open-consul/website/content/docs/k8s/upgrade/index.mdx

---
layout: docs
page_title: Upgrade
sidebar_title: Upgrade
description: Upgrade Consul on Kubernetes
---

# Upgrade Consul on Kubernetes

## Upgrade Types

Consul on Kubernetes will need to be upgraded/updated if you change your Helm configuration,
if a new Helm chart is released, or if you wish to upgrade your Consul version.

### Helm Configuration Changes

If you make a change to your Helm values file, you will need to perform a `helm upgrade`
for those changes to take effect.

For example, if you've installed Consul with the following:

```yaml
global:
  name: consul
connectInject:
  enabled: false
```

And you wish to set `connectInject.enabled` to `true`:

```diff
global:
  name: consul
connectInject:
-  enabled: false
+  enabled: true
```

Perform the following steps:

1. Determine your current installed chart version.

```bash
helm list -f consul
NAME  	NAMESPACE	REVISION	UPDATED        	STATUS  	CHART        	APP VERSION
consul	default  	2       	2020-09-30 ...	deployed	consul-0.24.0	1.8.2
```

In this example, version `0.24.0` (from `consul-0.24.0`) is being used.

1. Perform a `helm upgrade`:

   ```bash
   helm upgrade consul hashicorp/consul --version 0.24.0 -f /path/to/my/values.yaml
   ```

   **Before performing the upgrade, be sure you've read the other sections on this page,
   continuing at [Determining What Will Change](#determining-what-will-change).**

~> NOTE: It's important to always set the `--version` flag, because otherwise Helm
will use the most up-to-date version in its local cache, which may result in an
unintended upgrade.

### Helm Chart Version Upgrade

You may wish to upgrade your Helm chart version to take advantage of new features,
bugfixes, or because you want to upgrade your Consul version, and it requires a
certain Helm chart version.

1. Update your local Helm repository cache:

```bash
helm repo update
```

1. List all available versions:

```bash
helm search repo hashicorp/consul -l
NAME            	CHART VERSION	APP VERSION	DESCRIPTION
hashicorp/consul	0.24.1       	1.8.2      	Official HashiCorp Consul Chart
hashicorp/consul	0.24.0       	1.8.1      	Official HashiCorp Consul Chart
...
```

Here we can see that the latest version of `0.24.1`.

1. To determine which version you have installed, issue the following command:

```bash
helm list -f consul
NAME  	NAMESPACE	REVISION	UPDATED        	STATUS  	CHART        	APP VERSION
consul	default  	2       	2020-09-30 ...	deployed	consul-0.24.0	1.8.2
```

In this example, version `0.24.0` (from `consul-0.24.0`) is being used.
If you want to upgrade to the latest `0.24.1` version, use the following procedure:

1. Check the changelog for any breaking changes from that version and any versions in between: https://github.com/hashicorp/consul-helm/blob/master/CHANGELOG.md.

1. Upgrade by performing a `helm upgrade` with the `--version` flag:

```bash
helm upgrade consul hashicorp/consul --version 0.24.1 -f /path/to/my/values.yaml
```

**Before performing the upgrade, be sure you've read the other sections on this page,
continuing at [Determining What Will Change](#determining-what-will-change).**

### Consul Version Upgrade

If a new version of Consul is released, you will need to perform a Helm upgrade
to update to the new version.

1. Ensure you've read the [Upgrading Consul](/docs/upgrading) documentation.
1. Ensure you've read any [specific instructions](/docs/upgrading/upgrade-specific) for the version you're upgrading
   to and the Consul [changelog](https://github.com/hashicorp/consul/blob/master/CHANGELOG.md) for that version.
1. Read our [Compatibility Matrix](/docs/k8s/upgrade/compatibility) to ensure
   your current Helm chart version supports this Consul version. If it does not,
   you may need to also upgrade your Helm chart version at the same time.
1. Set `global.consul` in your `values.yaml` to the desired version:
   ```yaml
   global:
     image: consul:1.8.3
   ```
1. Determine your current installed chart version:

```bash
helm list -f consul
NAME  	NAMESPACE	REVISION	UPDATED        	STATUS  	CHART        	APP VERSION
consul	default  	2       	2020-09-30 ...	deployed	consul-0.24.0	1.8.2
```

In this example, version `0.24.0` (from `consul-0.24.0`) is being used.

1. Perform a `helm upgrade`:

```bash
helm upgrade consul hashicorp/consul --version 0.24.0 -f /path/to/my/values.yaml`.
```

**Before performing the upgrade, be sure you've read the other sections on this page,
continuing at [Determining What Will Change](#determining-what-will-change).**

~> NOTE: It's important to always set the `--version` flag, because otherwise Helm
will use the most up-to-date version in its local cache, which may result in an
unintended upgrade.

## Determining What Will Change

Before upgrading, it's important to understand what changes will be made to your
cluster. For example, you will need to take more care if your upgrade will result
in the Consul server statefulset being redeployed.

There is no built-in functionality in Helm that shows what a helm upgrade will
change. There is, however, a Helm plugin [helm-diff](https://github.com/databus23/helm-diff)
that can be used.

1. Install `helm-diff` with:

```bash
helm plugin install https://github.com/databus23/helm-diff
```

1. If you are updating your `values.yaml` file, do so now.
1. Take the same `helm upgrade` command you were planning to issue but perform `helm diff upgrade` instead of `helm upgrade`:

```bash
helm diff upgrade consul hashicorp/consul --version 0.24.1 -f /path/to/your/values.yaml
```

This will print out the manifests that will be updated and their diffs.

