---
layout: docs
page_title: Single Consul Datacenter in Multiple Kubernetes Clusters - Kubernetes
description: Single Consul Datacenter deployed in multiple Kubernetes clusters
---

# Single Consul Datacenter in Multiple Kubernetes Clusters

-> Requires consul-helm v0.32.1 or higher.

This page describes how to deploy a single Consul datacenter in multiple Kubernetes clusters,
with both servers and clients running in one cluster, and only clients running in the rest of the clusters.
In this example, we will use two Kubernetes clusters, but this approach could be extended to using more than two.

~> **Note:** This deployment topology requires that your Kubernetes clusters have a flat network
for both pods and nodes, so that pods or nodes from one cluster can connect
to pods or nodes in another.

## Deploying Consul servers and clients in the first cluster

First, we will deploy the Consul servers with Consul clients in the first cluster.
For that, we will use the following Helm configuration:

<CodeBlockConfig filename="cluster1-config.yaml">

```yaml
global:
  datacenter: dc1
  tls:
    enabled: true
    enableAutoEncrypt: true
  acls:
    manageSystemACLs: true
  gossipEncryption:
    secretName: consul-gossip-encryption-key
    secretKey: key
connectInject:
  enabled: true
controller:
  enabled: true
ui:
  service:
    type: NodePort
```

</CodeBlockConfig>

Note that we are deploying in a secure configuration, with gossip encryption,
TLS for all components, and ACLs. We are enabling the Consul Service Mesh and the controller for CRDs
so that we can use them to later verify that our services can connect with each other across clusters.

We're also setting UI's service type to be `NodePort`.
This is needed so that we can connect to servers from another cluster without using the pod IPs of the servers,
which are likely going to change.

To deploy, first we need to generate the Gossip encryption key and save it as a Kubernetes secret.

```shell
$ kubectl create secret generic consul-gossip-encryption-key --from-literal=key=$(consul keygen)
```

Now we can install our Consul cluster with Helm:
```shell
$ helm install cluster1 -f cluster1-config.yaml hashicorp/consul
```

~> **Note:** The Helm release name must be unique for each Kubernetes cluster.
That is because the Helm chart will use the Helm release name as a prefix for the
ACL resources that it creates, such as tokens and auth methods. If the names of the Helm releases
are the same, the Helm installation in subsequent clusters will clobber existing ACL resources.

Once the installation finishes and all components are running and ready,
we need to extract the gossip encryption key we've created, the CA certificate
and the ACL bootstrap token generated during installation,
so that we can apply them to our second Kubernetes cluster.

```shell
kubectl get secret consul-gossip-encryption-key cluster1-consul-ca-cert cluster1-consul-bootstrap-acl-token -o yaml > cluster1-credentials.yaml
```

## Deploying Consul clients in the second cluster
~> **Note:** If multiple Kubernetes clusters will be joined to the Consul Datacenter, then the following instructions will need to be repeated for each additional Kubernetes cluster.

Now we can switch to the second Kubernetes cluster where we will deploy only the Consul clients
that will join the first Consul cluster.

First, we need to apply credentials we've extracted from the first cluster to the second cluster:

```shell
$ kubectl apply -f cluster1-credentials.yaml
```
To deploy in the second cluster, we will use the following Helm configuration:

<CodeBlockConfig filename="cluster2-config.yaml" highlight="6-11,15-17">

```yaml
global:
  enabled: false
  datacenter: dc1
  acls:
    manageSystemACLs: true
    bootstrapToken:
      secretName: cluster1-consul-bootstrap-acl-token
      secretKey: token
  gossipEncryption:
    secretName: consul-gossip-encryption-key
    secretKey: key
  tls:
    enabled: true
    enableAutoEncrypt: true
    caCert:
      secretName: cluster1-consul-ca-cert
      secretKey: tls.crt
externalServers:
  enabled: true
  # This should be any node IP of the first k8s cluster
  hosts: ["10.0.0.4"]
  # The node port of the UI's NodePort service
  httpsPort: 31557
  tlsServerName: server.dc1.consul
  # The address of the kube API server of this Kubernetes cluster
  k8sAuthMethodHost: https://kubernetes.example.com:443
client:
  enabled: true
  join: ["provider=k8s kubeconfig=/consul/userconfig/cluster1-kubeconfig/kubeconfig label_selector=\"app=consul,component=server\""]
  extraVolumes:
    - type: secret
      name: cluster1-kubeconfig
      load: false
connectInject:
  enabled: true
```

</CodeBlockConfig>

Note that we're referencing secrets from the first cluster in ACL, gossip, and TLS configuration.

Next, we need to set up the `externalServers` configuration.

