval: 4s
+rules:
+  - alert: ExampleAlertWithFor
+    expr: sum by(job) (up == 1)
+`)
+	})
+	t.Run("`concurrency` change", func(t *testing.T) {
+		f(t, `
+name: TestGroup
+concurrency: 2
+rules:
+  - alert: ExampleAlertWithFor
+    expr: sum by(job) (up == 1)
+`, `
+name: TestGroup
+concurrency: 16
+rules:
+  - alert: ExampleAlertWithFor
+    expr: sum by(job) (up == 1)
+`)
+	})
 }

app/vmalert/group.go

@@ -190,6 +190,9 @@ func (g *Group) updateWith(newGroup *Group) error {
 	for _, nr := range rulesRegistry {
 		newRules = append(newRules, nr)
 	}
+	// note that g.Interval is not updated here
+	// so the value can be compared later in
+	// group.Start function
 	g.Type = newGroup.Type
 	g.Concurrency = newGroup.Concurrency
 	g.ExtraFilterLabels = newGroup.ExtraFilterLabels