gitlab-org--gitlab-foss/doc/administration/high_availability/redis.md

# Configuring Redis for GitLab HA

You can choose to install and manage Redis yourself, or you can use the one
that comes bundled with Omnibus GitLab packages.

> **Note:** Redis does not require authentication by default. See
  [Redis Security](http://redis.io/topics/security) documentation for more
  information. We recommend using a combination of a Redis password and tight
  firewall rules to secure your Redis service.

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**Table of Contents**

- [Configure your own Redis server](#configure-your-own-redis-server)
- [Configure Redis using Omnibus](#configure-redis-using-omnibus)
- [Experimental Redis Sentinel support](#experimental-redis-sentinel-support)
- [Redis Sentinel support](#redis-sentinel-support)
  - [Prerequisites](#prerequisites)
  - [Redis setup](#redis-setup)
    - [Existing single-machine installation](#existing-single-machine-installation)
    - [Omnibus packages](#omnibus-packages)
  - [Configuring Sentinel](#configuring-sentinel)
    - [How sentinel handles a failover](#how-sentinel-handles-a-failover)
    - [Sentinel setup](#sentinel-setup)
      - [Community Edition](#community-edition)
      - [Enterprise Edition](#enterprise-edition)
  - [GitLab setup](#gitlab-setup)
- [Troubleshooting](#troubleshooting)
  - [Redis replication](#redis-replication)
  - [Sentinel](#sentinel)
    - [Omnibus GitLab](#omnibus-gitlab)

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## Configure your own Redis server

If you're hosting GitLab on a cloud provider, you can optionally use a
managed service for Redis. For example, AWS offers a managed ElastiCache service
that runs Redis.

## Configure Redis using Omnibus

If you don't want to bother setting up your own Redis server, you can use the
one bundled with Omnibus. In this case, you should disable all services except
Redis.

1. Download/install Omnibus GitLab using **steps 1 and 2** from
   [GitLab downloads](https://about.gitlab.com/downloads). Do not complete other
   steps on the download page.
1. Create/edit `/etc/gitlab/gitlab.rb` and use the following configuration.
   Be sure to change the `external_url` to match your eventual GitLab front-end
   URL:

    ```ruby
    external_url 'https://gitlab.example.com'

    # Disable all services except Redis
    redis['enable'] = true
    bootstrap['enable'] = false
    nginx['enable'] = false
    postgresql['enable'] = false
    gitlab_rails['enable'] = false

    # Redis configuration
    redis['port'] = 6379
    redis['bind'] = '0.0.0.0'
    redis['password'] = 'redis-password-goes-here'
    ```

1. Run `sudo gitlab-ctl reconfigure` to install and configure Redis.

    > **Note**: This `reconfigure` step will result in some errors.
      That's OK - don't be alarmed.

1. Run `touch /etc/gitlab/skip-auto-migrations` to prevent database migrations
   from running on upgrade. Only the primary GitLab application server should
   handle migrations.

## Experimental Redis Sentinel support

   > Experimental Redis Sentinel support was [Introduced][ce-1877] in GitLab 8.11.
     Starting with 8.14, Redis Sentinel is no longer experimental.
     If you used with versions `< 8.14` before, please check the updated
     documentation below.

## Redis Sentinel support

Since GitLab 8.11, you can configure a list of Redis Sentinel servers that
will monitor a group of Redis servers to provide you with a standard failover
support.

To get a better understanding on how to correctly setup Sentinel, please read
the [Redis Sentinel documentation](http://redis.io/topics/sentinel) first, as
failing to configure it correctly can lead to data loss.

Redis Sentinel can handle the most important tasks in a HA environment to help
keep servers online with minimal to no downtime:

- Monitors master and slave instances to see if they are available
- Promote a slave to master when the master fails.
- Demote a master to slave when failed master comes back online (to prevent
  data-partitioning).
- Can be queried by clients to always connect to the correct master server.

The configuration consists of three parts:

- Setup Redis Master and Slave nodes
- Setup Sentinel nodes
- Setup GitLab

### Prerequisites

You need at least `3` independent machines: physical, or VMs running into
distinct physical machines.

If you fail to provision the machines in that specific way, any issue with
the shared environment can bring your entire setup down.

Read carefully how to configure those components below.

