---
layout: docs
page_title: Configure TLS on an existing cluster on Kubernetes
description: >-
  Consul Helm chart 0.16.0 and later supports TLS communication within clusters. Follow the instructions to trigger rolling updates for consul-k8s without causing downtime.
---

# Configure TLS on an existing cluster on Kubernetes

As of Consul Helm version `0.16.0`, the chart supports TLS for communication
within the cluster. If you already have a Consul cluster deployed on Kubernetes,
you may want to configure TLS in a way that minimizes downtime to your applications.
Consul already supports rolling out TLS on an existing cluster without downtime.
However, depending on your Kubernetes use case, your upgrade procedure may be different.

## Gradual TLS Rollout without Consul Service Mesh

If you do not use a service mesh, follow this process.

1. Run a Helm upgrade with the following config:

   ```yaml
   global:
     tls:
       enabled: true
       # This configuration sets `verify_outgoing`, `verify_server_hostname`,
       # and `verify_incoming` to `false` on servers and clients,
       # which allows TLS-disabled nodes to join the cluster.
       verify: false
   server:
     updatePartition: <number_of_server_replicas>
   ```

  This upgrade trigger a rolling update of `consul-k8s` components.

1. Perform a rolling upgrade of the servers, as described in
   [Upgrade Consul Servers](/consul/docs/upgrade/k8s#upgrading-consul-servers).

1. Repeat steps 1 and 2, turning on TLS verification by setting `global.tls.verify`
   to `true`.

## Gradual TLS Rollout with Consul Service Mesh

Because the sidecar Envoy proxies need to talk to the Consul client agent regularly
for service discovery, we can't enable TLS on the clients without also re-injecting a
TLS-enabled proxy into the application pods. To perform TLS rollout with minimal
downtime, we recommend instead to add a new Kubernetes node pool and migrate your
applications to it.

1. Add a new identical node pool.

1. Cordon all nodes in the old pool by running `kubectl cordon`.
   This command ensures Kubernetes does not schedule any new workloads on those nodes,
   and instead schedules onto the new TLS-enabled nodes.

1. Create the following Helm config file for the upgrade:

   ```yaml
   global:
     tls:
       enabled: true
       # This configuration sets `verify_outgoing`, `verify_server_hostname`,
       # and `verify_incoming` to `false` on servers and clients,
       # which allows TLS-disabled nodes to join the cluster.
       verify: false
   server:
     updatePartition: <number_of_server_replicas>
   client:
     updateStrategy: |
       type: OnDelete
   ```

   In this configuration, we're setting `server.updatePartition` to the number of
   server replicas as described in [Upgrade Consul Servers](/consul/docs/upgrade/k8s#upgrading-consul-servers).

1. Run `helm upgrade` with the above config file.

1. At this point, all components (e.g., Consul service mesh webhook and sync catalog) should be running
   on the new node pool.

1. Redeploy all your mesh-enabled applications.
   One way to trigger a redeploy is to run `kubectl drain` on the nodes in the old pool.
   Now that the service mesh webhook is TLS-aware, it adds TLS configuration to
   the sidecar proxy. Also, Kubernetes should schedule these applications on the new node pool.

1. Perform a rolling upgrade of the servers described in
   [Upgrade Consul Servers](/consul/docs/upgrade/k8s#upgrading-consul-servers).

1. If everything is healthy, delete the old node pool.

1. Finally, set `global.tls.verify` to `true` in your Helm config file, remove the
   `client.updateStrategy` property, and perform a rolling upgrade of the servers.

-> **Note:** It is possible to do this upgrade without fully duplicating the node pool.
You could drain a subset of the Kubernetes nodes within your existing node pool and treat it
as your "new node pool." Then follow the above instructions. Repeat this process for the rest
of the nodes in the node pool.
