prometheus/rules/alerting.go

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// Copyright 2013 The Prometheus Authors
// 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 (
"fmt"
"html/template"
"sync"
"time"
"github.com/prometheus/common/model"
"github.com/prometheus/prometheus/promql"
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"github.com/prometheus/prometheus/util/strutil"
)
const (
// AlertMetricName is the metric name for synthetic alert timeseries.
alertMetricName model.LabelValue = "ALERTS"
// AlertNameLabel is the label name indicating the name of an alert.
alertNameLabel model.LabelName = "alertname"
// AlertStateLabel is the label name indicating the state of an alert.
alertStateLabel model.LabelName = "alertstate"
)
// AlertState denotes the state of an active alert.
type AlertState int
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const (
// StateInactive is the state of an alert that is neither firing nor pending.
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StateInactive AlertState = iota
// StatePending is the state of an alert that has been active for less than
// the configured threshold duration.
StatePending
// StateFiring is the state of an alert that has been active for longer than
// the configured threshold duration.
StateFiring
)
func (s AlertState) String() string {
switch s {
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case StateInactive:
return "inactive"
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case StatePending:
return "pending"
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case StateFiring:
return "firing"
}
panic(fmt.Errorf("unknown alert state: %v", s.String()))
}
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// Alert is the user-level representation of a single instance of an alerting rule.
type Alert struct {
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State AlertState
Labels model.LabelSet
// The value at the last evaluation of the alerting expression.
Value model.SampleValue
// The interval during which the condition of this alert held true.
// ResolvedAt will be 0 to indicate a still active alert.
ActiveAt, ResolvedAt model.Time
}
// An AlertingRule generates alerts from its vector expression.
type AlertingRule struct {
// The name of the alert.
name string
// The vector expression from which to generate alerts.
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vector promql.Expr
// 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
// Non-identifying key/value pairs.
annotations model.LabelSet
// Protects the below.
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mtx sync.Mutex
// A map of alerts which are currently active (Pending or Firing), keyed by
// the fingerprint of the labelset they correspond to.
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active map[model.Fingerprint]*Alert
}
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// NewAlertingRule constructs a new AlertingRule.
func NewAlertingRule(name string, vec promql.Expr, hold time.Duration, lbls, anns model.LabelSet) *AlertingRule {
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return &AlertingRule{
name: name,
vector: vec,
holdDuration: hold,
labels: lbls,
annotations: anns,
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active: map[model.Fingerprint]*Alert{},
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}
}
// Name returns the name of the alert.
func (rule *AlertingRule) Name() string {
return rule.name
}
func (r *AlertingRule) equal(o *AlertingRule) bool {
return r.name == o.name && r.labels.Equal(o.labels)
}
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func (r *AlertingRule) sample(alert *Alert, ts model.Time, set bool) *model.Sample {
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metric := model.Metric(r.labels.Clone())
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for ln, lv := range alert.Labels {
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metric[ln] = lv
}
metric[model.MetricNameLabel] = alertMetricName
metric[model.AlertNameLabel] = model.LabelValue(r.name)
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metric[alertStateLabel] = model.LabelValue(alert.State.String())
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s := &model.Sample{
Metric: metric,
Timestamp: ts,
Value: 0,
}
if set {
s.Value = 1
}
return s
}
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// resolvedRetention is the duration for which a resolved alert instance
// is kept in memory state and consequentally repeatedly sent to the AlertManager.
const resolvedRetention = 15 * time.Minute
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// eval evaluates the rule expression and then creates pending alerts and fires
// or removes previously pending alerts accordingly.
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func (r *AlertingRule) eval(ts model.Time, engine *promql.Engine) (model.Vector, error) {
query, err := engine.NewInstantQuery(r.vector.String(), ts)
if err != nil {
return nil, err
}
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res, err := query.Exec().Vector()
if err != nil {
return nil, err
}
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r.mtx.Lock()
defer r.mtx.Unlock()
// Create pending alerts for any new vector elements in the alert expression
// or update the expression value for existing elements.
resultFPs := map[model.Fingerprint]struct{}{}
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for _, smpl := range res {
fp := smpl.Metric.Fingerprint()
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resultFPs[fp] = struct{}{}
if alert, ok := r.active[fp]; ok && alert.State != StateInactive {
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alert.Value = smpl.Value
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continue
}
delete(smpl.Metric, model.MetricNameLabel)
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r.active[fp] = &Alert{
Labels: model.LabelSet(smpl.Metric),
ActiveAt: ts,
State: StatePending,
Value: smpl.Value,
}
}
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var vec model.Vector
// Check if any pending alerts should be removed or fire now. Write out alert timeseries.