### Redis setup

You must have at least `3` Redis servers: `1` Master, `2` Slaves, and they need to
be each in a independent machine (see explanation above).

They should be configured the same way and with similar server specs, as
in a failover situation, any `Slave` can be elected as the new `Master` by
the Sentinel servers.

With Sentinel, you must define a password to protect the access as both
Sentinel instances and other redis instances should be able to talk to
each other over the network.

You'll need to define both `requirepass` and `masterauth` in all
nodes. At any time during a failover the Sentinels can reconfigure a node
and change it's status from `Master` to `Slave` and vice versa.

Initial `Slave` nodes require an additional `slaveof` setting in `redis.conf`
pointing to the initial `Master`.

#### Existing single-machine installation

If you already have a single-machine GitLab install running, you will need to
replicate from this machine first, before de-activating the Redis instance
inside it.

Your single-machine install will be the initial `Master`, and the `3` others
should be configured as `Slave` pointing to this machine.

After replication catchs-up, you will need to stop services in the
single-machine install, to rotate the `Master` to one of the new nodes.

Make the required changes in configuration and restart the new nodes again.

To disable redis in the single install, edit `/etc/gitlab/gitlab.rb`:

```ruby
redis['enable'] = false
```

#### Omnibus packages

You need to install the Omnibus GitLab package in `3` independent machines.

**Configuring Master Redis instance**

You will need to configure the following:

1. Define a `redis['bind']` address pointing to a local IP that your other machines
   can reach you. If you really need to bind to an external acessible IP, make
   sure you add extra firewall rules to prevent unauthorized access.
1. Define a `redis['port']` so redis can listen for TCP requests which will
   allow other machines to connect to it.
1. Set up a password authentication with `redis['master_password']` (use the same
   password in all nodes).

In `/etc/gitlab/gitlab.rb`:

```ruby
## Redis TCP support (will disable UNIX socket transport)
redis['bind'] = '0.0.0.0' # or specify an IP to bind to a single one
redis['port'] = 6379
redis['password'] = 'redis-password-goes-here'
redis['master_password'] = 'redis-password-goes-here'
```

Reconfigure Omnibus GitLab for the changes to take effect: `sudo gitlab-ctl reconfigure`

**Configuring Slave Redis instances**

You need to make the same changes listed for the `Master` instance,
with an additional `Slave` section as in the example below:

```ruby
redis['bind'] = '0.0.0.0' # or specify an IP to bind to a single one
redis['port'] = 6379
redis['password'] = 'redis-password-goes-here'
redis['master_password'] = 'redis-password-goes-here'

## Slave redis instance
redis['master'] = false
redis['master_ip'] = '10.10.10.10' # IP of master Redis server
redis['master_port'] = 6379 # Port of master Redis server
```

Reconfigure Omnibus GitLab for the changes to take effect: `sudo gitlab-ctl reconfigure`

---

Now that the Redis servers are all set up, let's configure the Sentinel
servers.

If you are not sure if your Redis servers are working and replicating
correctly, please read the [Troubleshooting  Replication](#troubleshooting-replication)
and fix it before proceeding with Sentinel setup.

### Configuring Sentinel

You must have at least `3` Redis Sentinel servers, and they need to
be each in a independent machine. You can configure them in the same
machines where you've configured the other Redis servers.

This number is required for the consensus algorithm to be effective
in the case of a failure. **You should always have an `odd` number
of Sentinel nodes provisioned**.

#### How sentinel handles a failover

If (`quorum` value of) Sentinels  agree the fact the `master` is not reachable,
Sentinels will try to elect a temporary `Leader`. The **Majority** of the
Sentinels must agree to start a failover.

If you don't have the **Majority** of the Sentinels online (for example if you
are under a network partitioning), a failover **will not be started**.

For example, for a cluster of `3` Sentinels, at least `2` must agree on a
`Leader`. If you have total of `5` at least `3` must agree on a `Leader`.

The `quorum` is only used to detect failure, not to elect the `Leader`.

Official [Sentinel documentation](http://redis.io/topics/sentinel#example-sentinel-deployments)
also lists different network topologies and warns againts situations like
network partition and how it can affect the state of the HA solution. Make
sure you read it carefully and understand the implications in your current
setup.

GitLab Enterprise Edition provides [automated way to setup and run](#sentinel-setup-ee-only) the Sentinel daemon.

