Comment by antoncohen | Hacker News Reader

Comment by antoncohen | Hacker News Reader

I think the core point of this article is that to run replicated DBs on Kubernetes requires deep knowledge of the DBs in question. You can't just use a StatefulSet and expect it to work well.

You need to override Kubernetes' built-in controllers to customize them to the details of the database, for example when is it safe to failover, or when is it safe to scale down. Outside of Kubernetes these decisions are made by cloud services like RDS, or manually by people with knowledge like DBAs.

To put that knowledge into Kubernetes you need Custom Resource Definitions (CRDs).

I know know if it is any good, but I just found a project called KubeDB that has CRDs for various DBs: https://kubedb.com/ and https://github.com/kubedb

I wouldn't say that you need deep knowledge at this point. However, you do need at least journeyman level knowledge. Lots of folks (including me, on Patroni) are working to make more things automatic and lower the knowledge barrier, but we're not there yet.

A big part of the obstacle is that preserving state in a distributed environment is just hard, no matter what your technology, and the failure cases are generally catastrophic (lose all data, everywhere). This is true both for the new distributed databases, and for the retrofits of the older databases. So building DBMSes which can be flawlessly deployed by junior admins on random Kubernetes clusters requires a lot of plumbing and hundreds of test cases, which are hard to construct if you don't have a $big budget for cloud time in order to test things like multi-zone netsplits and other Chaos Monkey operations.

Making distributed databases simple and reliable is a lot like writing software for airplanes, but clearly that's possible, it's just hard and will take a while.

Also, the article does show us the kind of knowledge that admins will always need to have, such as the tradeoffs between asynchronous and synchronous replication.

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