feat: add basic support for multi-cluster replication

README.md

@@ -88,8 +88,8 @@ Please note this table only reports end-to-end tests suite coverage, others vers
 - [x] Cluster monitoring.
 - [x] Complete end2end test suite.
 - [x] Archival.
+- [x] Multi cluster replication.
 - [ ] Auto scaling.
-- [ ] Multi cluster replication.
 
 ## Contributing
 

api/v1beta1/temporalcluster_types.go

@@ -799,6 +799,11 @@ func (s *ClusterArchivalSpec) IsEnabled() bool {
 	return s != nil && s.Enabled
 }
 
+type ClusterReplicationSpec struct {
+	EnableGlobalNamespace  bool  `json:"enableGlobalNamespace"`
+	InitialFailoverVersion int64 `json:"initialFailoverVersion"`
+}
+
 type ArchivalProviderKind string
 
 const (
@@ -956,6 +961,8 @@ type TemporalClusterSpec struct {
 	// Archival allows Workflow Execution Event Histories and Visibility data backups for the temporal cluster.
 	// +optional
 	Archival *ClusterArchivalSpec `json:"archival,omitempty"`
+
+	Replication *ClusterReplicationSpec `json:"replication,omitempty"`
 }
 
 // ServiceStatus reports a service status.

bundle/manifests/temporal.io_temporalclusters.yaml

@@ -2584,6 +2584,17 @@ spec:
                 - defaultStore
                 - visibilityStore
                 type: object
+              replication:
+                properties:
+                  enableGlobalNamespace:
+                    type: boolean
+                  initialFailoverVersion:
+                    format: int64
+                    type: integer
+                required:
+                - enableGlobalNamespace
+                - initialFailoverVersion
+                type: object
               services:
                 description: Services allows customizations for each temporal services
                   deployment.

config/crd/bases/temporal.io_temporalclusters.yaml

@@ -2004,6 +2004,17 @@ spec:
                     - defaultStore
                     - visibilityStore
                   type: object
+                replication:
+                  properties:
+                    enableGlobalNamespace:
+                      type: boolean
+                    initialFailoverVersion:
+                      format: int64
+                      type: integer
+                  required:
+                    - enableGlobalNamespace
+                    - initialFailoverVersion
+                  type: object
                 services:
                   description: Services allows customizations for each temporal services deployment.
                   properties:

docs/features/multi-cluster-replication.md

@@ -0,0 +1,62 @@
+# Multi-cluster replication
+
+Temporal supports multi-cluster replication. This feature allows you to replicate specific temporal namespaces to a different temporal cluster. This is useful for disaster recovery, or to have a temporal cluster in a different region for latency reasons, or if you want to upgrade the temporal history shard count.
+
+## How it works
+
+To set up multi-cluster replication using the temporal operator, you must first enable global namespaces on the clusters you wish to support, and then assign them a unique failover version.
+This can be configured via the `spec.replicaton` of the `TemporalCluster` resource. Temporal operator automatically configures the remaining fields, and currently hard-codes the failover
+increment to 100. If a cluster fails, the remaining clusters will elect a new primary cluster based with the lowest failover version. The original cluster, if it comes back online, will
+be assigned a new failover version, which is always the lowest multiple of the failover increment (+ initialFailoverVersion) that is greater than the leader cluster's failover version.
+
+```yaml
+apiVersion: temporal.io/v1beta1
+kind: TemporalCluster
+metadata:
+  name: prod
+spec:
+  replication:
+    enableGlobalNamespace: true
+    initialFailoverVersion: 1
+```
+
+## Starting replication
+
+Once the two clusters are configured, simply set up connections between them using the temporal CLI. In the future, there may be a way to do this via the operator.
+
+```bash
+# port forward to the frontend of the primary cluster
+kubectl port-forward primary-frontend 7233:7233
+
+temporal operator cluster upsert --frontend-address secondary-cluster.namespace.svc.cluster.local:7233 --enable-connection true
+
+# port forward to the frontend of the secondary cluster
+kubectl port-forward secondary-frontend 7233:7233
+
+tepmoral operator cluster upsert --frontend-address primary-cluster.namespace.svc.cluster.local:7233 --enable-connection true
+```
+
+## Replicating namespaces
+
+Once the clusters are connected, you can replicate namespaces between them. This can be done via the temporal CLI, or via the operator. Simply create a new namespace resource for just the primary clusterRef, and add the secondary cluster to the list of clusters. The namespace will be added to the secondary cluster automatically, with all the same settings, and start receiving updates.
+
+```yaml
+apiVersion: temporal.io/v1beta1
+kind: TemporalNamespace
+metadata:
+  name: primary-namespace
+spec:
+  clusterRef:
+    name: primary
+  clusters:
+    - primary
+    - secondary
+  activeClusterName: secondary
+  isGlobalNamespace: true
+```
+
+## A mechanism for increasing the history shard count
+
+Since temporal 1.20, replicated clusters do not require the same number of history shards. This means it is a viable method for migrating a cluster that has outgrown its shard count. To do this, simply have your secondary cluster use a higher shard count than the primary cluster. The only requirement is that the shard count on the secondary cluster is an even multiple of the first. So if you have 512 shards on the primary cluster, you can have 1024 shards (or any other multiple) on the secondary cluster, but not 1023.
+
+When replication is complete, simply take down the old cluster, and flip your clients over to the new cluster. This can all be achieved with very little downtime.

