---
layout: docs
page_title: Federation Between VMs and Kubernetes
description: >-
  Federating Kubernetes clusters and VMs.
---

# Federation Between VMs and Kubernetes

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

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

Consul datacenters running on non-kubernetes platforms like VMs or bare metal can
be federated with Kubernetes datacenters. Just like with Kubernetes, one datacenter
must be the [primary](/docs/k8s/installation/multi-cluster/kubernetes#primary-datacenter).

## Kubernetes as the Primary

If your primary datacenter is running on Kubernetes, use the Helm config from the
[Primary Datacenter](/docs/k8s/installation/multi-cluster/kubernetes#primary-datacenter) section to install Consul.

Once installed on Kubernetes, and with the `ProxyDefaults` [resource created](/docs/k8s/installation/multi-cluster/kubernetes#proxydefaults),
you'll need to export the following information from the primary Kubernetes cluster:

- Certificate authority cert and key (in order to create SSL certs for VMs)
- External addresses of Kubernetes mesh gateways
- Replication ACL token
- Gossip encryption key

The following sections detail how to export this data.

### Certificates

1. Retrieve the certificate authority cert:

   ```sh
   kubectl get secrets/consul-ca-cert --namespace consul --template='{{index .data "tls.crt" | base64decode }}' > consul-agent-ca.pem
   ```

1. And the certificate authority signing key:

   ```sh
   kubectl get secrets/consul-ca-key --namespace consul --template='{{index .data "tls.key" | base64decode }}' > consul-agent-ca-key.pem
   ```

1. With the `consul-agent-ca.pem` and `consul-agent-ca-key.pem` files you can
   create certificates for your servers and clients running on VMs that share the
   same certificate authority as your Kubernetes servers.

   You can use the `consul tls` commands to generate those certificates:

   ```sh
   # NOTE: consul-agent-ca.pem and consul-agent-ca-key.pem must be in the current
   # directory.
   $ consul tls cert create -server -dc=vm-dc -node <node_name>
   ==> WARNING: Server Certificates grants authority to become a
       server and access all state in the cluster including root keys
       and all ACL tokens. Do not distribute them to production hosts
       that are not server nodes. Store them as securely as CA keys.
   ==> Using consul-agent-ca.pem and consul-agent-ca-key.pem
   ==> Saved vm-dc-server-consul-0.pem
   ==> Saved vm-dc-server-consul-0-key.pem
   ```

   -> Note the `-node` option in the above command. This should be same as the node name of the [Consul Agent](/docs/agent#running-an-agent). This is a [requirement](/docs/connect/gateways/mesh-gateway/wan-federation-via-mesh-gateways#tls) for Consul Federation to work. Alternatively, if you plan to use the same certificate and key pair on all your Consul server nodes, or you don't know the nodename in advance, use `-node "*"` instead.
   Not satisfying this requirement would result in the following error in the Consul Server logs:
   `[ERROR] agent.server.rpc: TLS handshake failed: conn=from= error="remote error: tls: bad certificate"`

   See the help for output of `consul tls cert create -h` to see more options
   for generating server certificates.

1. These certificates can be used in your server config file:

   <CodeBlockConfig filename="server.hcl">

   ```hcl
   tls {
     defaults {
       cert_file = "vm-dc-server-consul-0.pem"
       key_file = "vm-dc-server-consul-0-key.pem"
       ca_file = "consul-agent-ca.pem"
     }
   }
   ```

   </CodeBlockConfig>

1. For clients, you can generate TLS certs with:

   ```shell-session
   $ consul tls cert create -client
   ==> Using consul-agent-ca.pem and consul-agent-ca-key.pem
   ==> Saved dc1-client-consul-0.pem
   ==> Saved dc1-client-consul-0-key.pem
   ```

   Or use the [auto_encrypt](/docs/agent/config/config-files#auto_encrypt) feature.

