Cluster peering on Kubernetes technical specifications

This reference topic describes the technical specifications associated with using cluster peering in your Kubernetes deployments. These specifications include required Helm values and required custom resource definitions (CRDs), as well as required Consul components and their configurations.

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

General Requirements

To use cluster peering features, make sure your Consul environment meets the following prerequisites:

Consul v1.14 or higher
Consul on Kubernetes v1.0.0 or higher
At least two Kubernetes clusters

In addition, the following service mesh components are required in order to establish cluster peering connections:

Helm requirements

Mesh gateways are required when establishing cluster peering connections. The following values must be set in the Helm chart to enable mesh gateways:

Refer to the following example Helm configuration:

global:
  name: consul
  image: "hashicorp/consul:1.14.1"
  peering:
    enabled: true
  tls:
    enabled: true
meshGateway:
  enabled: true

After mesh gateways are enabled in the Helm chart, you can separately configure Mesh CRDs.

CRD requirements

You must create the following CRDs in order to establish a peering connection:

PeeringAcceptor: Generates a peering token and accepts an incoming peering connection.
PeeringDialer: Uses a peering token to make an outbound peering connection with the cluster that generated the token.

Refer to the following example CRDs:

apiVersion: consul.hashicorp.com/v1alpha1
kind: PeeringAcceptor
metadata:
  name: cluster-02 ## The name of the peer you want to connect to
spec:
  peer:
    secret:
      name: "peering-token"
      key: "data"
      backend: "kubernetes"

apiVersion: consul.hashicorp.com/v1alpha1
kind: PeeringDialer
metadata:
  name: cluster-01 ## The name of the peer you want to connect to
spec:
  peer:
    secret:
      name: "peering-token"
      key: "data"
      backend: "kubernetes"

Mesh gateway requirements

Mesh gateways are required for routing service mesh traffic between partitions with cluster peering connections. Consider the following general requirements for mesh gateways when using cluster peering:

A cluster requires a registered mesh gateway in order to export services to peers.
For Enterprise, this mesh gateway must also be registered in the same partition as the exported services and their exported-services configuration entry.
To use the local mesh gateway mode, you must register a mesh gateway in the importing cluster.

In addition, you must 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, all 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.

Mesh gateway configuration for Kubernetes

Mesh gateways are required for cluster peering connections. Complete the following steps to add mesh gateways to your deployment so that you can establish cluster peering connections:

In cluster-01 create the Mesh custom resource with peeringThroughMeshGateways set to true.

apiVersion: consul.hashicorp.com/v1alpha1
kind: Mesh
metadata:
  name: mesh
spec:
  peering:
    peerThroughMeshGateways: true

Apply the mesh gateway to cluster-01. Replace CLUSTER1_CONTEXT to target the first Consul cluster.
```
$ kubectl --context $CLUSTER1_CONTEXT apply -f mesh.yaml 
```

Repeat the process to create and apply a mesh gateway with cluster peering enabled to cluster-02. Replace CLUSTER2_CONTEXT to target the second Consul cluster.

apiVersion: consul.hashicorp.com/v1alpha1
kind: Mesh
metadata:
  name: mesh
spec:
  peering:
    peerThroughMeshGateways: true

$  kubectl --context $CLUSTER2_CONTEXT apply -f mesh.yaml

Exported service requirements

The exported-services CRD is required in order for services to communicate across partitions with cluster peering connections.

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

ACL requirements

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.