Configuring non-Omnibus Redis for GitLab HA

This is the documentation for configuring a Highly Available Redis setup when you have installed Redis all by yourself and not using the bundled one that comes with the Omnibus packages.

We cannot stress enough the importance of reading the Overview section of the Omnibus Redis HA as it provides some invaluable information to the configuration of Redis. Please proceed to read it before going forward with this guide.

We also highly recommend that you use the Omnibus GitLab packages, as we optimize them specifically for GitLab, and we will take care of upgrading Redis to the latest supported version.

If you're not sure whether this guide is for you, please refer to Available configuration setups in the Omnibus Redis HA documentation.

Configuring your own Redis server

This is the section where we install and setup the new Redis instances.

Prerequisites

All Redis servers in this guide must be configured to use a TCP connection instead of a socket. To configure Redis to use TCP connections you need to define both bind and port in the Redis config file. You can bind to all interfaces (0.0.0.0) or specify the IP of the desired interface (e.g., one from an internal network).
Since Redis 3.2, you must define a password to receive external connections (requirepass).
If you are using Redis with Sentinel, you will also need to define the same password for the slave password definition (masterauth) in the same instance.

In addition, read the prerequisites as described in the Omnibus Redis HA document since they provide some valuable information for the general setup.

Step 1. Configuring the master Redis instance

Assuming that the Redis master instance IP is 10.0.0.1:

Install Redis

Edit /etc/redis/redis.conf:

## Define a `bind` address pointing to a local IP that your other machines
## can reach you. If you really need to bind to an external accessible IP, make
## sure you add extra firewall rules to prevent unauthorized access:
bind 10.0.0.1

## Define a `port` to force redis to listen on TCP so other machines can
## connect to it (default port is `6379`).
port 6379

## Set up password authentication (use the same password in all nodes).
## The password should be defined equal for both `requirepass` and `masterauth`
## when setting up Redis to use with Sentinel.
requirepass redis-password-goes-here
masterauth redis-password-goes-here

Restart the Redis service for the changes to take effect.

Step 2. Configuring the slave Redis instances

Assuming that the Redis slave instance IP is 10.0.0.2:

Install Redis

Edit /etc/redis/redis.conf:

## Define a `bind` address pointing to a local IP that your other machines
## can reach you. If you really need to bind to an external accessible IP, make
## sure you add extra firewall rules to prevent unauthorized access:
bind 10.0.0.2

## Define a `port` to force redis to listen on TCP so other machines can
## connect to it (default port is `6379`).
port 6379

## Set up password authentication (use the same password in all nodes).
## The password should be defined equal for both `requirepass` and `masterauth`
## when setting up Redis to use with Sentinel.
requirepass redis-password-goes-here
masterauth redis-password-goes-here

## Define `slaveof` pointing to the Redis master instance with IP and port.
slaveof 10.0.0.1 6379

Restart the Redis service for the changes to take effect.
Go through the steps again for all the other slave nodes.

Step 3. Configuring the Redis Sentinel instances

Sentinel is a special type of Redis server. It inherits most of the basic configuration options you can define in redis.conf, with specific ones starting with sentinel prefix.

Assuming that the Redis Sentinel is installed on the same instance as Redis master with IP 10.0.0.1 (some settings might overlap with the master):

Install Redis Sentinel

Edit /etc/redis/sentinel.conf:

## Define a `bind` address pointing to a local IP that your other machines
## can reach you. If you really need to bind to an external accessible IP, make
## sure you add extra firewall rules to prevent unauthorized access:
bind 10.0.0.1

## Define a `port` to force Sentinel to listen on TCP so other machines can
## connect to it (default port is `6379`).
port 26379

## Set up password authentication (use the same password in all nodes).
## The password should be defined equal for both `requirepass` and `masterauth`
## when setting up Redis to use with Sentinel.
requirepass redis-password-goes-here
masterauth redis-password-goes-here

## Define with `sentinel auth-pass` the same shared password you have
## defined for both Redis master and slaves instances.
sentinel auth-pass gitlab-redis redis-password-goes-here

## Define with `sentinel monitor` the IP and port of the Redis
## master node, and the quorum required to start a failover.
sentinel monitor gitlab-redis 10.0.0.1 6379 2

## Define with `sentinel down-after-milliseconds` the time in `ms`
## that an unresponsive server will be considered down.
sentinel down-after-milliseconds gitlab-redis 10000

## Define a value for `sentinel failover_timeout` in `ms`. This has multiple
## meanings:
##
## * 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 30000

Restart the Redis service for the changes to take effect.
Go through the steps again for all the other Sentinel nodes.

Step 4. Configuring the GitLab application

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 least one of listed ones.