1. To see only the objects that will be updated, add `| grep "has changed"`:

```bash
helm diff upgrade consul hashicorp/consul --version 0.24.1 -f /path/to/your/values.yaml |
  grep "has changed"
```

1. Take specific note if `consul, DaemonSet` or `consul-server, StatefulSet` are listed.
   This means that your Consul client daemonset or Consul server statefulset (or both) will be redeployed.

If either is being redeployed, we will follow the same pattern for upgrades as
on other platforms: the servers will be redeployed one-by-one, and then the
clients will be redeployed in batches. Read [Upgrading Consul](/docs/upgrading) and then continue
reading below.

If neither the client daemonset nor the server statefulset is being redeployed,
then you can continue with the helm upgrade without any specific sequence to follow.

## Service Mesh

If you are using Consul's service mesh features, as opposed to the [service sync](/docs/k8s/service-sync)
functionality, you must be aware of the behavior of the service mesh during upgrades.

Consul clients operate as a daemonset across all Kubernernetes nodes. During an upgrade,
if the Consul client daemonset has changed, the client pods will need to be restarted
because their spec has changed.

When a Consul client pod is restarted, it will deregister itself from Consul when it stops.
When the pod restarts, it will re-register itself with Consul.
Thus, during the period between the Consul client on a node stopping and restarting,
the following will occur:

1. The node will be deregistered from Consul. It will not show up in the Consul UI
   nor in API requests.
1. Because the node is deregistered, all service pods that were on that node will
   also be deregistered. This means they will not receive service mesh traffic
   until the Consul client pod restarts.
1. Service pods on that node can continue to make requests through the service
   mesh because each Envoy proxy maintains a cache of the locations of upstream
   services. However, if the upstream services change IPs, Envoy will not be able
   to refresh its cluster information until its local Consul client is restarted.
   So services can continue to make requests without downtime for a short period
   of time, however, it's important for the local Consul client to be restarted
   as quickly as possible.

Once the local Consul client pod restarts, each service pod needs to re-register
itself with the client. This is done automatically by the `consul-connect-lifecycle-sidecar`
sidecar container that is injected alongside each service.

Because service mesh pods are briefly deregistered during a Consul client restart,
it's **important that you do not restart all Consul clients at once**. Otherwise
you may experience downtime because no replicas of a specific service will be in the mesh.

In addition, it's **important that you have multiple replicas** for each service.
If you only have one replica, then during restart of the Consul client on the
node hosting that replica, it will be briefly deregistered from the mesh. Since
it's the only replica, other services will not be able to make calls to that
service. (NOTE: This can also be avoided by stopping that replica so it is rescheduled to
a node whose Consul client has already been updated.)

Given the above, we recommend that after Consul servers are upgraded, the Consul
client daemonset is set to use the `OnDelete` update strategy and Consul clients
are deleted one by one or in batches. See [Upgrading Consul Servers](#upgrading-consul-server)
and [Upgrading Consul Clients](#upgrading-consul-clients) for more details.

## Upgrading Consul Servers

To initiate the upgrade:

1. Change the `global.image` value to the desired Consul version
1. Set the `server.updatePartition` value _equal to the number of server replicas_.
   By default there are 3 servers, so you would set this value to `3`
1. Set the `updateStrategy` for clients to `OnDelete`

```yaml
global:
  image: 'consul:123.456'
server:
  updatePartition: 3
client:
  updateStrategy: |
    type: OnDelete
```

The `updatePartition` value controls how many instances of the server
cluster are updated. Only instances with an index _greater than_ the
`updatePartition` value are updated (zero-indexed). Therefore, by setting
it equal to replicas, none should update yet.

The `updateStrategy` controls how Kubernetes rolls out changes to the client daemonset.
By setting it to `OnDelete`, no clients will be restarted until their pods are deleted.
Without this, they would be redeployed alongside the servers because their Docker
image versions have changed. This is not desirable because we want the Consul
servers to be upgraded _before_ the clients.

1. Next, perform the upgrade:

```bash
helm upgrade consul hashicorp/consul --version <your-version> -f /path/to/your/values.yaml
```

This will not cause the servers to redeploy (although the resource will be updated). If
everything is stable, begin by decreasing the `updatePartition` value by one,
and performing `helm upgrade` again. This will cause the first Consul server
to be stopped and restarted with the new image.

1. Wait until the Consul server cluster is healthy again (30s to a few minutes).
   This can be confirmed by issuing `consul members` on one of the previous servers,
   and ensuring that all servers are listed and are `alive`.

1. Decrease `updatePartition` by one and upgrade again. Continue until
   `updatePartition` is `0`. At this point, you may remove the
   `updatePartition` configuration. Your server upgrade is complete.

## Upgrading Consul Clients

With the servers upgraded, it is time to upgrade the clients.
If you are using Consul's service mesh features, you will want to be careful
restarting the clients as outlined in [Service Mesh](#service-mesh).

You can either:

1. Manually issue `kubectl delete pod <id>` for each consul daemonset pod
2. Set the updateStrategy to rolling update with a small number:

```yaml
client:
  updateStrategy: |
    rollingUpdate:
      maxUnavailable: 2
    type: RollingUpdate
```

Then, run `helm upgrade`. This will upgrade the clients in batches, waiting
until the clients come up healthy before continuing.

3. Cordon and drain each node to ensure there are no connect pods active on it, and then delete the
   consul client pod on that node.

-> NOTE: If you are using only the Service Sync functionality, you can perform an upgrade without
following a specific sequence since that component is more resilient to brief restarts of
Consul clients.

## Configuring TLS on an Existing Cluster

If you already have a Consul cluster deployed on Kubernetes and
would like to turn on TLS for internal Consul communication,
please see
[Configuring TLS on an Existing Cluster](/docs/k8s/tls-on-existing-cluster).