open-consul/website/pages/docs/k8s/installation/multi-cluster/kubernetes.mdx

---
layout: docs
page_title: Federation Between Kubernetes Clusters
sidebar_title: Federation Between Kubernetes Clusters
description: >-
  Federating multiple Kubernetes clusters.
---

# Federation Between Kubernetes Clusters

-> **1.8.0+:** This feature is available in Consul versions 1.8.0 and higher

~> This topic requires familiarity with [Mesh Gateways](/docs/connect/mesh-gateway) and [WAN Federation Via Mesh Gateways](/docs/connect/wan-federation-via-mesh-gateways).

-> Looking for a step-by-step guide? Please follow our Learn Guide: [Secure and Route Service Mesh Communication Across Kubernetes](https://learn.hashicorp.com/consul/kubernetes/mesh-gateways).

This page describes how to federate multiple Kubernetes clusters. See [Multi-Cluster Overview](/docs/k8s/installation/multi-cluster/overview)
for more information on use-cases and how it works.

## Primary Datacenter

Consul treats each Kubernetes cluster as a separate Consul datacenter.
In order to federate clusters, one cluster must be designated the
primary datacenter. This datacenter will be
responsible for creating the certificate authority that signs the TLS certificates
Connect uses to encrypt and authorize traffic. It also handles validating global ACL tokens. All other clusters
that are federated are considered secondaries.

#### First Time Installation

If you haven't installed Consul on your cluster, continue reading below. If you've
already installed Consul on a cluster and want to upgrade it to
support federation, see [Upgrading An Existing Cluster](#upgrading-an-existing-cluster).

You will need to use the following `config.yaml` file for your primary cluster,
with the possible modifications listed below.

```yaml
global:
  name: consul
  datacenter: dc1

  # TLS configures whether Consul components use TLS.
  tls:
    # TLS must be enabled for federation in Kubernetes.
    enabled: true

  federation:
    enabled: true
    # This will cause a Kubernetes secret to be created that
    # can be imported by secondary datacenters to configure them
    # for federation.
    createFederationSecret: true

  acls:
    manageSystemACLs: true
    # If ACLs are enabled, we must create a token for secondary
    # datacenters to replicate ACLs.
    createReplicationToken: true

  # Gossip encryption secures the protocol Consul uses to quickly
  # discover new nodes and detect failure.
  gossipEncryption:
    secretName: consul-gossip-encryption-key
    secretKey: key

connectInject:
  # Consul Connect service mesh must be enabled for federation.
  enabled: true

meshGateway:
  # Mesh gateways are gateways between datacenters. They must be enabled
  # for federation in Kubernetes since the communication between datacenters
  # goes through the mesh gateways.
  enabled: true
```

Modifications:

1. The Consul datacenter name is `dc1`. The datacenter name in each federated
   cluster **must be unique**.
1. ACLs are enabled in the above config file. They can be disabled by setting:
   ```yaml
   global:
     acls:
       manageSystemACLs: false
       createReplicationToken: false
   ```
   ACLs secure Consul by requiring every API call to present an ACL token that
   is validated to ensure it has the proper permissions. If you are only testing Consul,
   this is not required.
1. Gossip encryption is enabled in the above config file. To disable it, comment
   out or delete the `gossipEncryption` key:

   ```yaml
   global:
     # gossipEncryption:
     #   secretName: consul-gossip-encryption-key
     #   secretKey: key
   ```

   Gossip encryption encrypts the communication layer used to discover other
   nodes in the cluster and report on failure. If you are only testing Consul,
   this is not required.

   **NOTE:** This config assumes you've already
   created a Kubernetes secret called `consul-gossip-encryption-key`. See
   [the docs for this setting](/docs/k8s/helm#v-global-gossipencryption) for
   more information on how to create this secret.

1. The default mesh gateway configuration
   creates a Kubernetes Load Balancer service. If you wish to customize the
   mesh gateway, for example using a Node Port service or a custom DNS entry,
   see the [Helm reference](/docs/k8s/helm#v-meshgateway) for that setting.

With your `config.yaml` ready to go, follow our [Installation Guide](/docs/k8s/installation/overview
to install Consul on your primary cluster and then skip ahead to the [Federation Secret](#federation-secret)
section.

-> **NOTE:** You must be using consul-helm 0.21.0+. To update, run `helm repo update`.

#### Upgrading An Existing Cluster

If you have an existing cluster, you will need to upgrade it to ensure it has
the following config:

```yaml
global:
  tls:
    enabled: true
  federation:
    enabled: true
    createFederationSecret: true
  acls:
    manageSystemACLs: true
    createReplicationToken: true
meshGateway:
  enabled: true
```

1. `global.tls.enabled` must be `true`. See [Configuring TLS on an Existing Cluster](/docs/k8s/operations/tls-on-existing-cluster)
   for more information on safely upgrading a cluster to use TLS.

