Good article. I would add one thing to this - pick a database that scales horizontally and is distributed. CockroachDB, Elasticsearch, Mongo, Cassandra/Scylla are all good choices. If you lose one node, you don't have to be afraid of your cluster going down, meaning you can do maintenance and reconfiguration without downtime. If your load is low or bursty you can even get away with running these on some small servers such as t3 (probably minimally t3.larges). Running a cloud managed database is also a good option.
Yes, and together with that, I recommend putting all state in the distributed database (or distributed file storage for large blobs). This allows you to gracefully handle crashes, stop and restart servers, etc. because you don’t lose any state in the process.