internal/resource/config/configmap_builder.go

@@ -197,6 +197,33 @@ func (b *ConfigmapBuilder) buildArchivalConfig() (*config.Archival, *config.Arch
 	return cfg, namespaceDefaults, nil
 }
 
+func (b *ConfigmapBuilder) buildClusterMetadataConfig() (*cluster.Config, error) {
+	var failoverVersion int64 = 0
+	if b.instance.Spec.Replication != nil {
+		failoverVersion = b.instance.Spec.Replication.InitialFailoverVersion
+	}
+	enableGlobalNamespace := false
+	if b.instance.Spec.Replication != nil {
+		enableGlobalNamespace = b.instance.Spec.Replication.EnableGlobalNamespace
+	}
+
+	cfg := &cluster.Config{
+		EnableGlobalNamespace:    enableGlobalNamespace,
+		FailoverVersionIncrement: 10,
+		MasterClusterName:        b.instance.Name,
+		CurrentClusterName:       b.instance.Name,
+		ClusterInformation: map[string]cluster.ClusterInformation{
+			b.instance.Name: {
+				Enabled:                true,
+				InitialFailoverVersion: failoverVersion,
+				RPCAddress:             "127.0.0.1:7233",
+			},
+		},
+	}
+
+	return cfg, nil
+}
+
 func (b *ConfigmapBuilder) Update(object client.Object) error {
 	configMap := object.(*corev1.ConfigMap)
 
@@ -210,6 +237,11 @@ func (b *ConfigmapBuilder) Update(object client.Object) error {
 		return fmt.Errorf("can't build archival config: %w", err)
 	}
 
+	clusterMetadata, err := b.buildClusterMetadataConfig()
+	if err != nil {
+		return fmt.Errorf("can't build cluster metadata config: %w", err)
+	}
+
 	temporalCfg := config.Config{
 		Global: config.Global{
 			Membership: config.Membership{
@@ -223,19 +255,7 @@ func (b *ConfigmapBuilder) Update(object client.Object) error {
 		NamespaceDefaults: config.NamespaceDefaults{
 			Archival: *archivalNamespaceDefaults,
 		},
-		ClusterMetadata: &cluster.Config{
-			EnableGlobalNamespace:    false,
-			FailoverVersionIncrement: 10,
-			MasterClusterName:        b.instance.Name,
-			CurrentClusterName:       b.instance.Name,
-			ClusterInformation: map[string]cluster.ClusterInformation{
-				b.instance.Name: {
-					Enabled:                true,
-					InitialFailoverVersion: 1,
-					RPCAddress:             "127.0.0.1:7233",
-				},
-			},
-		},
+		ClusterMetadata: clusterMetadata,
 		Services: map[string]config.Service{
 			string(primitives.FrontendService): {
 				RPC: config.RPC{