The Kubernetes Cloud Mainframe
I made a tongue-in-cheek comment on twitter a while back that, k8s is just the contemporary API for mainframe computing., but as someone who is both very skeptical and very excited about the possibilities of kube, this feels like something I want to expand upon.
A lot of my day-to-day work has some theoretical overlap with kube, including batch processing, service orchestration, and cloud resource allocation. Lots of people I encounter are also really excited by kube, and its interesting to balance that excitement with my understanding of the system, and to watch how Kubernetes(as a platform) impacts the way that we develop applications.
I also want to be clear that my comparison to mainframes is not a disparagement, not only do I think there's a lot of benefit to gain by thinking about the historic precedents of our paradigm. I would also assert that the trends in infrastructure over the last 10 or 15 years (e.g. virtualization, containers, cloud platforms) have focused on bringing mainframe paradigms to a commodity environment.
- clusters are static ususally functionally. I know that the public clouds have autoscaling abilities, but having really elastic infrastructure requires substantial additional work, and there are some reasonable upper-limits in terms of numbers of nodes, which makes it hard to actually operate elastically. It's probably also the case that elastic infrastructure has always been (mostly) a pipe dream at most organizations.
- some things remain quite hard, chiefly in my mind:
- autoscaling, both of the cluster itself and of the components running within the cluster. Usage patterns are don't always follow easy to detect patterns, so figuring out ways to make infrastructure elastic may take a while to converse or become common. Indeed, VMs and clouds were originally thought to be able to provide some kind of elastic/autoscaling capability, and by and large, most cloud deployments do not autoscale.
- multi-tenancy, where multiple different kinds of workloads and use-cases run on the same cluster, is very difficult to schedule for reliably or predictably, which leads to a need to overprovision more for mixed workloads.
- kubernettes does not eliminate the need for an operations team or vendor support for infrastructure or platforms.
- decentralization has costs, and putting all of the cluster configuration in etcd imposes some limitations, mostly around performance. While I think decentralization is correct, in many ways for Kubernetes, applications developers may need systems that have lower latency and tighter scheduling abilities.
- The fact that you can add applications to an existing cluster, or host a collection of small applications is mostly a symptom of clusters being over provisioned. This probably isn't bad, and it's almost certainly the case that you can reduce the overprovisioning bias with kube, to some degree.
Impact and Predictions
- applications developed for kubernettes will eventually become difficult or impossible to imagine or run without kubernettes. This has huge impacts on developer experience and test experience. I'm not sure that this is a problem, but I think it's a hell of a dependency to pick up. This was true of applications that target mainframes as well.
- Kubernetes will eventually replace vendor specific APIs for cloud infrastructure for most higher level use cases.
- Kubernetes will primarily be deployed by Cloud providers (RedHat/IBM, Google, AWS, Azure, etc.) rather than by infrastructure teams.
- Right now, vendors are figuring out what kinds of additional services users
and applications need to run in Kubernetes, but eventually there will be
another layer of tooling on top of Kubernetes:
- logging and metrics collection.
- deployment operations and configuration, particularly around coordinating dependencies.
- authentication and credential management.
- low-latency offline task orchestration.
- At some point, we'll see a move multi-cluster orchestration, or more powerful tools approach to workload isolation within a single cluster.
Kubernetes is great, and it's been cool to see how, really in the last couple of years, it's emerged to really bring together things like cloud infrastructure and container orchestration. At the same time, it (of course!) doesn't solve all of the problems that developers have with their infrastructure, and I'm really excited to see how people build upon Kubernetes to achieve some of those higher level concerns, and make it easier to build software on top of the resulting platforms.