How to scale an instance

If you need to scale an instance up using additional replicas, there are some things to keep in mind.

 
 Beach

Scaling configuration

Scaling an instance is in fact quite easy, you just set the desired maximum number of replicas for the instance in the Beach user interface. If you have a plan with automatic scaling support, it's three values you can set: minimum and maximum number of replicas as well as the CPU utilization that should trigger scaling.

Manual scaling information shown in the Beach UI
Automatic scaling information shown in the Beach UI

But as soon as you have more than one instance, things are different than with just one…

Cache configuration

One of those things is the Flow cache configuration. While most caches are fine with existing per replica, some should be shared between replicas:

  • Session-Caches should be shared, to avoid users losing their session should they end up on different replicas between requests.
  • The HashService has a persistent cache to store the encyption key Flow uses for some things. One of them is HMAC calculation – something that is used to secure forms and logins – and thus needs to be consistent across replicas.

We recommend putting those caches into the database – that way sessions even survive a cluster upgrade. 😎

Flow_Security_Cryptography_HashService: &pdoBackend
  backend: 'Neos\Cache\Backend\PdoBackend'
  backendOptions:
    dataSourceName: 'mysql:host=%env:BEACH_DATABASE_HOST%;dbname=%env:BEACH_DATABASE_NAME%'
    username: '%env:BEACH_DATABASE_USERNAME%'
    password: '%env:BEACH_DATABASE_PASSWORD%'
    defaultLifetime: 0

Flow_Session_Storage: *pdoBackend
Flow_Session_MetaData: *pdoBackend

Caches.yaml snippet to configure the session and hash service caches for the PDO backend.

Cover photo by Markus Spiske on Unsplash