The following steps should be performed in the GitLab application server which ideally should not have Redis or Sentinels in the same machine for a HA setup:

Edit /home/git/gitlab/config/resque.yml following the example in [resque.yml.example][resque], and uncomment the Sentinel lines, pointing to the correct server credentials:

# resque.yaml
production:
  url: redis://:redi-password-goes-here@gitlab-redis/
  sentinels:
    -
      host: 10.0.0.1
      port: 26379 # point to sentinel, not to redis port
    -
      host: 10.0.0.2
      port: 26379 # point to sentinel, not to redis port
    -
      host: 10.0.0.3
      port: 26379 # point to sentinel, not to redis port

Restart GitLab for the changes to take effect.

Example of minimal configuration with 1 master, 2 slaves and 3 Sentinels

In this example we consider that all servers have an internal network interface with IPs in the 10.0.0.x range, and that they can connect to each other using these IPs.

In a real world usage, you would also setup firewall rules to prevent unauthorized access from other machines, and block traffic from the outside (Internet).

For this example, Sentinel 1 will be configured in the same machine as the Redis Master, Sentinel 2 and Sentinel 3 in the same machines as the Slave 1 and Slave 2 respectively.

Here is a list and description of each machine and the assigned IP:

10.0.0.1: Redis Master + Sentinel 1
10.0.0.2: Redis Slave 1 + Sentinel 2
10.0.0.3: Redis Slave 2 + Sentinel 3
10.0.0.4: GitLab application

Please note that after the initial configuration, if a failover is initiated by the Sentinel nodes, the Redis nodes will be reconfigured and the Master will change permanently (including in redis.conf) from one node to the other, until a new failover is initiated again.

The same thing will happen with sentinel.conf that will be overridden after the initial execution, after any new sentinel node starts watching the Master, or a failover promotes a different Master node.

Example configuration for Redis master and Sentinel 1

In /etc/redis/redis.conf:

bind 10.0.0.1
port 6379
requirepass redis-password-goes-here
masterauth redis-password-goes-here

In /etc/redis/sentinel.conf:

bind 10.0.0.1
port 26379
sentinel auth-pass gitlab-redis redis-password-goes-here
sentinel monitor gitlab-redis 10.0.0.1 6379 2
sentinel down-after-milliseconds gitlab-redis 10000
sentinel failover_timeout 30000

Restart the Redis service for the changes to take effect.

Example configuration for Redis slave 1 and Sentinel 2

In /etc/redis/redis.conf:

bind 10.0.0.2
port 6379
requirepass redis-password-goes-here
masterauth redis-password-goes-here
slaveof 10.0.0.1 6379

In /etc/redis/sentinel.conf:

bind 10.0.0.2
port 26379
sentinel auth-pass gitlab-redis redis-password-goes-here
sentinel monitor gitlab-redis 10.0.0.1 6379 2
sentinel down-after-milliseconds gitlab-redis 10000
sentinel failover_timeout 30000

Restart the Redis service for the changes to take effect.

Example configuration for Redis slave 2 and Sentinel 3

In /etc/redis/redis.conf:

bind 10.0.0.3
port 6379
requirepass redis-password-goes-here
masterauth redis-password-goes-here
slaveof 10.0.0.1 6379

In /etc/redis/sentinel.conf:

bind 10.0.0.3
port 26379
sentinel auth-pass gitlab-redis redis-password-goes-here
sentinel monitor gitlab-redis 10.0.0.1 6379 2
sentinel down-after-milliseconds gitlab-redis 10000
sentinel failover_timeout 30000

Restart the Redis service for the changes to take effect.

Example configuration of the GitLab application

Edit /home/git/gitlab/config/resque.yml:

production:
  url: redis://:redi-password-goes-here@gitlab-redis/
  sentinels:
    -
      host: 10.0.0.1
      port: 26379 # point to sentinel, not to redis port
    -
      host: 10.0.0.2
      port: 26379 # point to sentinel, not to redis port
    -
      host: 10.0.0.3
      port: 26379 # point to sentinel, not to redis port

Restart GitLab for the changes to take effect.

Troubleshooting

We have a more detailed Troubleshooting explained in the documentation for Omnibus GitLab installations. Here we will list only the things that are specific to a source installation.

If you get an error in GitLab like Redis::CannotConnectError: No sentinels available., there may be something wrong with your configuration files or it can be related to this upstream issue.

You must make sure that resque.yml and sentinel.conf are configured correctly, otherwise redis-rb will not work properly.

The master-group-name ('gitlab-redis') defined in (sentinel.conf) must be used as the hostname in GitLab (resque.yml):

# sentinel.conf:
sentinel monitor gitlab-redis 10.0.0.1 6379 2
sentinel down-after-milliseconds gitlab-redis 10000
sentinel config-epoch gitlab-redis 0
sentinel leader-epoch gitlab-redis 0

# resque.yaml
production:
  url: redis://:myredispassword@gitlab-redis/
  sentinels:
    -
      host: 10.0.0.1
      port: 26379 # point to sentinel, not to redis port
    -
      host: 10.0.0.2
      port: 26379 # point to sentinel, not to redis port
    -
      host: 10.0.0.3
      port: 26379 # point to sentinel, not to redis port

When in doubt, please read Redis Sentinel documentation.