consul/website/content/docs/k8s/deployment-configurations/servers-outside-kubernetes.mdx

---
layout: docs
page_title: Join External Servers to Consul on Kubernetes
description: >-
  Client agents that run on Kubernetes pods can join existing clusters whose server agents run outside of k8s. Learn how to expose gossip ports and bootstrap ACLs by configuring the Helm chart.
---

# Join External Servers to Consul on Kubernetes

If you have a Consul cluster already running, you can configure your
Consul clients inside Kubernetes to join this existing cluster.

The below `values.yaml` file shows how to configure the Helm chart to install
Consul clients that will join an existing cluster.

The `global.enabled` value first disables all chart components by default
so that each component is opt-in. This allows us to _only_ setup the client
agents. We then opt-in to the client agents by setting `client.enabled` to
`true`.

Next, `client.exposeGossipPorts` can be set to `true` or `false` depending on if
you want the clients to be exposed on the Kubernetes internal node IPs (`true`) or
their pod IPs (`false`).

Finally, `client.join` is set to an array of valid
[`-retry-join` values](/docs/agent/config/cli-flags#retry-join). In the
example above, a fake [cloud auto-join](/docs/install/cloud-auto-join)
value is specified. This should be set to resolve to the proper addresses of
your existing Consul cluster.

<CodeBlockConfig filename="values.yaml">

```yaml
global:
  enabled: false

client:
  enabled: true
  # Set this to true to expose the Consul clients using the Kubernetes node
  # IPs. If false, the pod IPs must be routable from the external servers.
  exposeGossipPorts: true
  join:
    - 'provider=my-cloud config=val ...'
```

</CodeBlockConfig>

-> **Networking:** Note that for the Kubernetes nodes to join an existing
cluster, the nodes (and specifically the agent pods) must be able to connect
to all other server and client agents inside and _outside_ of Kubernetes over [LAN](/docs/install/glossary#lan-gossip).
If this isn't possible, consider running a separate Consul cluster inside Kubernetes
and federating it with your cluster outside Kubernetes.
You may also consider adopting Consul Enterprise for
[network segments](/docs/enterprise/network-segments).

## Configuring TLS with Auto-encrypt

-> **Note:** Consul on Kubernetes currently does not support external servers that require mutual authentication
for the HTTPS clients of the Consul servers, that is when servers have either
`tls.defaults.verify_incoming` or `tls.https.verify_incoming` set to `true`.
As noted in the [Security Model](/docs/security#secure-configuration),
that setting isn't strictly necessary to support Consul's threat model as it is recommended that
all requests contain a valid ACL token.

Consul's auto-encrypt feature allows clients to automatically provision their certificates by making a request to the servers at startup.
If you would like to use this feature with external Consul servers, you need to configure the Helm chart with information about the servers
so that it can retrieve the clients' CA to use for securing the rest of the cluster.
To do that, you must add the following values, in addition to the values mentioned above:

<CodeBlockConfig filename="values.yaml" highlight="2-8">

```yaml
global:
  tls:
    enabled: true
    enableAutoEncrypt: true
externalServers:
  enabled: true
  hosts:
    - 'provider=my-cloud config=val ...'
```

</CodeBlockConfig>

In most cases, `externalServers.hosts` will be the same as `client.join`, however, both keys must be set because
they are used for different purposes: one for Serf LAN and the other for HTTPS connections.
Please see the [reference documentation](/docs/k8s/helm#v-externalservers-hosts)
for more info. If your HTTPS port is different from Consul's default `8501`, you must also set
`externalServers.httpsPort`.

## Configuring ACLs

If you are running external servers with ACLs enabled, there are a couple of ways to configure the Helm chart
to help initialize ACL tokens for Consul clients and consul-k8s components for you.

### Manually Bootstrapping ACLs

If you would like to call the [ACL bootstrapping API](/api-docs/acl#bootstrap-acls) yourself or if your cluster has already been bootstrapped with ACLs,
you can provide the bootstrap token to the Helm chart. The Helm chart will then use this token to configure ACLs
for Consul clients and any consul-k8s components you are enabling.

First, create a Kubernetes secret containing your bootstrap token:

```shell
kubectl create secret generic bootstrap-token --from-literal='token=<your bootstrap token>'
```

Then provide that secret to the Helm chart:

<CodeBlockConfig filename="values.yaml" highlight="4-6">

```yaml
global:
  acls:
    manageSystemACLs: true
    bootstrapToken:
      secretName: bootstrap-token
      secretKey: token
```

</CodeBlockConfig>

The bootstrap token requires the following minimal permissions:

- `acl:write`
- `operator:write` if enabling Consul namespaces
- `agent:read` if using WAN federation over mesh gateways

Next, configure external servers. The Helm chart will use this configuration to talk to the Consul server's API
to create policies, tokens, and an auth method. If you are [enabling Consul Connect](/docs/k8s/connect),
`k8sAuthMethodHost` should be set to the address of your Kubernetes API server
so that the Consul servers can validate a Kubernetes service account token when using the [Kubernetes auth method](/docs/security/acl/auth-methods/kubernetes)
with `consul login`.

<CodeBlockConfig filename="values.yaml">

```yaml
externalServers:
  enabled: true
  hosts:
    - 'provider=my-cloud config=val ...'
  k8sAuthMethodHost: 'https://kubernetes.example.com:443'
```

</CodeBlockConfig>

Your resulting Helm configuration will end up looking similar to this:

<CodeBlockConfig filename="values.yaml">

```yaml
global:
  enabled: false
  acls:
    manageSystemACLs: true
    bootstrapToken:
      secretName: bootstrap-token
      secretKey: token
client:
  enabled: true
  # Set this to true to expose the Consul clients using the Kubernetes node
  # IPs. If false, the pod IPs must be routable from the external servers.
  exposeGossipPorts: true
  join:
    - 'provider=my-cloud config=val ...'
externalServers:
  enabled: true
  hosts:
    - 'provider=my-cloud config=val ...'
  k8sAuthMethodHost: 'https://kubernetes.example.com:443'
```

</CodeBlockConfig>

### Bootstrapping ACLs via the Helm chart

If you would like the Helm chart to call the bootstrapping API and set the server tokens for you, then the steps are similar.
The only difference is that you don't need to set the bootstrap token. The Helm chart will save the bootstrap token as a Kubernetes secret.

<CodeBlockConfig filename="values.yaml">

```yaml
global:
  enabled: false
  acls:
    manageSystemACLs: true
client:
  enabled: true
  # Set this to true to expose the Consul clients using the Kubernetes node
  # IPs. If false, the pod IPs must be routable from the external servers.
  exposeGossipPorts: true
  join:
    - 'provider=my-cloud config=val ...'
externalServers:
  enabled: true
  hosts:
    - 'provider=my-cloud config=val ...'
  k8sAuthMethodHost: 'https://kubernetes.example.com:443'
```

</CodeBlockConfig>