alt Hacker NewsI think it's rather rare to use different services for redundancy and in most cases if you want that redundancy (e.g. to support red-black or blue-green deployments or just to support better availability via failover) I'd usually suggest using the same technology for that purpose.
I don't believe it's ever easier to manage updating two technologies than one.
I mean if I was only going to use 'one thing', it would be tech that doesn't have downtime when you replace its parts. Something like Kafka or Cassandra. Then since postgres is useful, I would likely end up adding it into the system.