---
layout: docs
page_title: Upgrading to Latest 1.6.x
description: >-
  Specific versions of Consul may have additional information about the upgrade
  process beyond the standard flow.
---

# Upgrading to Latest 1.6.x

## Introduction

This guide explains how to best upgrade a multi-datacenter Consul deployment that is using
a version of Consul >= 1.2.4 and < 1.6.10 while maintaining replication. If you are on a version
older than 1.2.4, please review our [Upgrading to 1.2.4](/consul/docs/upgrading/instructions/upgrade-to-1-2-x)
guide. Due to changes to the ACL system, an ACL token migration will need to be performed
as part of this upgrade. The 1.6.x series is the last series that had support for legacy
ACL tokens, so this migration _must_ happen before upgrading past the 1.6.x release series.
Here is some documentation that may prove useful for reference during this upgrade process:

- [Upgrading Legacy ACL tokens](/consul/tutorials/security-operations/access-control-token-migration) - You can find
  information about upgrading legacy ACL tokens and differences between modes here.
- [Configuration](/consul/docs/agent/config) - You can find more details
  around legacy ACL and new ACL configuration options here. Legacy ACL config options
  will be listed as deprecates as of 1.4.0.

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 >= 1.2.4 and < 1.6.10.

## 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.
- You have not already performed the ACL token migration. If you have, please skip all related
  steps.

## Considerations

There are quite a number of changes between releases. Notable changes
are called out in our [Specific Version Details](/consul/docs/upgrading/upgrade-specific#consul-1-6-3)
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.

Two very notable items are:

- 1.6.2 introduced more strict JSON decoding. Invalid JSON that was previously ignored might result in errors now (e.g., `Connect: null` in service definitions). See [[GH#6680](https://github.com/hashicorp/consul/pull/6680)].
- 1.6.3 introduced the [http_max_conns_per_client](/consul/docs/agent/config/config-files#http_max_conns_per_client) limit. This defaults to 200. Prior to this, connections per client were unbounded. [[GH#7159](https://github.com/hashicorp/consul/issues/7159)]

## Procedure

**1.** Check the replication status of the primary datacenter (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 DC2 agents to version 1.6.10 by following our [General Upgrade Process](/consul/docs/upgrading/instructions/general-process). _**Leave all DC1 agents at 1.2.4.**_ You should start observing log messages like this after that:

```log
2020/09/08 15:51:29 [DEBUG] acl: Cannot upgrade to new ACLs, servers in acl datacenter have not upgraded - found servers: true, mode: 3
2020/09/08 15:51:32 [ERR] consul: RPC failed to server 192.168.5.2:8300 in DC "dc1": rpc error making call: rpc: can't find service ConfigEntry.ListAll
```

!> **Warning:** _It is important to upgrade your primary datacenter **last**_ (the one
specified in `acl_datacenter`). If you upgrade the primary datacenter first, it will
break replication between your other datacenters. If you upgrade your other datacenters
first, they will be in legacy mode and replication from your primary datacenter will
continue working.

**4.** Check that replication is still working in DC2.

From a Consul server in DC2:

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

Take note of the `ReplicatedIndex` value.

Create a new file containing the payload for creating a new token named `test-ui-token.json`
with the following contents:

<CodeBlockConfig filename="test-ui-token.json">

```json
{
  "Name": "UI Token",
  "Type": "client",
  "Rules": "key \"\" { policy = \"write\" } node \"\" { policy = \"read\" } service \"\" { policy = \"read\" }"
}
```

</CodeBlockConfig>

From a Consul server in DC1, create a new token using that file:

```shell-session
$ curl --request PUT --header "X-Consul-Token: $MASTER_TOKEN" --data @test-ui-token.json localhost:8500/v1/acl/create
```

From a Consul server in DC2:

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

`ReplicatedIndex` should have incremented and you should find the new token listed. If you try using CLI ACL commands you will receive this error:

```log
Failed to retrieve the token list: Unexpected response code: 500 (The ACL system is currently in legacy mode.)
```

This is because Consul in legacy mode. ACL CLI commands will not work and you have to hit the old ACL HTTP endpoints (which is why `curl` is being used above rather than the `consul` CLI client).

**5.** Upgrade DC1 agents to version 1.6.10 by following our [General Upgrade Process](/consul/docs/upgrading/instructions/general-process).

Once this is complete, you should observe a log entry like this from your server agents:

```log
2020/09/10 22:11:49 [DEBUG] acl: transitioning out of legacy ACL mode
```

**6.** 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",
  "ReplicationType": "tokens",
  "ReplicatedIndex": 259,
  "ReplicatedRoleIndex": 1,
  "ReplicatedTokenIndex": 260,
  "LastSuccess": "2020-09-10T22:11:51Z",
  "LastError": "2020-09-10T22:11:43Z"
}
```

**6.** Migrate your legacy ACL tokens to the new ACL system.

~> This step _must_ be completed before upgrading to a version higher than 1.6.x.

## Post-Upgrade Configuration Changes

When moving from a pre-1.4.0 version of Consul, you will find that several of the ACL-related
configuration options were renamed. Backwards compatibility is maintained in the 1.6.x release
series, so you are old config options will continue working after upgrading, but you will want to
update those now to avoid issues when moving to newer versions.

These are the changes you will need to make:

- `acl_datacenter` is now named `primary_datacenter` (review our [docs](/consul/docs/agent/config/config-files#primary_datacenter) for more info)
- `acl_default_policy`, `acl_down_policy`, `acl_ttl`, `acl_*_token` and `enable_acl_replication` options are now specified like this (review our [docs](/consul/docs/agent/config/config-files#acl) for more info):
  ```hcl
  acl {
    enabled                  = true/false
    default_policy           = "..."
    down_policy              = "..."
    policy_ttl               = "..."
    role_ttl                 = "..."
    enable_token_replication = true/false
    enable_token_persistence = true/false
    tokens {
      master       = "..."
      agent        = "..."
      agent_master = "..."
      replication  = "..."
      default      = "..."
    }
  }
  ```

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.
