[smarterclayton]

As someone who designed kubernetes, I completely disagree. We designed it to run stateful workloads. From V1 we set very strong safety guarantees around how pods work and are scheduled. However, like any software infrastructure, you are vulnerable to a lot of possible failure modes. The kernel can hang on NFS mount disk operations. The SAN can go into a gray failure. A cleaning guy can pull a power cord out. Bad code in the kubelet can result in volumes failing to detach. Random people on the internet can open PRs that remove pod safety protections (happens about once every few months).

Just like any other tool that makes some things easier, Kubernetes also makes it easier to shoot yourself in the foot. Just like any solution, you have to know the system well enough to reason about it. There is still a lot that can be done to improve how we explain, document, and describe the system. But people run stateful workloads on Kube all the time, and they do it because it makes their lives easier on the balance.

[ofrzeta]

If Kubernetes was designed with stateful workloads in mind why did it take until version 1.3 to introduce petSets as an alpha feature?

[smarterclayton]

Because we prioritized stabilizing the core and having something shipped. Pod safety guarantees were part of 1.0 and ensure “at-most-one” pod with a given name at a given time on any node, which allows us to build a compute model that can be used in higher level primitives. Persistent volumes, reserving space in the DNS schema for services to have subnames, and headless services were all designed in specifically so we could do stateful sets.