#### Sentinel setup

##### Community Edition

With GitLab Community Edition, you need to install, configure, execute and
monitor Sentinel from source. Omnibus GitLab Community Edition package does
not support Sentinel configuration.

See documentation for Source Install [here](redis_source.md).

##### Enterprise Edition

To setup sentinel, edit `/etc/gitlab/gitlab.rb` file:

```ruby

## When you install Sentinel in a separate machine, you need to control which
## other services will be running in it.
## We've simplified the choice using special "roles" settings:

## Enabled Sentinel and Redis Master services
redis_sentinel_role['enable'] = true
redis_master_role['enable'] = true

## Enabled Sentinel and Redis Slave services
redis_sentinel_role['enable'] = true
redis_slave_role['enable'] = true

## Configure Redis
redis['master_name'] = 'gitlab-redis' # must be the same in every sentinel node
redis['master_ip'] = '10.0.0.1' # ip of the initial master redis instance
redis['master_port'] = 6379 # port of the initial master redis instance
redis['master_password'] = 'redis-password-goes-here' # the same value defined in redis['password'] in the master instance

## Configure Sentinel
# sentinel['bind'] = '0.0.0.0' # bind to all interfaces, uncomment to specify an IP and bind to a single one
# sentinel['port'] = 26379 # uncomment to change default port

## Quorum must reflect the amount of voting sentinels it take to start a failover.
## Value must NOT be greater then the ammount of sentinels.
##
## The quorum can be used to tune Sentinel in two ways:
## 1. If a the quorum is set to a value smaller than the majority of Sentinels
##    we deploy, we are basically making Sentinel more sensible to master failures,
##    triggering a failover as soon as even just a minority of Sentinels is no longer
##    able to talk with the master.
## 1. If a quorum is set to a value greater than the majority of Sentinels, we are
##    making Sentinel able to failover only when there are a very large number (larger
##    than majority) of well connected Sentinels which agree about the master being down.s
sentinel['quorum'] = 2

## Consider unresponsive server down after x amount of ms.
# sentinel['down_after_milliseconds'] = 10000

## Specifies the failover timeout in milliseconds. It is used in many ways:
##
## - The time needed to re-start a failover after a previous failover was
##   already tried against the same master by a given Sentinel, is two
##   times the failover timeout.
##
## - The time needed for a slave replicating to a wrong master according
##   to a Sentinel current configuration, to be forced to replicate
##   with the right master, is exactly the failover timeout (counting since
##   the moment a Sentinel detected the misconfiguration).
##
## - The time needed to cancel a failover that is already in progress but
##   did not produced any configuration change (SLAVEOF NO ONE yet not
##   acknowledged by the promoted slave).
##
## - The maximum time a failover in progress waits for all the slaves to be
##   reconfigured as slaves of the new master. However even after this time
##   the slaves will be reconfigured by the Sentinels anyway, but not with
##   the exact parallel-syncs progression as specified.
# sentinel['failover_timeout'] = 60000
```

In the example above we've used `redis_sentinel_role` and `redis_master_role`
which simplify the ammount of configuration changes.

If you want more control, here is what each one sets for you automatically
when enabled:

```ruby
## Redis Sentinel Role
redis_sentinel_role['enable'] = true

# When Sentinel Role is enabled, the following services are enabled/disabled:
sentinel['enable'] = true

# This others are disabled:
redis['enable'] = false
bootstrap['enable'] = false
nginx['enable'] = false
postgresql['enable'] = false
gitlab_rails['enable'] = false
mailroom['enable'] = false

## Redis master/slave Role:
redis_master_role['enable'] = true # enable only one of them
redis_slave_role['enable'] = true # enable only one of them

# When Redis Master or Slave role are enabled, the following services are enabled/disabled:
# (Note that if redis and sentinel roles are combined both services will be enabled)

# When Sentinel Role is enabled, the following services are enabled/disabled:
redis['enable'] = true

# This others are disabled:
sentinel['enable'] = false
bootstrap['enable'] = false
nginx['enable'] = false
postgresql['enable'] = false
gitlab_rails['enable'] = false
mailroom['enable'] = false

# Redis Slave role also change this setting from default 'true' to 'false':
redis['master'] = false
```
---

The final part is to inform the main GitLab application server of the Redis
master and the new sentinels servers.

