Skip to content

Redis#

Lagoon Redis image Dockerfile, based on official redis:alpine image.

This Dockerfile is intended to be used to set up a standalone Redis ephemeral server by default.

Supported versions#

  • 5 (available for compatibility only, no longer officially supported) - uselagoon/redis-5 or uselagoon/redis-5-persistent
  • 6 Dockerfile - uselagoon/redis-6 or uselagoon/redis-6-persistent
  • 7 Dockerfile - uselagoon/redis-7 or uselagoon/redis-7-persistent

Usage#

There are 2 different flavors of Redis Images: Ephemeral and Persistent.

Ephemeral#

The ephemeral image is intended to be used as an in-memory cache for applications and will not retain data across container restarts.

When being used as an in-memory (RAM) cache, the first thing you might want to tune if you have large caches is to adapt the MAXMEMORY variable. This variable controls the maximum amount of memory (RAM) which redis will use to store cached items.

Persistent#

The persistent Redis image will persist data across container restarts and can be used for queues or application data that will need persistence.

We don't typically suggest using a persistent Redis for in-memory cache scenarios as this might have unintended side-effects on your application while a Redis container is restarting and loading data from disk.

Lagoon adaptions#

This image is prepared to be used on Lagoon. There are therefore some things already done:

  • Folder permissions are automatically adapted with fix-permissionsso this image will work with a random user.
  • The files within /etc/redis/* are templated using envplate via a container-entrypoint.

Included redis.conf configuration file#

The image ships a default Redis configuration file, optimized to work on Lagoon.

Environment Variables#

Some options are configurable via environment variables.

Environment Variable Default Description
DATABASES -1 Default number of databases created at startup.
LOGLEVEL notice Define the level of logs.
MAXMEMORY 100mb Maximum amount of memory.
MAXMEMORYPOLICY allkeys-lru The policy to use when evicting keys if Redis reaches its maximum memory usage.
REDIS_PASSWORD disabled Enables authentication feature.

Custom configuration#

By building on the base image you can include custom configuration. See https://github.com/redis/redis/blob/7.2.5/redis.conf for full documentation of the Redis configuration file.

Redis-persistent#

Based on the Lagoon redis image, the Lagoon redis-persistent Docker image is intended for use when the Redis service must be utilized in persistent mode (ie. with a persistent volume where keys will be saved to disk).

It differs from redis only with the FLAVOR environment variable, which will use the respective Redis configuration according to the version of redis in use.

Troubleshooting#

The Lagoon Redis images all come pre-loaded with the redis-cli command, which allows for querying the Redis service for information and setting config values dynamically. To use this utility, you can simply SSH into your Redis pod by using the instructions here with redis as the pod value then run it from the terminal once you've connected.

Maximum Memory Policy#

By default, the Lagoon redis images are set to use the allkeys-lru policy. This policy will alow ANY keys stored in Redis to be evicted if/when the Redis service hits its maxmemory limit according to when the key was least recently used.

For typical installations, this is the ideal configuration, as Drupal may not set a TTL value for each key cached in Redis. If the maxmemory-policy is set to something like volatile-lru and Drupal doesn't provide these TTL tags, this would result in the Redis container filling up, being totally unable to evict ANY keys, and ceasing to accept new cache keys at all.

More information on Redis' maxmemory policies can be found in Redis' official documentation.

Proceed with Caution

Changing this setting can lead to Redis becoming completely full and cause outages as a result.

Tuning Redis' maxmemory value#

Finding the optimal amount of memory to give Redis can be quite the difficult task. Before attempting to tune your Redis cache's memory size, it is prudent to let it run normally for as long as practical, with at least a day of typical usage being the ideal minimum timeframe.

There are a few high level things you can look at when tuning these memory values:

  • The first thing to check is the percentage of memory in use by Redis currently.
    • If this percentage is less than 50%, you might consider lowering the maxmemory value by 25%.
    • If this percentage is between 50% and 75%, things are running just fine.
    • If this value is greater than 75%, then it's worth looking at other variables to see if maxmemory needs to be increased.
  • If you find that your Redis' memory usage percentage is high, the next thing to look at is the number of key evictions.
    • A large number of key evictions and a memory usage greater than 95% is a fairly good indicator that your redis needs a higher maxmemory setting.
    • If the number of key evictions doesn't seem high and typical response times are reasonable, this is simply indicative of Redis doing its job and managing its allocated memory as expected.

Example commands#

The following commands can be used to view information about the Redis service:

  • View all info about the Redis service: redis-cli info
  • View service memory information: redis-cli info memory
  • View service keyspace information: redis-cli info keyspace
  • View service statistics: redis-cli info stats

It is also possible to set values for the Redis service dynamically without a restart of the Redis service. It is important to note that these dynamically set values will not persist if the pod is restarted (which can happen as a result of a deployment, maintenance, or even just being shuffled from one node to another).

  • Set maxmemory config value dynamically to 500mb: config set maxmemory 500mb
  • Set maxmemory-policy config value dynamically to volatile-lru: config set maxmemory-policy volatile-lru