consul/website/content/docs/k8s/connect/cluster-peering/tech-specs.mdx

---
layout: docs
page_title: Cluster Peering on Kubernetes Technical Specifications 
description: >- 
  In Kubernetes deployments, cluster peering connections interact with mesh gateways, exported services, and ACLs. Learn about requirements specific to k8s, including required Helm values and custom resource definitions (CRDs).
---

# 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](#helm-requirements) and [required custom resource definitions (CRDs)](#crd-requirements), as well as required Consul components and their configurations. To learn more about Consul's cluster peering feature, refer to [cluster peering overview](/consul/docs/connect/cluster-peering).

For cluster peering requirements in non-Kubernetes deployments, refer to [cluster peering technical specifications](/consul/docs/connect/cluster-peering/tech-specs).

## General requirements

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

You must also configure the following service mesh components in order to establish cluster peering connections:

- [Helm](#helm-requirements)
- [Custom resource definitions (CRD)](#crd-requirements)
- [Mesh gateways](#mesh-gateway-requirements)
- [Exported services](#exported-service-requirements)
- [ACLs](#acl-requirements)

## Helm specifications

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. The following values must be set in the Helm chart to enable mesh gateways:

- [`global.tls.enabled = true`](/consul/docs/k8s/helm#v-global-tls-enabled)
- [`meshGateway.enabled = true`](/consul/docs/k8s/helm#v-meshgateway-enabled)

Refer to the following example Helm configuration:

<CodeBlockConfig filename="values.yaml">

```yaml
global:
  name: consul
  image: "hashicorp/consul:1.16.0"
  peering:
    enabled: true
  tls:
    enabled: true
meshGateway:
  enabled: true
```

</CodeBlockConfig>

After mesh gateways are enabled in the Helm chart, you can separately [configure Mesh CRDs](#mesh-gateway-configuration-for-kubernetes).

## CRD specifications

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:

<CodeTabs tabs={[ "PeeringAcceptor", "PeeringDialer" ]}>

<CodeBlockConfig filename="acceptor.yaml">

```yaml
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"
```

</CodeBlockConfig>

<CodeBlockConfig filename="dialer.yaml">

```yaml
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"
```

</CodeBlockConfig>
</CodeTabs>

## 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:

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

  <CodeBlockConfig filename="mesh.yaml">

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

  </CodeBlockConfig>

1. Apply the mesh CRD to `cluster-01`.

  ```shell-session
  $ kubectl --context $CLUSTER1_CONTEXT apply -f mesh.yaml 
  ```

1. Apply the mesh CRD to `cluster-02`.

  ```shell-session
  $  kubectl --context $CLUSTER2_CONTEXT apply -f mesh.yaml 
  ```

<Note>

  For help setting up the cluster context variables used in this example, refer to [assign cluster IDs to environmental variables](/consul/docs/k8s/connect/cluster-peering/usage/establish-peering#assign-cluster-ids-to-environmental-variables).

</Note>

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

- A Consul 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. For additional Envoy proxy configuration information, refer to [Gateway options](/consul/docs/connect/proxies/envoy#gateway-options) and [Escape-hatch overrides](/consul/docs/connect/proxies/envoy#escape-hatch-overrides).

### Mesh gateway modes

By default, all cluster peering connections use mesh gateways in [remote mode](/consul/docs/connect/gateways/mesh-gateway/service-to-service-traffic-wan-datacenters#remote). 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.

To learn how to change the mesh gateway mode to `local` on your Kubernetes deployment, refer to [configure the mesh gateway mode for traffic between services](/consul/docs/k8s/connect/cluster-peering/usage/establish-peering#configure-the-mesh-gateway-mode-for-traffic-between-services).

## Exported service specifications

The `exported-services` CRD 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](/consul/docs/k8s/connect/cluster-peering/usage/establish-peering#export-services-between-clusters).

Refer to [`exported-services` configuration entry](/consul/docs/connect/config-entries/exported-services) 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.