If you've set `enableAutoEncrypt: true`, this is also supported.

1. `global.federation.enabled` must be set to `true`. This is a new config setting.
1. If using ACLs, you'll already have `global.acls.manageSystemACLs: true`. For the
   primary cluster, you'll also need to set `global.acls.createReplicationToken: true`.
   This ensures that an ACL token is created that secondary clusters can use to authenticate
   with the primary.
1. Mesh Gateways are enabled with the default configuration. The default configuration
   creates a Kubernetes Load Balancer service. If you wish to customize the
   mesh gateway, see the [Helm reference](/docs/k8s/helm#v-meshgateway) for that setting.

With the above settings added to your existing config, follow the [Upgrading](/localhost:3000/docs/k8s/operations/upgrading)
guide to upgrade your cluster and then come back to the [Federation Secret](#federation-secret) section.

-> **NOTE:** You must be using consul-helm 0.21.0+. To update, run `helm repo update`.

## Federation Secret

The federation secret is a Kubernetes secret containing information needed
for secondary datacenters/clusters to federate with the primary. This secret is created
automatically by setting:

```yaml
global:
  federation:
    createFederationSecret: true
```

After the installation into your primary cluster you will need to export
this secret:

```shell-session
$ kubectl get secret consul-federation -o yaml > consul-federation-secret.yaml
```

!> **Security note:** The federation secret makes it possible to gain
full admin privileges in Consul. This secret must be kept securely, i.e.
it should be deleted from your filesystem after importing it to your secondary
cluster and you should use RBAC permissions to ensure only administrators
can read it from Kubernetes.

~> **Secret doesn't exist?** If you haven't set `global.name` to `consul` then the name of the secret will
be your Helm release name suffixed with `-consul-federation` e.g. `helm-release-consul-federation`.

Now you're ready to import the secret into your secondary cluster(s).

Switch `kubectl` context to your secondary Kubernetes cluster. In this example
our context for our secondary cluster is `dc2`:

```shell-session
$ kubectl config use-context dc2
Switched to context "dc2".
```

And import the secret:

```shell-session
$ kubectl apply -f consul-federation-secret.yaml
secret/consul-federation configured
```

#### Federation Secret Contents

The automatically generated federation secret contains:

- **Server certificate authority certificate** - This is the certificate authority
  used to sign Consul server-to-server communication. This is required by secondary
  clusters because they must communicate with the Consul servers in the primary cluster.
- **Server certificate authority key** - This is the signing key for the server certificate
  authority. This is required by secondary clusters because they need to create
  server certificates for each Consul server using the same certificate authority
  as the primary.

  !> **Security note:** The certificate authority key would enable an attacker to compromise Consul,
  it should be kept securely.

- **Consul server config** - This is a JSON snippet that must be used as part of the server config for secondary datacenters.
  It sets:

  - [`primary_datacenter`](/docs/agent/options.html#primary_datacenter) to the name of the primary datacenter.
  - [`primary_gateways`](/docs/agent/options.html#primary_gateways) to an array of IPs or hostnames
    for the mesh gateways in the primary datacenter. These are the addresses that
    Consul servers in secondary clusters will use to communicate with the primary
    datacenter.

    Even if there are multiple secondary datacenters, only the primary gateways
    need to be configured. Upon first connection with a primary datacenter, the
    addresses for other secondary datacenters will be discovered.

- **ACL replication token** - If ACLs are enabled, secondary datacenters need
  an ACL token in order to authenticate with the primary datacenter. This ACL
  token is also used to replicate ACLs from the primary datacenter so that
  components in each datacenter can authenticate with one another.
- **Gossip encryption key** - If gossip encryption is enabled, secondary datacenters
  need the gossip encryption key in order to be part of the gossip pool.
  Gossip is the method by which Consul discovers the addresses and health of other
  nodes.

  !> **Security note:** This gossip encryption key would enable an attacker to compromise Consul,
  it should be kept securely.

## Secondary Cluster(s)

With the primary cluster up and running, and the [federation secret](/docs/installation/multi-cluster#federation-secret) imported
into the secondary cluster, we can now install Consul into the secondary
cluster.

You will need to use the following `config.yaml` file for your secondary cluster(s),
with the possible modifications listed below.

