It seems that a proper Kubernetes setup is the modern day equivalent to the proper email server setup of the 90's or the 00's :)
Usually in my day job I have to work with these tools, and currently have a stack of 5, that mostly have incomplete documentation, zero explanation of how they actually solve the problem and nearly zero ability to debug (e.g. what value have kubernetes logs and events. Usually when you have a problem is when you have no kubernetes logs yet/anymore and the events only tell you what you already know). Now I'll probably need to learn another one, considering these three options for storage.
At the weekend, where I'm mostly trying to relax and have physically only 2/7th of the time to alot I learn the basics behind containerization, e.g. namespaces, cgroups, virtual network adapters, iptables. And I feel in this small time slot I make a lot more progress at getting to that end-to-end solution that people actually need.
The example I'm using is wordpress+mysql. It's a simple thing that covers >70% of what anybody wants to deploy. And on-premise with kubernetes+docker it's still not possible without hacks (e.g. for volumeclaims and logging), after, I don't know, 4 years of Kubernetes? I bet in spending 2 years worth of weekends any normal person can come up with something better.
---
Re missing features, examples for Kubernetes:
A) Why does Kubernetes not solve the networking part? If I have a cluster and containers that may run in different places, of course the tooling I use to maintain that cluster needs to ensure that containers can talk to each other. There can be an abstract API and the option for other people to write plugins, but the core needs to come with one solution, that mostly works and is debuggable when not.
B) CrashLoopBackoff. Why did no Kubernetes developer get the idea that this state may require any kind of log/debugging?
C) Why does kubernetes assign random ports to services and not provide a simple way to retrieve them? Of course I can get them after I've learned the JSON api. But usually that is not considered a solution but hacking. I really don't care what the service is running on, I just want to use it.
D) Why do I need to manually say how many containers should run for each service? There are very distinct options a user may need. E.g., most services should run 1 instance and replace it if it dies. If it needs reliability I want to define how reliable it should be and accordingly the cluster should decide if it needs 2, 3 or 5 instances. And lastly I want to run stuff on all my nodes. Each node with a container. That is not even possible afaik.
E) Most kubernetes tools are not working well with environment proxies. For instance kube-proxy shell tool will completely bug out. But surprise, clusters make a lot of sense in enterprise environments, and enterprise environments have proxies. It's also not a hard setup for testing. A raspberry pie can be your home networks proxy.
F) on premise storage solutions, considering that a restarted container may not run on the same host.
G) Since not much is really running right now we didn't run into that problem yet. But it's totally possible that the whole cluster runs out of resources. I haven't seen any piece of info about the general cluster status and when I need to increase or replace infrastructure.
Honestly if I don't have all these things solved, am I really better of using Kubernetes or writing my own scripts? I think it currently is about equal in effort. And if that's the case my own solution has the huge advantage of being under my control and allowing me to learn a lot of new things.
How are you setting up your cluster?
A) Kubernetes abstracts the networks solution so people can choose between multiple implementations. Some people already use openstack and want to use their openvswitch network for their containers others want to use a pure container network like flannel. Kubernetes distributions usually come with a integrated network solution.
B) You can still retrieve the logs from a container is CrashLoopBackOffState. You can even retrieve the logs from the previously failed container by using the `kubectl logs <container> --previous`. Applications can write information about their failure to /dev/termination-log which can be used to debug the failure.
C) You can define the port yourself otherwise kubernetes defaults to a random port to avoid port conflicts. The recommended way to expose HTTP services would be by using ingress.
D) You can run an instance on every node by using a daemonset.
E) Are you talking about outbound traffic from your containers to an external system? You would need to configure this in the container engine and the container itself. I had little problem doing this in an enterprise environment that required an http proxy for all external communication.
F) You can attach you existing SAN solution over iSCSI, fibre channel or even NFS. Another solution would be to run a distribution storage like ceph or glusterfs in kubernetes for kubernetes. You then provision persistent volumes that are attached to the node your pod is running on. If your pod is rescheduled the volume will be moved too.
G) If you have resource requests/limits set kubernetes will not schedule your pods if you have no resources available.
Re proxy: Not only that, but also. Let's say you have single instance deployment, and run kube-dashboard. You want to access the dashboard on localhost:8080 so you start the kube-proxy shell command. What actually happens is that the go code underneath kube-proxy will redirect the request through your $http_proxy, even if localhost, the dashboard's internal address, and your hosts external address are in the $no_proxy environment. And if your network proxy doesn't allow the dashboard's port you get a HTTP 403 instead of the dashboard.
Re storage: We have a cluster with 10+ nodes, each with 5+ disks a 10 TB. How would you make sure that your software talks to the correct disk, after it gets restarted and may end up on another node?
Re limits: The highest goal is not avoiding ressource exhaustion, the highest goal is service continuity, though. It can all run on 100% and die. no problem. I just need to know that I should exchange the first few disks/processors/machines before the customer facing service slows down.
@storage If you want to move your disks with your containers you need an additional storage system(SAN, cloud provider or distributed storage in kubernetes). Then you create persistence volumes in kubernetes that references a disk from the storage provider. This allows you to assign this disk to a pod with a persistence volume claim. The disk that is linked to the container through persistent volume and persistent volume claim will be moved on the same node the container is scheduled. If you want to run stateful workloads on kubernetes I would advice you to use a storage system. You can use local disks but you loose some of the flexibility that you gain from kubernetes by tying your containers to certain nodes with the data. There is also work being done on improving the handling of local storage to treat it more like a resource and introduce separation by using local volume per kubernetes local disk volumes.
But it'll be alpha in 1.7: https://github.com/kubernetes/features/issues/121
Deis aimed (aims?) to be the lightweight version, but then got acquired by MS.
And the installation was just as confusing it seems.
I'm just asking because I was born in the 90's, I'm not very aware of the state of email server management then.