feat(alerta-service): Add custom severities to Alerta handler

Fix influxdata#2056

This commit allows usage of all or some Alerta Severities. It provides two keywords to fine tune kapacitor built-in severities.

1. First, you can rename kapacitor serverity levels: crit, warn, info, ok to any other severities configured in your Alerta:

    |alert()
        // ...
        .alerta()
            // ...
            .renameSeverity('crit', 'major')
            .renameSeverity('info', 'notice')

I suppose this will cover most of the cases. But if you do want a lot of severity levels:

2. You can add custom severity levels, which will be avaluated on Alerta handler level after built-in alert was triggered.

    |alert()
        // ...
        .warn(lambda: "cpu" > 50)
        .alerta()
            // ...
            .addSeverity('minor', 3, lambda: "cpu" > 60)
            .addSeverity('major', 2, lambda: "cpu" > 70)
            .addSeverity('critical', 1, lambda: "cpu" > 80)
            .addSeverity('fatal', 0, lambda: "cpu" > 90)

Note: evaluation of addSeverity condition only happen after build-in alert is triggered, so you need some entry point (like .warn() in exmple), which should cover all range of values interesting to you.
Note: this severities use Alerta's code order - higher severity has lower code (0 for fatal, 9 for ok)
Note: .addSeverity() is quite useless in combination with .stateChangesOnly(), but Alerta has decent deduplication mechanism, so it shouldn't be a problem

alert.go

@@ -366,6 +366,23 @@ func newAlertNode(et *ExecutingTask, n *pipeline.AlertNode, d NodeDiagnostic) (a
 		if a.Environment != "" {
 			c.Environment = a.Environment
 		}
+		if len(a.RenameSeverities) != 0 {
+			c.RenameSeverities = a.RenameSeverities
+		}
+		if len(a.ExtraSeverities) != 0 {
+			c.ExtraSeverityExpressions = make([]stateful.Expression, len(a.ExtraSeverities))
+			c.ExtraSeverityNames = make([]string, len(a.ExtraSeverities))
+			c.ExtraSeverityScopePools = make([]stateful.ScopePool, len(a.ExtraSeverities))
+			for i, severity := range a.ExtraSeverities {
+				statefulExpression, expressionCompileError := stateful.NewExpression(severity.Condition.Expression)
+				if expressionCompileError != nil {
+					return nil, fmt.Errorf("Failed to compile stateful expression for Alerta extra severity %s: %s", severity.Name, expressionCompileError)
+				}
+				c.ExtraSeverityExpressions[i] = statefulExpression
+				c.ExtraSeverityNames[i] = severity.Name
+				c.ExtraSeverityScopePools[i] = stateful.NewScopePool(ast.FindReferenceVariables(severity.Condition.Expression))
+			}
+		}
 		if a.Group != "" {
 			c.Group = a.Group
 		}

integrations/streamer_test.go

@@ -9197,11 +9197,17 @@ stream
 			.token('testtoken1234567')
 			.environment('production')
 			.timeout(1h)
+		.alerta()
+			.token('testtoken7654321')
+			.environment('production')
+			.timeout(1h)
+			.addSeverity('fatal', 0, lambda: "count" > 9.0)
 		.alerta()
 			.token('anothertesttoken')
 			.resource('resource: {{ index .Tags "host" }}')
 			.event('event: {{ .TaskName }}')
 			.environment('{{ index .Tags "host" }}')
+			.renameSeverity('crit', 'major')
 			.origin('override')
 			.group('{{ .ID }}')
 			.value('{{ index .Fields "count" }}')
@@ -9227,6 +9233,23 @@ stream
 				Event:       "serverA",
 				Group:       "host=serverA",
 				Environment: "production",
+				Severity:    "critical",
+				Text:        "kapacitor/cpu/serverA is CRITICAL @1971-01-01 00:00:10 +0000 UTC",
+				Origin:      "Kapacitor",
+				Service:     []string{"cpu"},
+				Correlate:   []string{"cpu"},
+				Timeout:     3600,
+			},
+		},
+		alertatest.Request{
+			URL:           "/alert",
+			Authorization: "Bearer testtoken7654321",
+			PostData: alertatest.PostData{
+				Resource:    "cpu",
+				Event:       "serverA",
+				Group:       "host=serverA",
+				Environment: "production",
+				Severity:    "fatal",
 				Text:        "kapacitor/cpu/serverA is CRITICAL @1971-01-01 00:00:10 +0000 UTC",
 				Origin:      "Kapacitor",
 				Service:     []string{"cpu"},
@@ -9242,6 +9265,7 @@ stream
 				Event:       "event: TestStream_Alert",
 				Group:       "serverA",
 				Environment: "serverA",
+				Severity:    "major",
 				Text:        "kapacitor/cpu/serverA is CRITICAL @1971-01-01 00:00:10 +0000 UTC",
 				Origin:      "override",
 				Service:     []string{"serviceA", "serviceB", "cpu"},

