I covered it here: More details on how the Redis cache is utilized? - #2 by Falco
Redis is used for:
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cache
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background job queue
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persistent connections backlog and pub/sub
I’d go with a hosted service in GCP if I were in your shoes, provided they ship a recent enough version of Redis and don’t lag much behind. AWS does great in keeping up with new versions, while GCP / Azure can lag sometimes.