Set maxmemory-policy=noeviction parameter for Chat Redis #1443
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In the subsequent commits I'm going to configure the parameters of Redis for Sidekiq specifically, hence updating this label to reflect purpose.
This replaces the ability to change Redis version in each environment and have different parameter groups. The motivation for this is that we want to set specific parameters to tune Redis for sidekiq and this will be coupled to the redis version. This approach is also consistent with the approach for Redis version on the shared redis instance.
This is the value that Sidekiq recommends to avoid any data being dropped if memory is exceeded. Without this configuration option Sidekiq complains: ``` WARNING: Your Redis instance will evict Sidekiq data under heavy load. The 'noeviction' maxmemory policy is recommended (current policy: 'volatile-lru'). See: https://github.com/mperham/sidekiq/wiki/Using-Redis#memory ``` To resolve this I've created a parameter group so that we can set this parameter. From googling I also understand that we need to change cluster-enabled too and then every other parameter is the same as default AWS - however I still need to confirm that.
kevindew
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Continuing my whack-a-mole process of trying to get a Terraform plan that will apply from #1443. It turns out we don't want to set cluster enabled to yes and the default option is no, so we shouldn't have been trying to change it.
kevindew
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Sep 12, 2024
Continuing my whack-a-mole process of trying to get a Terraform plan that will apply from #1443. It turns out we don't want to set cluster enabled to yes and the default option is no, so we shouldn't have been trying to change it. I've been through and compared all the other parameters and they seem to match.
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This configures the Redis instance that GOV.UK Chat uses for Sidekiq to use it's own parameter group and for that group to have
maxmemory-policy=noeviction. This is to resolve the warning we get from Sidekiq of:I need to confirm that this terraform a) actually works and b) doesn't mess up any other parameters.