Why would you run it in k8s as opposed to, say, ECS? Honest question here, why not run it on something simpler that requires less new concepts and achieves the same results?
k8s is nicer to use and simpler if you ignore the complex bits. Plus it's the standard.
I don't think the delta to make k8s integrated is that much work with EKS, but ability to mutate the entire infrastructe if and when you do scale wins out for me. I think the complexity, most of which you can ignore, is worth the flexibility.
Either way, since k8s landed, AWS itself has started improving too.
In ECS you have abstractions like task definitions, tasks, and services, all of which are specific to ECS, and so are new concepts for someone learning it originally. In Kubernetes a typical web app or service deployment uses a Deployment, a Service, and an Ingress. It isn't any harder to learn to use than ECS, and I find the k8s abstractions better designed anyway.
If you're already using ECS, and are happy with it, then there may be no strong reason to switch to k8s. But for anyone deciding which to use for the first time, I'd strongly advise against ECS, for several reasons.
One is that k8s has become an industry standard, and you can deploy k8s applications on many different clouds as well as non-cloud environments. As such, learning k8s is a much more transferable skill. K8s is an open source project run by the Cloud Native Computing Foundation, with many major and minor contributors. You can easily install a k8s distribution on your own machine using one of the small "edge" distributions like k3s or microk8s.
While in theory, some of the above is true for ECS, in practice it just doesn't have anything like the momentum of k8s, and afaict there aren't many people deploying ECS on other clouds or onprem.
Because of these kinds of differences, all in all I don't think there's much of a contest here. It's not so much that ECS is bad, but rather that k8s is technically excellent, and an industry standard backed by many companies, with significant momentum and an enormous ecosystem.
- Countless Helm charts
- Development tools like Telepresence
- Many GUIs / terminal UIs
- CI/CD tools like Argo
- Logging and monitoring tools
- Chaos engineering tools
- Security and compliance tools
- Service meshes / request tracing
- Operators for self-healing services
- Resource provisioning
- etc...