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Comment by systemvoltage | Hacker News Reader

Can you explain why one would use Kubernetes? I know containerization but still haven’t figured out wtf Kubernetes is. Everyone and their mother keeps telling me it’s an orchestration tool for containers. It’s as helpful as saying a Pecan pie is an orchestration of flour, sugar and pecans.

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Orchestration systems like Kubernetes, Amazon ECS, and (formerly, it’s pretty dead) Mesos run on a cluster of systems and coordinate over the network. What they’re coordinating is running your containerized services, for example your API server, micro services, etc. So you can tell the orchestration service “run 5 copies of this and listen externally on port 9000. When a request comes in on external_ip:9000, redirect it to one of the 5 service instances.” They will also restart your services if they die, keep stdout/stderr logs, and so forth. You can have very complex setups but most will never need more than what I’ve just described.

The main difference between the different orch. tools is how they pipe the data between Outside and the service cluster. Mesos didn’t help you, you had to build your own service discovery. ECS uses Amazon load balancers and some custom black-box daemons. Kubernetes famously uses a complex mesh of “ingress controllers” and kernel iptables/ipfw spoofing. All take their configurations in some form of JSON or YAML.

Thank you.

Is there some sort of a PID-feedback-loop control that monitors the CPU/memory load and helps spin up more instances if it sees more traffic? If Kubernetes doesn't do that, what piece of software can help automatically scale if there is a huge traffic spike?

Load balance AFAIK doesn't do that. It just helps distribute the load.

Using a HorizontalPodAutoscaler [1] you can scale up and down the amount of "pods" (a grouping of containers that are scheduled as a unit) based on the desired metric.

[1]: https://kubernetes.io/docs/tasks/run-application/horizontal-...

Autoscaling is a field of its own, yes. Lots of footguns, though.

Kubernetes is a multi-physical-machine operating system. In a typical OS you have CPU, RAM, etc. and the kernel decides how much of each to allocate to each running task. Kubernetes works the same way, but across multiple computers by default- and it can additionally manage any other arbitrary resource through the use of CustomResourceDefinitions (IPs, higher level concepts like “Minecraft Servers”, etc.)

If you want a (better) cooking analogy - if a container is a 'station' or a line cook in a professional kitchen, then Kubernetes is 'running the line', managing the kitchen, making sure everyone has the tools and ingredients they need.

"Orchestration" means it will manage how many of each container you have running, configuring, starting, and stopping them and possibly migrating them from one machine to another.

The term was created for virtual machines.

if you know systemd, one of its many functions is a single stop systemd controller for all of your infrastructure. Then it also gives you a single way to control storage, monitoring, load balancing and deployment from a single API.

It's neat. It is a lot of moving parts tho. I am just now trying it in a big infrastructure because we have so many bespoke parts that we have to glue together that we might as well try to use what is standard now...

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