---
layout: docs
page_title: Upgrading to Latest 1.2.x
description: >-
  Specific versions of Consul may have additional information about the upgrade
  process beyond the standard flow.
---

# Upgrading to Latest 1.2.x

## Introduction

This guide explains how to best upgrade a multi-datacenter Consul deployment that is using
a version of Consul >= 0.8.5 and < 1.2.4 while maintaining replication. If you are on a version
older than 0.8.5, but are in the 0.8.x series, please upgrade to 0.8.5 by following our
[General Upgrade Process](/consul/docs/upgrading/instructions/general-process). If you are on a version
older than 0.8.0, please [contact support](https://support.hashicorp.com).

In this guide, we will be using an example with two datacenters (DCs) and will be
referring to them as DC1 and DC2. DC1 will be the primary datacenter.

## Requirements

- All Consul servers should be on a version of Consul >= 0.8.5 and < 1.2.4.
- You need a Consul cluster with at least 3 nodes to perform this upgrade as documented. If
  you either have a single node cluster or several single node clusters joined via WAN, the
  servers will come up in a `No cluster leader` loop after upgrading. If that happens, you will
  need to recover the cluster using the method described [here](/consul/tutorials/datacenter-operations/recovery-outage#manual-recovery-using-peers-json).
  You can avoid this issue entirely by growing your cluster to 3 nodes prior to upgrading.

## Assumptions

This guide makes the following assumptions:

- You have at least two datacenters configured and have ACL replication enabled. If you are
  not using multiple datacenters, you can follow along and simply skip the instructions related
  to replication.

## Considerations

There are not too many major changes that might cause issues upgrading from 1.0.8, but notable changes
are called out in our [Specific Version Details](/consul/docs/upgrading/upgrade-specific#consul-1-1-0)
page. You can find more granular details in the full [changelog](https://github.com/hashicorp/consul/blob/main/CHANGELOG.md#124-november-27-2018).
Looking through these changes prior to upgrading is highly recommended.

## Procedure

**1.** Check replication status in DC1 by issuing the following curl command from a
consul server in that DC:

```shell-session
$ curl --silent --header "X-Consul-Token: $MASTER_TOKEN" localhost:8500/v1/acl/replication?pretty
```

You should receive output similar to this:

```json
{
  "Enabled": false,
  "Running": false,
  "SourceDatacenter": "",
  "ReplicatedIndex": 0,
  "LastSuccess": "0001-01-01T00:00:00Z",
  "LastError": "0001-01-01T00:00:00Z"
}
```

-> The primary datacenter (indicated by `acl_datacenter`) will always show as having replication
disabled, so this is normal even if replication is happening.

**2.** Check replication status in DC2 by issuing the following curl command from a
consul server in that DC:

```shell-session
$ curl --silent --header "X-Consul-Token: $MASTER_TOKEN" localhost:8500/v1/acl/replication?pretty
```

You should receive output similar to this:

```json
{
  "Enabled": true,
  "Running": true,
  "SourceDatacenter": "dc1",
  "ReplicatedIndex": 9,
  "LastSuccess": "2020-09-10T21:16:15Z",
  "LastError": "0001-01-01T00:00:00Z"
}
```

**3.** Upgrade the Consul agents in all DCs to version 1.2.4 by following our [General Upgrade Process](/consul/docs/upgrading/instructions/general-process).
This should be done one DC at a time, leaving the primary DC for last.

**4.** Confirm that replication is still working in DC2 by issuing the following curl command from a
consul server in that DC:

```shell-session
$ curl --silent --header "X-Consul-Token: $MASTER_TOKEN" localhost:8500/v1/acl/replication?pretty
```

You should receive output similar to this:

```json
{
  "Enabled": true,
  "Running": true,
  "SourceDatacenter": "dc1",
  "ReplicatedIndex": 9,
  "LastSuccess": "2020-09-10T21:16:15Z",
  "LastError": "0001-01-01T00:00:00Z"
}
```

## Post-Upgrade Configuration Changes

If you moved from a pre-1.0.0 version of Consul, you will find that _many_ of the configuration
options were renamed. Backwards compatibility has been maintained, so your old config options
will continue working after upgrading, but you will want to update those now to avoid issues when
moving to newer versions.

The full list of changes is available here:

- [Upgrade Specific Versions: Consul 1.0 - Deprecated Options](/consul/docs/upgrading/upgrade-specific#deprecated-options-have-been-removed)

You can make sure your config changes are valid by copying your existing configuration files,
making the changes, and then verifying them by using `consul validate $CONFIG_FILE1_PATH $CONFIG_FILE2_PATH ...`.

Once your config is passing the validation check, replace your old config files with the new ones
and slowly roll your cluster again one server at a time – leaving the leader agent for last in each
datacenter.