Add support for updating existing Slack messages

.gitignore

@@ -14,6 +14,7 @@
 !/cluster/testdata/*.yml
 !/config/testdata/*.yml
 !/examples/ha/tls/*.yml
+!/examples/slack-update-messages.yml
 !/notify/email/testdata/*.yml
 !/doc/examples/simple.yml
 !/circle.yml

config/notifiers.go

@@ -522,6 +522,9 @@ type SlackConfig struct {
 	LinkNames   bool           `yaml:"link_names" json:"link_names,omitempty"`
 	MrkdwnIn    []string       `yaml:"mrkdwn_in,omitempty" json:"mrkdwn_in,omitempty"`
 	Actions     []*SlackAction `yaml:"actions,omitempty" json:"actions,omitempty"`
+	// UpdateMessage enables updating existing Slack messages instead of creating new ones.
+	// Requires bot token with chat:write scope. Webhook URLs do not support updates.
+	UpdateMessage bool `yaml:"update_message" json:"update_message,omitempty"`
 	// Timeout is the maximum time allowed to invoke the slack. Setting this to 0
 	// does not impose a timeout.
 	Timeout time.Duration `yaml:"timeout" json:"timeout"`

examples/slack-update-messages.yml

@@ -0,0 +1,37 @@
+# Alertmanager configuration with Slack message updates
+global:
+  resolve_timeout: 5m
+
+# Route configuration - required!
+route:
+  receiver: 'slack'
+  group_by: ['alertname', 'cluster', 'service']
+  group_wait: 10s
+  group_interval: 10s
+  repeat_interval: 12h
+
+receivers:
+  - name: 'slack'
+    slack_configs:
+      - send_resolved: true # Required for message updates!
+        api_url: 'https://slack.com/api/chat.postMessage'
+        http_config:
+          authorization:
+            credentials: 'xoxb-your-bot-token'
+        channel: '#your-channel'
+        update_message: true  # This enables message updates!
+
+        # Template for updated messages
+        title: '{{ .GroupLabels.alertname }} - {{ .Status | toUpper }}'
+        text: |
+          {{ if eq .Status "firing" }}
+          🔥 *{{ .Alerts.Firing | len }} alert(s) firing*
+          {{ else }}
+          ✅ *All alerts resolved*
+          {{ end }}
+
+          {{ range .Alerts }}
+          • {{ if .Annotations.summary }}{{ .Annotations.summary }}{{ else }}{{ .Labels.alertname }}{{ end }}
+          {{ end }}
+
+        color: '{{ if eq .Status "firing" }}danger{{ else }}good{{ end }}'

nflog/nflogpb/nflog.proto

@@ -39,6 +39,9 @@ message Entry {
   repeated uint64 firing_alerts = 6;
   // ResolvedAlerts list of hashes of resolved alerts at the last notification time.
   repeated uint64 resolved_alerts = 7;
+  // Metadata holds integration-specific metadata (e.g. Slack message_ts, Jira issue key).
+  // This allows integrations to store identifiers for updating existing notifications.
+  map<string, string> metadata = 8;
 }
 
 // MeshEntry is a wrapper message to communicate a notify log

notify/metadata_store.go

@@ -0,0 +1,81 @@
+// Copyright 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 notify
+
+import (
+	"fmt"
+	"sync"
+
+	"github.com/prometheus/alertmanager/nflog/nflogpb"
+)
+
+// MetadataStore is a temporary in-memory store for notification metadata
+// (e.g., Slack message_ts, Jira issue keys) until protobuf Entry supports metadata field.
+// This allows integrations to update existing notifications instead of creating new ones.
+type MetadataStore struct {
+	mtx  sync.RWMutex
+	data map[string]map[string]string // key: stateKey(groupKey, receiver) -> metadata map
+}
+
+// NewMetadataStore creates a new MetadataStore.
+func NewMetadataStore() *MetadataStore {
+	return &MetadataStore{
+		data: make(map[string]map[string]string),
+	}
+}
+
+// Set stores metadata for a given receiver and group key.
+func (s *MetadataStore) Set(receiver *nflogpb.Receiver, groupKey string, metadata map[string]string) {
+	s.mtx.Lock()
+	defer s.mtx.Unlock()
+
+	key := stateKey(groupKey, receiver)
+	s.data[key] = metadata
+}
+
+// Get retrieves metadata for a given receiver and group key.
+func (s *MetadataStore) Get(receiver *nflogpb.Receiver, groupKey string) (map[string]string, bool) {
+	s.mtx.RLock()
+	defer s.mtx.RUnlock()
+
+	key := stateKey(groupKey, receiver)
+	metadata, ok := s.data[key]
+	return metadata, ok
+}
+
+// Delete removes metadata for a given receiver and group key.
+func (s *MetadataStore) Delete(receiver *nflogpb.Receiver, groupKey string) {
+	s.mtx.Lock()
+	defer s.mtx.Unlock()
+
+	key := stateKey(groupKey, receiver)
+	delete(s.data, key)
+}
+
+// stateKey returns a string key for a log entry consisting of the group key and receiver.
+// This matches the key generation in nflog.
+func stateKey(gkey string, r *nflogpb.Receiver) string {
+	return receiverKey(gkey, r)
+}
+
+// receiverKey creates a unique key from group key and receiver.
+// Format matches nflog's internal stateKey format: "groupKey:groupName/integration/idx".
+func receiverKey(groupKey string, r *nflogpb.Receiver) string {
+	return groupKey + ":" + receiverString(r)
+}
+
+// receiverString returns a string representation of the receiver.
+func receiverString(r *nflogpb.Receiver) string {
+	return fmt.Sprintf("%s/%s/%d", r.GroupName, r.Integration, r.Idx)
+}