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Redis replication and failover providing your own instance

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

Alternatively, you may opt to manage your own Redis instance separate from the Linux package.

Requirements

The following are the requirements for providing your own Redis instance:

  • Find the minimum Redis version that is required in the requirements page.
  • Standalone Redis or Redis high availability with Sentinel are supported. Redis Cluster is not supported.
  • Managed Redis from cloud providers such as AWS ElastiCache works fine. If these services support high availability, be sure it is not the Redis Cluster type.

Note the Redis node's IP address or hostname, port, and password (if required).

Redis as a managed service in a cloud provider

  1. Set up Redis according to the requirements.

  2. Configure the GitLab application servers with the appropriate connection details for your external Redis service in your /etc/gitlab/gitlab.rb file:

    When using a single Redis instance:

    redis['enable'] = false

gitlab_rails['redis_host'] = '<redis_instance_url>'
gitlab_rails['redis_port'] = '<redis_instance_port>'

# Required if Redis authentication is configured on the Redis node
gitlab_rails['redis_password'] = '<redis_password>'

# Set to true if instance is using Redis SSL 
gitlab_rails['redis_ssl'] = true

    When using separate Redis Cache and Persistent instances:

    redis['enable'] = false

# Default Redis connection
gitlab_rails['redis_host'] = '<redis_persistent_instance_url>'
gitlab_rails['redis_port'] = '<redis_persistent_instance_port>'
gitlab_rails['redis_password'] = '<redis_persistent_password>'

# Set to true if instance is using Redis SSL
gitlab_rails['redis_ssl'] = true

# Redis Cache connection
# Replace `redis://` with `rediss://` if using SSL
gitlab_rails['redis_cache_instance'] = 'redis://:<redis_cache_password>@<redis_cache_instance_url>:<redis_cache_instance_port>'

  3. Reconfigure for the changes to take effect:

    sudo gitlab-ctl reconfigure

Setting the eviction policy

When running a single Redis instance the eviction policy should be set to noeviction.

If you are running separate Redis Cache and Persistent instances, Cache should be configured as a Least Recently Used cache (LRU) with allkeys-lru while Persistent should be set to noeviction.

Configuring this depends on the cloud provider or service, but generally the following settings and values configure a cache:

  • maxmemory-policy = allkeys-lru
  • maxmemory-samples = 5

Redis replication and failover with your own Redis servers

This is the documentation for configuring a scalable Redis setup when you have installed Redis all by yourself and not using the bundled one that comes with the Linux packages, although using the Linux packages is highly recommend as we optimize them specifically for GitLab, and we take care of upgrading Redis to the latest supported version.

Note also that you may elect to override all references to /home/git/gitlab/config/resque.yml in accordance with the advanced Redis settings outlined in Configuration Files Documentation.

We cannot stress enough the importance of reading the replication and failover documentation of the Linux package Redis HA because it provides some invaluable information to the configuration of Redis. Read it before going forward with this guide.

Before proceeding on setting up the new Redis instances, here are some requirements:

  • 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 configuration file. You can bind to all interfaces (0.0.0.0) or specify the IP of the desired interface (for example, 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 also need to define the same password for the replica password definition (masterauth) in the same instance.

In addition, read the prerequisites as described in Redis replication and failover with the Linux package.

Step 1. Configuring the primary Redis instance

Assuming that the Redis primary instance IP is 10.0.0.1:

  1. Install Redis.

  2. 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

  3. Restart the Redis service for the changes to take effect.

Step 2. Configuring the replica Redis instances

Assuming that the Redis replica instance IP is 10.0.0.2:

  1. Install Redis.

  2. 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 `replicaof` pointing to the Redis primary instance with IP and port.
replicaof 10.0.0.1 6379

  3. Restart the Redis service for the changes to take effect.

  4. Go through the steps again for all the other replica 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 primary with IP 10.0.0.1 (some settings might overlap with the primary):

  1. Install Redis Sentinel.

  2. 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 primary and replicas instances.
sentinel auth-pass gitlab-redis redis-password-goes-here

## Define with `sentinel monitor` the IP and port of the Redis
## primary 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 is 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 primary by a given Sentinel, is two
##   times the failover timeout.
##
## * The time needed for a replica replicating to a wrong primary according
##   to a Sentinel current configuration, to be forced to replicate
##   with the right primary, 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 (REPLICAOF NO ONE yet not
##   acknowledged by the promoted replica).
##
## * The maximum time a failover in progress waits for all the replicas to be
##   reconfigured as replicas of the new primary. However even after this time
##   the replicas are reconfigured by the Sentinels anyway, but not with
##   the exact parallel-syncs progression as specified.
sentinel failover_timeout 30000

  3. Restart the Redis service for the changes to take effect.

  4. 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:

  1. Edit /home/git/gitlab/config/resque.yml following the example in resque.yml.example, 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

  2. Restart GitLab for the changes to take effect.

Example of minimal configuration with 1 primary, 2 replicas 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 set up firewall rules to prevent unauthorized access from other machines, and block traffic from the outside (Internet).

For this example, Sentinel 1 is configured in the same machine as the Redis Primary, Sentinel 2 in the same machine as Replica 1, and Sentinel 3 in the same machine as Replica 2.

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

  • 10.0.0.1: Redis Primary + Sentinel 1
  • 10.0.0.2: Redis Replica 1 + Sentinel 2
  • 10.0.0.3: Redis Replica 2 + Sentinel 3
  • 10.0.0.4: GitLab application

After the initial configuration, if a failover is initiated by the Sentinel nodes, the Redis nodes are reconfigured and the Primary changes permanently (including in redis.conf) from one node to the other, until a new failover is initiated again.

The same thing happens with sentinel.conf that is overridden after the initial execution, after any new sentinel node starts watching the Primary, or a failover promotes a different Primary node.

Example configuration for Redis primary and Sentinel 1

  1. In /etc/redis/redis.conf:

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

  2. 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

  3. Restart the Redis service for the changes to take effect.

Example configuration for Redis replica 1 and Sentinel 2

  1. In /etc/redis/redis.conf:

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

  2. 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

  3. Restart the Redis service for the changes to take effect.

Example configuration for Redis replica 2 and Sentinel 3

  1. In /etc/redis/redis.conf:

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

  2. 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

  3. Restart the Redis service for the changes to take effect.

Example configuration of the GitLab application

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

    production:
  url: redis://:redis-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

  2. Restart GitLab for the changes to take effect.

Troubleshooting

See the Redis troubleshooting guide.