### GitLab setup

You can enable or disable Sentinel support at any time in new or existing
installations. From the GitLab application perspective, all it requires is
the correct credentials for the Sentinel nodes.

While it doesn't require a list of all Sentinel nodes, in case of a failure,
it needs to access at one of listed ones.

>**Note:**
The following steps should be performed in the [GitLab application server](gitlab.md)
which ideally should not have Redis or Sentinels in the same machine for a HA setup.

1. Edit `/etc/gitlab/gitlab.rb` and add/change the following lines:

    ```ruby
    redis['master_name'] = "gitlab-redis"
    redis['master_password'] = 'redis-password-goes-here'
    gitlab_rails['redis_sentinels'] = [
      {'host' => '10.10.10.1', 'port' => 26379},
      {'host' => '10.10.10.2', 'port' => 26379},
      {'host' => '10.10.10.3', 'port' => 26379}
    ]
    ```

1. [Reconfigure] GitLab for the changes to take effect.

## Troubleshooting

There are a lot of moving parts that needs to be taken care carefully
in order for the HA setup to work as expected.

Before proceeding with the troubleshooting below, check your firewall
rules:
- Redis machines
   - Accept TCP connection in `6379`
   - Connect to the other Redis machines via TCP in `6379`
- Sentinel machines
   - Accept TCP connection in `26379`
   - Connect to other Sentinel machines via TCP in `26379`
   - Connect to the Redis machines via TCP in `6379`

### Redis replication

You can check if everything is correct by connecting to each server using
`redis-cli` application, and sending the `INFO` command.

If authentication was correctly defined, it should fail with:
`NOAUTH Authentication required` error. Try to authenticate with the
previous defined password with `AUTH redis-password-goes-here` and
try the `INFO` command again.

Look for the `# Replication` section where you should see some important
information like the `role` of the server.

When connected to a `master` redis, you will see the number of connected
`slaves`, and a list of each with connection details:

```
# Replication
role:master
connected_slaves:1
slave0:ip=10.133.5.21,port=6379,state=online,offset=208037514,lag=1
master_repl_offset:208037658
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:206989083
repl_backlog_histlen:1048576
```

When it's a `slave`, you will see details of the master connection and if
its `up` or `down`:

```
# Replication
role:slave
master_host:10.133.1.58
master_port:6379
master_link_status:up
master_last_io_seconds_ago:1
master_sync_in_progress:0
slave_repl_offset:208096498
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
```

### Sentinel

#### Omnibus GitLab

If you get an error like: `Redis::CannotConnectError: No sentinels available.`,
there may be something wrong with your configuration files or it can be related
to [this issue][gh-531].

You must make sure you are defining the same value in `redis['master_name']`
and `redis['master_pasword']` as you defined for your sentinel node.

The way the redis connector `redis-rb` works with sentinel is a bit
non-intuitive. We try to hide the complexity in omnibus, but it still requires
a few extra configs.

---

To make sure your configuration is correct:

1. SSH into your GitLab application server
1. Enter the Rails console:

    ```
    # For Omnibus installations
    sudo gitlab-rails console

    # For source installations
    sudo -u git rails console production
    ```

1. Run in the console:

    ```ruby
    redis = Redis.new(Gitlab::Redis.params)
    redis.info
    ```

    Keep this screen open and try to simulate a failover below.

1. To simulate a failover on master Redis, SSH into the Redis server and run:

    ```bash
    # port must match your master redis port, and the sleep time must be a few seconds bigger than defined one
     redis-cli -h localhost -p 6379 DEBUG sleep 20
    ```

1. Then back in the Rails console from the first step, run:

    ```
    redis.info
    ```

    You should see a different port after a few seconds delay
    (the failover/reconnect time).

---

Read more on high-availability configuration:

1. [Configure the database](database.md)
1. [Configure NFS](nfs.md)
1. [Configure the GitLab application servers](gitlab.md)
1. [Configure the load balancers](load_balancer.md)

[ce-1877]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/1877
[restart]: ../restart_gitlab.md#installations-from-source
[reconfigure]: ../restart_gitlab.md#omnibus-gitlab-reconfigure
[gh-531]: https://github.com/redis/redis-rb/issues/531
[gh-534]: https://github.com/redis/redis-rb/issues/534