pipeline/alert.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"reflect"
+	"sort"
 	"strings"
 	"time"
 
@@ -1219,6 +1220,12 @@ func (n *AlertNodeData) Alerta() *AlertaHandler {
 	return alerta
 }
 
+type AlertaCustomSeverity struct {
+	Name      string          `json:"name"`
+	Code      int64           `json:"code"`
+	Condition *ast.LambdaNode `json:"condition"`
+}
+
 // tick:embedded:AlertNode.Alerta
 type AlertaHandler struct {
 	*AlertNodeData `json:"-"`
@@ -1242,6 +1249,13 @@ type AlertaHandler struct {
 	// Defaut is set from the configuration.
 	Environment string `json:"environment"`
 
+	// Alerta supports many different severity levels. And it allows you to add even more.
+	// To benefit from this model we can use two ways:
+	// Rename kapacitor built-in severities to match some of alerta's severities
+	RenameSeverities map[string]string `tick:"RenameSeverity" json:"rename-severities"`
+	// Add post-processing to kapacitor alerts to fine tune severity levels
+	ExtraSeverities []*AlertaCustomSeverity `tick:"AddSeverity" json:"add-severities"`
+
 	// Alerta group.
 	// Can be a template and has access to the same data as the AlertNode.Details property.
 	// Default: {{ .Group }}
@@ -1268,6 +1282,24 @@ type AlertaHandler struct {
 	Timeout time.Duration `json:"timeout"`
 }
 
+func (a *AlertaHandler) RenameSeverity(kapacitorName string, alertaName string) *AlertaHandler {
+	if a.RenameSeverities == nil {
+		a.RenameSeverities = make(map[string]string)
+	}
+	a.RenameSeverities[kapacitorName] = alertaName
+	return a
+}
+func (a *AlertaHandler) AddSeverity(name string, code int64, condition *ast.LambdaNode) *AlertaHandler {
+	a.ExtraSeverities = append(a.ExtraSeverities, &AlertaCustomSeverity{
+		Name:      name,
+		Code:      code,
+		Condition: condition,
+	})
+	// Alerta severities have ascending order: higher severity has lower code (1 for critical, 9 for ok)
+	sort.SliceStable(a.ExtraSeverities, func(i, j int) bool { return a.ExtraSeverities[i].Code > a.ExtraSeverities[j].Code })
+	return a
+}
+
 // List of effected services.
 // If not specified defaults to the Name of the stream.
 // tick:property

pipeline/tick/alert.go

@@ -220,8 +220,20 @@ func (n *AlertNode) Build(a *pipeline.AlertNode) (ast.Node, error) {
 			Dot("token", h.Token).
 			Dot("resource", h.Resource).
 			Dot("event", h.Event).
-			Dot("environment", h.Environment).
-			Dot("group", h.Group).
+			Dot("environment", h.Environment)
+
+		var severitiesOrder = []string{"ok", "info", "warn", "crit"}
+		for _, k := range severitiesOrder {
+			if val, ok := h.RenameSeverities[k]; ok {
+				n.Dot("renameSeverity", k, val)
+			}
+		}
+
+		for _, k := range h.ExtraSeverities {
+			n.Dot("addSeverity", k.Name, k.Code, k.Condition)
+		}
+
+		n.Dot("group", h.Group).
 			Dot("value", h.Value).
 			Dot("origin", h.Origin).
 			Dot("services", args(h.Service)...).

