I was planing to use Redis for session storage.
According to this question: What is a good session store for a single-host Node.js production app? it seems that when redis is not available 'locally' it is not fast at all.
How it looks like on heroku?
Let's assume I have my node app deployed on heroku and scaled to 4 instances:
web.1
web.2
web.3
web.4
Let's assume I provision addon redisToGo
and I use it as session store.
Redis installed locally is definitely faster, but that is not a typical use case at all. You almost always want Redis installed on a separate server, and web/app servers connect to redis over a tcp/ip connection.
That said, you usually want redis in the same data center, otherwise the latency will be too high. RedisToGo and Heroku - both work on AWS. As long as you choose the same region in both heroku and redistogo, you should be fine.
In general, Redis is good for session storage.