The `externalServers.hosts` and `externalServers.httpsPort`
refer to the IP and port of the UI's NodePort service deployed in the first cluster.
Set the `externalServers.hosts` to any Node IP of the first cluster,
which you can see by running `kubectl get nodes -o wide`.
Set `externalServers.httpsPort` to the `nodePort` of the `cluster1-consul-ui` service.
In our example, the port is `31557`.

```shell
$ kubectl get service cluster1-consul-ui --context cluster1
NAME                 TYPE       CLUSTER-IP    EXTERNAL-IP   PORT(S)         AGE
cluster1-consul-ui   NodePort   10.0.240.80   <none>        443:31557/TCP   40h
```

We set the `externalServer.tlsServerName` to `server.dc1.consul`. This the DNS SAN
(Subject Alternative Name) that is present in the Consul server's certificate.
We need to set it because we're connecting to the Consul servers over the node IP,
but that IP isn't present in the server's certificate.
To make sure that the hostname verification succeeds during the TLS handshake, we need to set the TLS
server name to a DNS name that *is* present in the certificate.

Next, we need to set `externalServers.k8sAuthMethodHost` to the address of the second Kubernetes API server.
This should be the address that is reachable from the first cluster, and so it cannot be the internal DNS
available in each Kubernetes cluster. Consul needs it so that `consul login` with the Kubernetes auth method will work
from the second cluster.
More specifically, the Consul server will need to perform the verification of the Kubernetes service account
whenever `consul login` is called, and to verify service accounts from the second cluster it needs to
reach the Kubernetes API in that cluster.
The easiest way to get it is to set it from your `kubeconfig` by running `kubectl config view` and grabbing
the value of `cluster.server` for the second cluster.

Lastly, we need to set up the clients so that they can discover the servers in the first cluster.
For this, we will use Consul's cloud auto-join feature
for the [Kubernetes provider](https://www.consul.io/docs/install/cloud-auto-join#kubernetes-k8s).
To use it we need to provide a way for the Consul clients to reach the first Kubernetes cluster.
To do that, we need to save the `kubeconfig` for the first cluster as a Kubernetes secret in the second cluster
and reference it in the `clients.join` value. Note that we're making that secret available to the client pods
by setting it in `client.extraVolumes`.

~> **Note:** The kubeconfig you're providing to the client should have minimal permissions.
The cloud auto-join provider will only need permission to read pods.
Please see [Kubernetes Cloud auto-join](https://www.consul.io/docs/install/cloud-auto-join#kubernetes-k8s)
for more details.

Now we're ready to install!

```shell
helm install cluster2 -f cluster2-config.yaml hashicorp/consul
```

## Verifying the Consul Service Mesh works

~> When Transparent proxy is enabled, services in one Kubernetes cluster that need to communicate with a service in another Kubernetes cluster must have a explicit upstream configured through the ["consul.hashicorp.com/connect-service-upstreams"](https://www.consul.io/docs/k8s/connect#consul-hashicorp-com-connect-service-upstreams) annotation.

Now that we have our Consul cluster in multiple k8s clusters up and running, we will
deploy two services and verify that they can connect to each other.

First, we'll deploy `static-server` service in the first cluster:

<CodeBlockConfig filename="static-server.yaml">

```yaml
---
apiVersion: consul.hashicorp.com/v1alpha1
kind: ServiceIntentions
metadata:
  name: static-server
spec:
  destination:
    name: static-server
  sources:
    - name: static-client
      action: allow
---
apiVersion: v1
kind: Service
metadata:
  name: static-server
spec:
  type: ClusterIP
  selector:
    app: static-server
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: static-server
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: static-server
spec:
  replicas: 1
  selector:
    matchLabels:
      app: static-server
  template:
    metadata:
      name: static-server
      labels:
        app: static-server
      annotations:
        "consul.hashicorp.com/connect-inject": "true"
    spec:
      containers:
        - name: static-server
          image: hashicorp/http-echo:latest
          args:
            - -text="hello world"
            - -listen=:8080
          ports:
            - containerPort: 8080
              name: http
      serviceAccountName: static-server
```

</CodeBlockConfig>

Note that we're defining a Service intention so that our services are allowed to talk to each other.

Then we'll deploy `static-client` in the second cluster with the following configuration:

<CodeBlockConfig filename="static-client.yaml">

```yaml
apiVersion: v1
kind: Service
metadata:
  name: static-client
spec:
  selector:
    app: static-client
  ports:
    - port: 80
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: static-client
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: static-client
spec:
  replicas: 1
  selector:
    matchLabels:
      app: static-client
  template:
    metadata:
      name: static-client
      labels:
        app: static-client
      annotations:
        "consul.hashicorp.com/connect-inject": "true"
        "consul.hashicorp.com/connect-service-upstreams": "static-server:1234"
    spec:
      containers:
        - name: static-client
          image: curlimages/curl:latest
          command: [ "/bin/sh", "-c", "--" ]
          args: [ "while true; do sleep 30; done;" ]
      serviceAccountName: static-client
```

</CodeBlockConfig>

Once both services are up and running, we can connect to the `static-server` from `static-client`:

```shell
$ kubectl exec deploy/static-client -- curl -s localhost:1234
"hello world"
```