pipeline/tick/alert_test.go

@@ -661,6 +661,14 @@ func TestAlertAlerta(t *testing.T) {
 	handler.Resource = "Harbinger"
 	handler.Event = "Jump through Omega-4 Relay"
 	handler.Environment = "Collector base"
+	handler.RenameSeverities = make(map[string]string)
+	handler.RenameSeverities["info"] = "notice"
+	handler.ExtraSeverities = make([]*pipeline.AlertaCustomSeverity, 1)
+	handler.ExtraSeverities[0] = &pipeline.AlertaCustomSeverity{
+		Name:      "major",
+		Code:      2,
+		Condition: newLambda(85),
+	}
 	handler.Group = "I brought Jack, Miranda and Tali"
 	handler.Value = "Save the Galaxy"
 	handler.Origin = "Omega"
@@ -680,6 +688,8 @@ func TestAlertAlerta(t *testing.T) {
         .resource('Harbinger')
         .event('Jump through Omega-4 Relay')
         .environment('Collector base')
+        .renameSeverity('info', 'notice')
+        .addSeverity('major', 2, lambda: "cpu" > 85)
         .group('I brought Jack, Miranda and Tali')
         .value('Save the Galaxy')
         .origin('Omega')

server/server_test.go

@@ -10148,6 +10148,7 @@ func TestServer_AlertHandlers(t *testing.T) {
 						Event:       "id",
 						Group:       "test",
 						Environment: "env",
+						Severity:    "critical",
 						Text:        "message",
 						Origin:      "kapacitor",
 						Service:     []string{"alert"},

services/alerta/alertatest/alertatest.go

@@ -57,6 +57,7 @@ type PostData struct {
 	Event       string   `json:"event"`
 	Group       string   `json:"group"`
 	Environment string   `json:"environment"`
+	Severity    string   `json:"severity"`
 	Text        string   `json:"text"`
 	Origin      string   `json:"origin"`
 	Service     []string `json:"service"`

services/alerta/service.go

@@ -17,6 +17,8 @@ import (
 	khttp "github.com/influxdata/kapacitor/http"
 	"github.com/influxdata/kapacitor/keyvalue"
 	"github.com/influxdata/kapacitor/models"
+	"github.com/influxdata/kapacitor/tick/ast"
+	"github.com/influxdata/kapacitor/tick/stateful"
 	"github.com/pkg/errors"
 )
 
@@ -267,6 +269,16 @@ type HandlerConfig struct {
 	// Defaut is set from the configuration.
 	Environment string `mapstructure:"environment"`
 
+	// Renaming rules for severities
+	// Allows to rewrite build-in kapacitor severities (info, warn, crit) to any of Alerta multiple severities
+	RenameSeverities map[string]string `mapstructure:"rename-severities"`
+
+	// Expressions for custom Alerta severities
+	// Allows to fine tune severity levels of kapacitor
+	ExtraSeverityExpressions []stateful.Expression `mapstructure:"severity-expressions"`
+	ExtraSeverityNames       []string              `mapstructure:"severity-names"`
+	ExtraSeverityScopePools  []stateful.ScopePool  `mapstructure:"severity-scope-pool"`
+
 	// Alerta group.
 	// Can be a template and has access to the same data as the AlertNode.Details property.
 	// Default: {{ .Group }}
@@ -297,13 +309,17 @@ type handler struct {
 	c    HandlerConfig
 	diag Diagnostic
 
-	resourceTmpl    *text.Template
-	eventTmpl       *text.Template
-	environmentTmpl *text.Template
-	valueTmpl       *text.Template
-	groupTmpl       *text.Template
-	serviceTmpl     []*text.Template
-	correlateTmpl   []*text.Template
+	resourceTmpl        *text.Template
+	eventTmpl           *text.Template
+	environmentTmpl     *text.Template
+	renameSeverities    map[string]string
+	severityLevels      []string
+	severityExpressions []stateful.Expression
+	scopePools          []stateful.ScopePool
+	valueTmpl           *text.Template
+	groupTmpl           *text.Template
+	serviceTmpl         []*text.Template
+	correlateTmpl       []*text.Template
 }
 
 func (s *Service) DefaultHandlerConfig() HandlerConfig {
@@ -357,16 +373,20 @@ func (s *Service) Handler(c HandlerConfig, ctx ...keyvalue.T) (alert.Handler, er
 	}
 