### Mesh Gateway Addresses

Retrieve the WAN addresses of the mesh gateways:

```shell-session
$ kubectl exec statefulset/consul-server --namespace consul -- sh -c \
  'curl --silent --insecure https://localhost:8501/v1/catalog/service/mesh-gateway | jq ".[].ServiceTaggedAddresses.wan"'
{
  "Address": "1.2.3.4",
  "Port": 443
}
{
  "Address": "1.2.3.4",
  "Port": 443
}
```

In this example, the addresses are the same because both mesh gateway pods are
fronted by the same Kubernetes load balancer.

These addresses will be used in the server config for the `primary_gateways`
setting:

```hcl
primary_gateways = ["1.2.3.4:443"]
```

### Replication ACL Token

If ACLs are enabled, you'll also need the replication ACL token:

```shell-session
$ kubectl get secrets/consul-acl-replication-acl-token --namespace consul --template='{{.data.token | base64decode}}'
e7924dd1-dc3f-f644-da54-81a73ba0a178
```

This token will be used in the server config for the replication token.

```hcl
acls {
  tokens {
    replication = "e7924dd1-dc3f-f644-da54-81a73ba0a178"
  }
}
```

-> **NOTE:** You'll also need to set up additional ACL tokens as needed by the
ACL system. See tutorial [Secure Consul with Access Control Lists (ACLs)](https://learn.hashicorp.com/tutorials/consul/access-control-setup-production#apply-individual-tokens-to-agents)
for more information.

### Gossip Encryption Key

If gossip encryption is enabled, you'll need the key as well. The command
to retrieve the key will depend on which Kubernetes secret you've stored it in.

This key will be used in server and client configs for the `encrypt` setting:

```hcl
encrypt = "uF+GsbI66cuWU21kiXLze5JLEX5j4iDFlDTb0ZWNpDI="
```

### Final Configuration

A final example server config file might look like:

```hcl
# From above
tls {
  defaults {
    cert_file = "vm-dc-server-consul-0.pem"
    key_file = "vm-dc-server-consul-0-key.pem"
    ca_file = "consul-agent-ca.pem"
  }

  internal_rpc {
    verify_incoming = true
    verify_outgoing = true
    verify_server_hostname = true
  }
}
primary_gateways = ["1.2.3.4:443"]
acl {
  enabled = true
  default_policy = "deny"
  down_policy = "extend-cache"
  tokens {
    agent = "e7924dd1-dc3f-f644-da54-81a73ba0a178"
    replication = "e7924dd1-dc3f-f644-da54-81a73ba0a178"
  }
}
encrypt = "uF+GsbI66cuWU21kiXLze5JLEX5j4iDFlDTb0ZWNpDI="

# Other server settings
server = true
datacenter = "vm-dc"
data_dir = "/opt/consul"
enable_central_service_config = true
primary_datacenter = "dc1"
connect {
  enabled = true
  enable_mesh_gateway_wan_federation = true
}
ports {
  https = 8501
  http = -1
  grpc = 8502
}
```

## Kubernetes as the Secondary

If you're running your primary datacenter on VMs then you'll need to manually
construct the [Federation Secret](/docs/k8s/installation/multi-cluster/kubernetes#federation-secret) in order to federate
Kubernetes clusters as secondaries.

-> Your VM cluster must be running mesh gateways, and have mesh gateway WAN
federation enabled. See [WAN Federation via Mesh Gateways](/docs/connect/gateways/mesh-gateway/wan-federation-via-mesh-gateways).

You'll need:

1. The root certificate authority cert placed in `consul-agent-ca.pem`.
1. The root certificate authority key placed in `consul-agent-ca-key.pem`.
1. The IP addresses of the mesh gateways running in your VM datacenter. These must
   be routable from the Kubernetes cluster.
1. If ACLs are enabled you must create an ACL replication token with the following rules:

   ```hcl
   acl = "write"
   operator = "write"
   agent_prefix "" {
     policy = "read"
   }
   node_prefix "" {
     policy = "write"
   }
   service_prefix "" {
     policy = "read"
     intentions = "read"
   }
   ```

   This token is used for ACL replication and for automatic ACL management in Kubernetes.

