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Comment by rad_gruchalski | Hacker News Reader

> Both. Containers are meant to be ephemeral, they don't play well with permanent storage by design. People have been trying to run databases anyway and hitting roadblock after roadblock.

Really? Can you share details? I'm asking because I know people who run databases in Docker for years and have no issues. Just store data on a volume.

> Here's an old rant mentioning broken container filesystems, a bit old from 2016 but storage didn't change much

Maybe not, haven't had a storage issue with Docker myself since maybe 2017. That article feels like a big rant but yes, it's ... old.

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Docker volumes are great. I've also run databases in docker without issue. But they're different from kubernetes "persistent volumes" and "persistent volume claims"

The issues come when you move into high availability (specifically in a Kubernetes context). K8s may decide to move your database to a different node (server) on a whim, and suddenly your data is gone. You have to solve this by having mounted, block-level storage available to your cluster (eg AWS's EBS; the product being discussed) so you can use persistent volumes. That comes with added complexity, and usually the need to incorporate db operators into your stack.

As a result, a lot of k8s admins (myself included) choose to pay crazy amounts for RDS and S3 to avoid the complexities of persistent data.

I'm just learning all this; but couldn't you run a DB Cluster persistently on EC2, managed separately from K8s, and VPC it to the K8s cluster? Is there transfer charges involved and/or is the latency to night to consider a setup like this? Is this cost effective to RDS?

If you have a DB cluster running on multiple EC2 instances, you can definitely do that. There are advantages/disadvantages compared to just paying for RDS (eg managing backups, system complexity, and failover) but if you already have that expertise in-house, I can imagine a scale where there might be cost savings.

My comment was specifically discussing the challenges of keeping block storage-dependent, stateful apps within k8s (as opposed to using RDS or rolling your own HA cluster on EC2 or elsewhere). Apologies to GP if I incorrectly assumed they were discussing container volumes more broadly.

Yes, hence „volume”, not „docker volume”. For k8s, always a PV. rexray for mesos.

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