 	return &handler{
-		s:               s,
-		c:               c,
-		diag:            s.diag.WithContext(ctx...),
-		resourceTmpl:    rtmpl,
-		eventTmpl:       evtmpl,
-		environmentTmpl: etmpl,
-		groupTmpl:       gtmpl,
-		valueTmpl:       vtmpl,
-		serviceTmpl:     stmpl,
-		correlateTmpl:   ctmpl,
+		s:                   s,
+		c:                   c,
+		diag:                s.diag.WithContext(ctx...),
+		resourceTmpl:        rtmpl,
+		eventTmpl:           evtmpl,
+		environmentTmpl:     etmpl,
+		renameSeverities:    c.RenameSeverities,
+		severityLevels:      c.ExtraSeverityNames,
+		severityExpressions: c.ExtraSeverityExpressions,
+		scopePools:          c.ExtraSeverityScopePools,
+		groupTmpl:           gtmpl,
+		valueTmpl:           vtmpl,
+		serviceTmpl:         stmpl,
+		correlateTmpl:       ctmpl,
 	}, nil
 }
 
@@ -468,20 +488,39 @@ func (h *handler) Handle(event alert.Event) {
 	}
 
 	var severity string
+	var severityKey string
 
 	switch event.State.Level {
 	case alert.OK:
 		severity = "ok"
+		severityKey = "ok"
 	case alert.Info:
 		severity = "informational"
+		severityKey = "info"
 	case alert.Warning:
 		severity = "warning"
+		severityKey = "warn"
 	case alert.Critical:
 		severity = "critical"
+		severityKey = "crit"
 	default:
 		severity = "indeterminate"
 	}
 
+	if val, ok := h.renameSeverities[severityKey]; ok {
+		severity = val
+	}
+
+	if len(h.severityLevels) != 0 {
+		for i, expression := range h.severityExpressions {
+			if pass, err := EvalPredicate(expression, h.scopePools[i], event.State.Time, event.Data.Fields, event.Data.Tags); err != nil {
+				h.diag.Error("error evaluating expression for Alerta severity", err)
+			} else if pass {
+				severity = h.severityLevels[i]
+			}
+		}
+	}
+
 	if err := h.s.Alert(
 		h.c.Token,
 		h.c.TokenPrefix,
@@ -502,3 +541,54 @@ func (h *handler) Handle(event alert.Event) {
 		h.diag.Error("failed to send event to Alerta", err)
 	}
 }
+
+func EvalPredicate(se stateful.Expression, scopePool stateful.ScopePool, now time.Time, fields models.Fields, tags models.Tags) (bool, error) {
+	vars := scopePool.Get()
+	defer scopePool.Put(vars)
+	err := fillScope(vars, scopePool.ReferenceVariables(), now, fields, tags)
+	if err != nil {
+		return false, err
+	}
+
+	// for function signature check
+	if _, err := se.Type(vars); err != nil {
+		return false, err
+	}
+
+	return se.EvalBool(vars)
+}
+
+// fillScope - given a scope and reference variables, we fill the exact variables from the now, fields and tags.
+func fillScope(vars *stateful.Scope, referenceVariables []string, now time.Time, fields models.Fields, tags models.Tags) error {
+	for _, refVariableName := range referenceVariables {
+		if refVariableName == "time" {
+			vars.Set("time", now.Local())
+			continue
+		}
+
+		// Support the error with tags/fields collision
+		var fieldValue interface{}
+		var isFieldExists bool
+		var tagValue interface{}
+		var isTagExists bool
+
+		if fieldValue, isFieldExists = fields[refVariableName]; isFieldExists {
+			vars.Set(refVariableName, fieldValue)
+		}
+
+		if tagValue, isTagExists = tags[refVariableName]; isTagExists {
+			if isFieldExists {
+				return fmt.Errorf("cannot have field and tags with same name %q", refVariableName)
+			}
+			vars.Set(refVariableName, tagValue)
+		}
+		if !isFieldExists && !isTagExists {
+			if !vars.Has(refVariableName) {
+				vars.Set(refVariableName, ast.MissingValue)
+			}
+
+		}
+	}
+
+	return nil
+}