-> **NOTE: ** You must use a separate Helm config file for each cluster (primary and secondaries) since their
settings are different.

```yaml
global:
  name: consul
  datacenter: dc2
  tls:
    enabled: true

    # Here we're using the shared certificate authority from the primary
    # datacenter that was exported via the federation secret.
    caCert:
      secretName: consul-federation
      secretKey: caCert
    caKey:
      secretName: consul-federation
      secretKey: caKey

  acls:
    manageSystemACLs: true

    # Here we're importing the replication token that was
    # exported from the primary via the federation secret.
    replicationToken:
      secretName: consul-federation
      secretKey: replicationToken

  federation:
    enabled: true
  gossipEncryption:
    secretName: consul-federation
    secretKey: gossipEncryptionKey
connectInject:
  enabled: true
meshGateway:
  enabled: true
server:
  # Here we're including the server config exported from the primary
  # via the federation secret. This config includes the addresses of
  # the primary datacenter's mesh gateways so Consul can begin federation.
  extraVolumes:
    - type: secret
      name: consul-federation
      items:
        - key: serverConfigJSON
          path: config.json
      load: true
```

Modifications:

1. The Consul datacenter name is `dc2`. The primary datacenter's name was `dc1`.
   The datacenter name in **each** federated cluster **must be unique**.
1. ACLs are enabled in the above config file. They can be disabled by removing
   the whole `acls` block:

   ```yaml
   acls:
     manageSystemACLs: false
     replicationToken:
       secretName: consul-federation
       secretKey: replicationToken
   ```

   If ACLs are enabled in one datacenter, they must be enabled in all datacenters
   because in order to communicate with that one datacenter ACL tokens are required.

1. Gossip encryption is enabled in the above config file. To disable it, don't
   set the `gossipEncryption` key:

   ```yaml
   global:
     # gossipEncryption:
     # secretName: consul-federation
     # secretKey: gossipEncryptionKey
   ```

   If gossip encryption is enabled in one datacenter, it must be enabled in all datacenters
   because in order to communicate with that one datacenter the encryption key is required.

1. The default mesh gateway configuration
   creates a Kubernetes Load Balancer service. If you wish to customize the
   mesh gateway, for example using a Node Port service or a custom DNS entry,
   see the [Helm reference](/docs/k8s/helm#v-meshgateway) for that setting.

With your `config.yaml` ready to go, follow our [Installation Guide](/docs/k8s/installation/overview)
to install Consul on your secondary cluster(s).

## Verifying Federation

To verify that both datacenters are federated, run the
`consul members -wan` command on one of the Consul server pods:

```shell-session
$ kubectl exec statefulset/consul-server -- consul members -wan
Node                 Address              Status  Type    Build     Protocol  DC   Segment
consul-server-0.dc1  10.32.4.216:8302     alive   server  1.8.0  2         dc1  <all>
consul-server-0.dc2  192.168.2.173:8302   alive   server  1.8.0  2         dc2  <all>
consul-server-1.dc1  10.32.5.161:8302     alive   server  1.8.0  2         dc1  <all>
consul-server-1.dc2  192.168.88.64:8302   alive   server  1.8.0  2         dc2  <all>
consul-server-2.dc1  10.32.1.175:8302     alive   server  1.8.0  2         dc1  <all>
consul-server-2.dc2  192.168.35.174:8302  alive   server  1.8.0  2         dc2  <all>
```

In this example (run from `dc1`), you can see that this datacenter knows about
the servers in dc2 and that they have status `alive`.

You can also use the `consul catalog services` command with the `-datacenter` flag to ensure
each datacenter can read each other's services. In this example, our `kubectl`
context is `dc1` and we're querying for the list of services in `dc2`:

```shell-session
$ kubectl exec statefulset/consul-server -- consul catalog services -datacenter dc2
consul
mesh-gateway
```

You can switch kubectl contexts and run the same command in `dc2` with the flag
`-datacenter dc1` to ensure `dc2` can communicate with `dc1`.

### Consul UI

We can also use the Consul UI to verify federation.
See [Viewing the Consul UI](docs/k8s/installation/overview#viewing-the-consul-ui)
for instructions on how to view the UI.

~> NOTE: If ACLs are enabled, your kubectl context must be in the primary datacenter
to retrieve the bootstrap token mentioned in the UI documentation.

With the UI open, you'll be able to switch between datacenters via the dropdown
in the top left:

![Consul Datacenter Dropdown](/img/consul-datacenter-dropdown.png 'Consul Datacenter Dropdown')

## Next Steps

With your Kubernetes clusters federated, try out using Consul service mesh to
route between services deployed on each cluster by following our Learn Guide: [Secure and Route Service Mesh Communication Across Kubernetes](https://learn.hashicorp.com/consul/kubernetes/mesh-gateways#deploy-microservices).

You can also read our in-depth documentation on [Consul Service Mesh In Kubernetes](/docs/k8s/connect).