   If you're running Consul Enterprise you'll need the rules:

   ```hcl
   operator = "write"
   agent_prefix "" {
     policy = "read"
   }
   node_prefix "" {
     policy = "write"
   }
   namespace_prefix "" {
     acl = "write"
     service_prefix "" {
       policy = "read"
       intentions = "read"
     }
   }
   ```

1. If gossip encryption is enabled, you'll need the key.

With that data ready, you can create the Kubernetes federation secret:

```sh
kubectl create secret generic consul-federation \
    --from-literal=caCert=$(cat consul-agent-ca.pem) \
    --from-literal=caKey=$(cat consul-agent-ca-key.pem)
    # If ACLs are enabled uncomment.
    # --from-literal=replicationToken="<your acl replication token>" \
    # If using gossip encryption uncomment.
    # --from-literal=gossipEncryptionKey="<your gossip encryption key>"
```

If ACLs are enabled, you must next determine the Kubernetes API URL for the secondary cluster. The API URL of the
must be specified in the config files for all secondary clusters because secondary clusters need
to create global Consul ACL tokens (tokens that are valid in all datacenters) and these tokens can only be created
by the primary datacenter. By setting the API URL, the secondary cluster will configure a [Consul auth method](/docs/security/acl/auth-methods)
in the primary cluster so that components in the secondary cluster can use their Kubernetes ServiceAccount tokens
to retrieve global Consul ACL tokens from the primary.

To determine the Kubernetes API URL, first get the cluster name in your kubeconfig:

```shell-session
$ export CLUSTER=$(kubectl config view -o jsonpath="{.contexts[?(@.name == \"$(kubectl config current-context)\")].context.cluster}")
```

Then get the API URL:

```shell-session
$ kubectl config view -o jsonpath="{.clusters[?(@.name == \"$CLUSTER\")].cluster.server}"
https://<some-url>
```

You'll use this URL when setting `global.federation.k8sAuthMethodHost`.

Then use the following Helm config file:

```yaml
global:
  name: consul
  datacenter: dc2
  tls:
    enabled: true
    caCert:
      secretName: consul-federation
      secretKey: caCert
    caKey:
      secretName: consul-federation
      secretKey: caKey

  # Delete this acls section if ACLs are disabled.
  acls:
    manageSystemACLs: true
    replicationToken:
      secretName: consul-federation
      secretKey: replicationToken

  federation:
    enabled: true
    k8sAuthMethodHost: <kubernetes-api-url>
    primaryDatacenter: dc1

  # Delete this gossipEncryption section if gossip encryption is disabled.
  gossipEncryption:
    secretName: consul-federation
    secretKey: gossipEncryptionKey

connectInject:
  enabled: true
controller:
  enabled: true
meshGateway:
  enabled: true
server:
  extraConfig: |
    {
      "primary_gateways": ["<ip of your VM mesh gateway>", "<other ip>", ...]
    }
```

Notes:

1. You must fill out the `server.extraConfig` section with the IPs of your mesh
gateways running on VMs.
1. Set `global.federation.k8sAuthMethodHost` to the Kubernetes API URL of this cluster (including `https://`).
1. `global.federation.primaryDatacenter` should be set to the name of your primary datacenter.

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

After installation, if you're using consul-helm 0.30.0+, [create the
`ProxyDefaults` resource](/docs/k8s/installation/multi-cluster/kubernetes#proxydefaults)
to allow traffic between datacenters.

## Next Steps

In both cases (Kubernetes as primary or secondary), after installation, follow the [Verifying Federation](/docs/k8s/deployment-configurations/multi-cluster/kubernetes#verifying-federation)
section to verify that federation is working as expected.