prometheus/rules/alerting.go

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// Copyright 2013 Prometheus Team
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package rules
import (
"github.com/prometheus/prometheus/model"
"github.com/prometheus/prometheus/rules/ast"
"github.com/prometheus/prometheus/utility"
"time"
)
// States that active alerts can be in.
type alertState int
func (s alertState) String() (state string) {
switch s {
case PENDING:
state = "pending"
case FIRING:
state = "firing"
}
return
}
const (
PENDING alertState = iota
FIRING
)
// alert is used to track active (pending/firing) alerts over time.
type alert struct {
// The name of the alert.
name string
// The vector element labelset triggering this alert.
metric model.Metric
// The state of the alert (PENDING or FIRING).
state alertState
// The time when the alert first transitioned into PENDING state.
activeSince time.Time
}
// sample returns a Sample suitable for recording the alert.
func (a alert) sample(timestamp time.Time, value model.SampleValue) model.Sample {
recordedMetric := model.Metric{}
for label, value := range a.metric {
recordedMetric[label] = value
}
recordedMetric[model.MetricNameLabel] = model.AlertMetricName
recordedMetric[model.AlertNameLabel] = model.LabelValue(a.name)
recordedMetric[model.AlertStateLabel] = model.LabelValue(a.state.String())
return model.Sample{
Metric: recordedMetric,
Value: value,
Timestamp: timestamp,
}
}
// An alerting rule generates alerts from its vector expression.
type AlertingRule struct {
// The name of the alert.
name string
// The vector expression from which to generate alerts.
vector ast.VectorNode
// The duration for which a labelset needs to persist in the expression
// output vector before an alert transitions from PENDING to FIRING state.
holdDuration time.Duration
// Extra labels to attach to the resulting alert sample vectors.
labels model.LabelSet
// A map of alerts which are currently active (PENDING or FIRING), keyed by
// the fingerprint of the labelset they correspond to.
activeAlerts map[model.Fingerprint]*alert
}
func (rule AlertingRule) Name() string { return rule.name }
func (rule AlertingRule) EvalRaw(timestamp time.Time) (vector ast.Vector, err error) {
return ast.EvalVectorInstant(rule.vector, timestamp)
}
func (rule AlertingRule) Eval(timestamp time.Time) (vector ast.Vector, err error) {
// Get the raw value of the rule expression.
exprResult, err := rule.EvalRaw(timestamp)
if err != nil {
return
}
// Create pending alerts for any new vector elements in the alert expression.
resultFingerprints := utility.Set{}
for _, sample := range exprResult {
fp := model.NewFingerprintFromMetric(sample.Metric)
resultFingerprints.Add(fp)
if _, ok := rule.activeAlerts[fp]; !ok {
rule.activeAlerts[fp] = &alert{
name: rule.name,
metric: sample.Metric,
state: PENDING,
activeSince: timestamp,
}
}
}
// Check if any pending alerts should be removed or fire now. Write out alert timeseries.
for fp, activeAlert := range rule.activeAlerts {
if !resultFingerprints.Has(fp) {
vector = append(vector, activeAlert.sample(timestamp, 0))
delete(rule.activeAlerts, fp)
continue
}
if activeAlert.state == PENDING && timestamp.Sub(activeAlert.activeSince) >= rule.holdDuration {
vector = append(vector, activeAlert.sample(timestamp, 0))
activeAlert.state = FIRING
}
vector = append(vector, activeAlert.sample(timestamp, 1))
}
return
}
// Construct a new AlertingRule.
func NewAlertingRule(name string, vector ast.VectorNode, holdDuration time.Duration, labels model.LabelSet) *AlertingRule {
return &AlertingRule{
name: name,
vector: vector,
holdDuration: holdDuration,
labels: labels,
activeAlerts: map[model.Fingerprint]*alert{},
}
}