consul/website/content/docs/k8s/operations/tls-on-existing-cluster.mdx

---
layout: docs
page_title: Configure TLS on an Existing Cluster
description: Configure TLS on an existing Consul cluster running in Kubernetes
---

# Configuring TLS on an Existing Cluster

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 Connect

If you're **not using Consul Connect**, 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 will trigger a rolling update of the clients, as well as any
other `consul-k8s` components, such as sync catalog or client snapshot deployments.

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

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`
   to ensure Kubernetes doesn't schedule any new workloads on those nodes
   and instead schedules onto the new nodes, which shortly will be TLS-enabled.

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](/docs/k8s/upgrade#upgrading-consul-servers)
   and `client.updateStrategy` to `OnDelete` to manually trigger an upgrade of the clients.

1. Run `helm upgrade` with the above config file. The upgrade will trigger an update of all
   components except clients and servers, such as the Consul Connect webhook deployment
   or the sync catalog deployment. Note that the sync catalog and the client
   snapshot deployments will not be in the `ready` state until the clients on their
   nodes are upgraded. It is OK to proceed to the next step without them being ready
   because Kubernetes will keep the old deployment pod around, and so there will be no
   downtime.

1. Gradually perform an upgrade of the clients by deleting client pods on the **new** node
   pool.

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

1. Redeploy all your Connect-enabled applications.
   One way to trigger a redeploy is to run `kubectl drain` on the nodes in the old pool.
   Now that the Connect webhook is TLS-aware, it will add 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](/docs/k8s/upgrade#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.