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for fp, a := range r.active {
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if _, ok := resultFPs[fp]; !ok {
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if a.State != StateInactive {
vec = append(vec, r.sample(a, ts, false))
}
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// If the alert was previously firing, keep it around for a given
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// retention time so it is reported as resolved to the AlertManager.
if a.State == StatePending || (a.ResolvedAt != 0 && ts.Sub(a.ResolvedAt) > resolvedRetention) {
delete(r.active, fp)
}
if a.State != StateInactive {
a.State = StateInactive
a.ResolvedAt = ts
}
continue
}
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if a.State == StatePending && ts.Sub(a.ActiveAt) >= r.holdDuration {
vec = append(vec, r.sample(a, ts, false))
a.State = StateFiring
}
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vec = append(vec, r.sample(a, ts, true))
}
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return vec, nil
}
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// State returns the maximum state of alert instances for this rule.
// StateFiring > StatePending > StateInactive
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func (r *AlertingRule) State() AlertState {
r.mtx.Lock()
defer r.mtx.Unlock()
maxState := StateInactive
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for _, a := range r.active {
if a.State > maxState {
maxState = a.State
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}
}
return maxState
}
// ActiveAlerts returns a slice of active alerts.
func (r *AlertingRule) ActiveAlerts() []*Alert {
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var res []*Alert
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for _, a := range r.currentAlerts() {
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if a.ResolvedAt == 0 {
res = append(res, a)
}
}
return res
}
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// currentAlerts returns all instances of alerts for this rule. This may include
// inactive alerts that were previously firing.
func (r *AlertingRule) currentAlerts() []*Alert {
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r.mtx.Lock()
defer r.mtx.Unlock()
alerts := make([]*Alert, 0, len(r.active))
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for _, a := range r.active {
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labels := r.labels.Clone()
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for ln, lv := range a.Labels {
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labels[ln] = lv
}
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anew := *a
anew.Labels = labels
alerts = append(alerts, &anew)
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}
return alerts
}
func (rule *AlertingRule) String() string {
s := fmt.Sprintf("ALERT %s", rule.name)
s += fmt.Sprintf("\n\tIF %s", rule.vector)
if rule.holdDuration > 0 {
s += fmt.Sprintf("\n\tFOR %s", model.Duration(rule.holdDuration))
}
if len(rule.labels) > 0 {
s += fmt.Sprintf("\n\tLABELS %s", rule.labels)
}
if len(rule.annotations) > 0 {
s += fmt.Sprintf("\n\tANNOTATIONS %s", rule.annotations)
}
return s
}
// HTMLSnippet returns an HTML snippet representing this alerting rule. The
// resulting snippet is expected to be presented in a <pre> element, so that
// line breaks and other returned whitespace is respected.
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func (rule *AlertingRule) HTMLSnippet(pathPrefix string) template.HTML {
alertMetric := model.Metric{
model.MetricNameLabel: alertMetricName,
alertNameLabel: model.LabelValue(rule.name),
}
s := fmt.Sprintf("ALERT <a href=%q>%s</a>", pathPrefix+strutil.GraphLinkForExpression(alertMetric.String()), rule.name)
s += fmt.Sprintf("\n IF <a href=%q>%s</a>", pathPrefix+strutil.GraphLinkForExpression(rule.vector.String()), rule.vector)
if rule.holdDuration > 0 {
s += fmt.Sprintf("\n FOR %s", model.Duration(rule.holdDuration))
}
if len(rule.labels) > 0 {
s += fmt.Sprintf("\n LABELS %s", rule.labels)
}
if len(rule.annotations) > 0 {
s += fmt.Sprintf("\n ANNOTATIONS %s", rule.annotations)
}
return template.HTML(s)
}