Allow REDIS_CLUSTER environment variable to use Redis in cluster mode

[n1mmy]

Using a Redis cluster instead of a single host allows for a more high-availability deployment.

This patch is only allows a single seed host. A more full implementation would have some way to support multiple seed hosts (eg a comma separated list, or multiple environment variables). However, this is enough to get started and works well in environments that have a single name/IP that will connect to a redis cluster (eg a load balancer or a kubernetes service).

[J0WI]

There are several similar PRs: #2334, #2288 and #2236
Would you like to integrate them here?

[n1mmy]

@J0WI I can give it shot when I have some free development time in the next week or two. I don't have a great testing environment at the moment, but I'll figure something out.

Please don't wait for me though, if other things are ready to merge go ahead and merge them and I can update this PR for the new changes.

[n1mmy]

After looking at the other PRs in more detail, I realize this PR needs to update redis.config.php as well. I will update it when I am able. Please do not merge yet.

[n1mmy]

Nevermind. I found a better way to accomplish what I was trying to do without having to change the docker image.

In case anyone is looking for how to set up redis cluster mode, here's what I did:

1. For your first run of the container to set up the config file, use the REDIS_HOST environment variable to get a starter redis config. For all subsequent runs, do not set REDIS_HOST so it does not create an incorrect session.ini file.

2. Manually edit config/config.php and replace the redis section with redis.cluster section. For example:

  'redis.cluster' =>
  array (
    'seeds' =>
    array (
      0 => '10.103.186.138:6379',
    ),
    'password' => '',
    'port' => 6379,
    'dbindex' => 0,
    'timeout' => 1.5,
    'failover_mode' => 2,
  ),

3. Bind mount a single .ini file into /usr/local/etc/php/conf.d. Do not bind mount a whole directory here, it would overshadow important files.

Here are the contents of my custom-session.ini file:

session.save_handler = rediscluster
session.save_path = "seed[]=10.103.186.138:6379"
redis.session.locking_enabled = 1
redis.session.lock_retries = -1
redis.session.lock_wait_time = 10000

If you are running docker on the command line, you can bind mount it into the appropriate place by adding -v ./custom-session.ini:/usr/local/etc/php/conf.d/custom-session.ini

If you are using Kubernetes, you can use a ConfigMap and a volumeMount with subPath to accomplish this. Here are some snippets from my config.

apiVersion: v1
kind: ConfigMap
metadata:
  namespace: nextcloud
  name: nextcloud-config
data:
  custom-session.ini: |-
    session.save_handler = rediscluster
    session.save_path = "seed[]=10.103.186.138:6379"
    redis.session.locking_enabled = 1
    redis.session.lock_retries = -1
    redis.session.lock_wait_time = 10000

---

apiVersion: apps/v1
kind: Deployment
...
      volumes:
      - name: html
        persistentVolumeClaim:
          claimName: nextcloud-data-pvc
          readOnly: false
      - name: nextcloud-config
        configMap:
          name: nextcloud-config
...
        volumeMounts:
        - mountPath: /var/www/html
          name: html
        - mountPath: /usr/local/etc/php/conf.d/custom-session.ini
          name: nextcloud-config
          subPath: custom-session.ini

Once you php sessions using redis cluster and nextcloud itself using redis cluster, you can scale to multiple replicas of the nextcloud process and have a high availability setup.

Hope this helps someone in the future!