Hacker News Reader

Comment by elktea | Hacker News Reader

Is anyone else very wary about keeping things with persistent state in containers (like databases)?

The persistent state is really just the data, not the process. With kubernetes you store the data on a persistent volume (which could be EBS, iSCSI, etc) and the process runs in the container. Host dies? Kubernetes can re-attach that volume on another host, start up a new container and you are back in business.

*Note: looks like in this example they are not setting up a persistent volume.

> Kubernetes can re-attach that volume on another host, start up a new container and you are back in business.

There are still some bugs with this, particularly on AWS. Getting better with every release, though.

We just played with Elastic File System mounted into a Pod via `nfs` and it worked like a charm, with the additional "oh, wow" of being able to attach the same EFS to several Pods at the same time. I was also thrilled that they mounted with the root uid intact so there wasn't any kind of dumb permission juggling.

I did say "played with" because we haven't beat on it to know if one could run Jira, Gitlab, Prometheus, that kind of workload. I wouldn't at this point try Postgres but maybe it'd work.

I use my postgres with EBS though.

I wonder how suitable EFS is for Postgres. It's supposedly low-latency, high-throughput and supports Unix locking semantics and so on. On the other hand, it's NFS (one of the worst protocols out there), and there have been reports of less than impressive latencies. EFS is also a lot more expensive than EBS.

EFS is also a lot more expensive than EBS.

That may be true, but getting a k8s cluster unwedged from EBS volume state mismanagement is expensive, too.

What I really want is the hutzpah to run GlusterFS but I am not yet brave enough to be in the keeping-a-production-FS-alive business.

Can you elaborate? I run my postgres on k8s with EBS.

Probably the most severe issue: https://github.com/kubernetes/kubernetes/issues/29324. You won't encounter it until a pod is rescheduled, though.

Another strategy is to use https://github.com/wal-e/wal-e to continuously backup and restore from S3 on boot (e.g. https://github.com/deis/postgres). But restores will be slower and it probably doesn't come with strong durability guarantees.

Ideally, yes. It's not actually the case though. Again, ideally.

Well tested databases have evolved to have to survive arbitrary power cuts- even in the middle of a transaction; and so have slowly become reliable enough to trust to start from on-disk state only.

Good f-in' luck bringing your db flavor of the month back online from disk state alone. Hope you didn't have any transactions open to your DB before it got rescheduled to a different node in your cluster.

I work at a shop that has everything in docker containers. We have mostly coreos clusters, but we're slowly moving to mesos/marathon.

And I do mean everything. We've got .NET apps running in docker containers, perl scripts .. they went hard in on docker.

But our databases: Amazon RDS instances.

It's one of the few things that isn't dockerized.

I've personally been looking at a lot of docker solutions for my own projects and I'm still weary of a lot of the data storage solutions out there.

What .net are you running on containers? Mono? .Net Core? Is it working for you well outside of Windows server?

.NET core on Linux (not Mono). I'm not sure of the details; haven't looked at that particular project yet.

Reply on news.ycombinator.com