Cluster peering technical specifications

This reference topic describes the technical specifications associated with using cluster peering in your deployments. These specifications include required Consul components and their configurations. To learn more about Consul's cluster peering feature, refer to cluster peering overview.

For cluster peering requirements in Kubernetes deployments, refer to cluster peering on Kubernetes technical specifications.

Requirements

Consul's default configuration supports cluster peering connections directly between clusters. In production environments, we recommend using mesh gateways to securely route service mesh traffic between partitions with cluster peering connections.

In addition, make sure your Consul environment meets the following prerequisites:

Consul v1.14 or higher.
Use Envoy proxies. Envoy is the only proxy with mesh gateway capabilities in Consul.
A local Consul agent is required to manage mesh gateway configurations.

Mesh gateway specifications

To change Consul's default configuration and enable cluster peering through mesh gateways, use a mesh configuration entry to update your network's service mesh proxies globally:

In a mesh configuration entry, set PeerThroughMeshGateways to true:
mesh-config.hcl
```
Kind = "mesh"
Peering {
  PeerThroughMeshGateways = true
}
```
Write the configuration entry to Consul:
```
$ consul config write mesh-config.hcl
```

When cluster peering through mesh gateways, consider the following deployment requirements:

A cluster requires a registered mesh gateway in order to export services to peers in other regions or cloud providers.
The mesh gateway must also be registered in the same admin partition as the exported services and their exported-services configuration entry. An enterprise license is required to use multiple admin partitions with a single cluster of Consul servers.
To use the local mesh gateway mode, you must register a mesh gateway in the importing cluster.
Define the Proxy.Config settings using opaque parameters compatible with your proxy. Refer to the Gateway options and Escape-hatch Overrides documentation for additional Envoy proxy configuration information.

Mesh gateway modes

By default, cluster peering connections use mesh gateways in remote mode. Be aware of these additional requirements when changing a mesh gateway's mode.

For mesh gateways that connect peered clusters, you can set the mode as either remote or local.
The none mode is invalid for mesh gateways with cluster peering connections.

Refer to mesh gateway modes for more information.

Sidecar proxy specifications

The Envoy proxies that function as sidecars in your service mesh require configuration in order to properly route traffic to peers. Sidecar proxies are defined in the service definition.

Configure the proxy.upstreams parameters to route traffic to the correct service, namespace, and peer. Refer to the upstreams documentation for details.
The proxy.upstreams.destination_name parameter is always required.
The proxy.upstreams.destination_peer parameter must be configured to enable cross-cluster traffic.
The proxy.upstream/destination_namespace configuration is only necessary if the destination service is in a non-default namespace.

Exported service specifications

The exported-services configuration entry is required in order for services to communicate across partitions with cluster peering connections. Basic guidance on using the exported-services configuration entry is included in Establish cluster peering connections.

Refer to the exported-services configuration entry reference for more information.

ACL specifications

If ACLs are enabled, you must add tokens to grant the following permissions:

Grant service:write permissions to services that define mesh gateways in their server definition.
Grant service:read permissions for all services on the partition.
Grant mesh:write permissions to the mesh gateways that participate in cluster peering connections. This permission allows a leaf certificate to be issued for mesh gateways to terminate TLS sessions for HTTP requests.