High Availability microk8s iSCSI storage

Ipolit · 03-25-2021, 01:12 AM

Hello,
I started to experiment with mickrok8s. I want to build HA system with iSCSI storage for the containers.
My question is how should I proceed with the storage
- Should I attach to hosts iSCSI storage or I have to attach it to each container I install.
Thank you in advance.

Gad · 03-25-2021, 01:58 AM

Best to keep the storage separate from the systems similar to a SAN / LUN. If one of the systems go down the other systems will still have access to the storage

Ipolit · 03-25-2021, 02:07 AM

Thank you, Gad,
I understand this and thus I want to use iSCSI share from separated SAN. My question is should I add a single LUN from the SAN to the hosts which run microk8s (Kubernetes) or I have to create containers inside microk8s and attach to them storage from the SAN.

Gad · 03-25-2021, 02:42 AM

I am not expert on this specific topic but what I have come to understand is that there should be a connection to each container.

Ipolit · 03-25-2021, 03:45 AM

I found an interesting article https://rootfs.github.io/iSCSI-Kubernetes/

The most interesting part is

Quote:

Persisting data inside a container can be done in two ways.

Container sets up iSCSI session
The iSCSI session is initiated inside the container, iSCSI traffic goes through Docker NAT to external iSCSI target. This approach doesn't require host's support and is thus portable. However, the Container is likely to suffer from suboptimal network performance, because Docker NAT doesn't deliver good performance, as reseachers at IBM found.

Since iSCSI is highly senstive to network performance, delay or jitters will cause iSCSI connection timeout and retries. This approach is thus not preferred for mission-critical services.

Host sets up iSCSI session
Host initiates the iSCSI session, attaches iSCSI disk, mounts the filesystem on the disk to a local directory, and shares the filesystem with Container. This approach doesn't need Docker NAT and is conceivably higher performing than the first approach.

So obviously the storage should be added to the hosts, this way multipath could be configured easy.
But the directory structure on all nodes (mount points) should be same.

Gad · 03-25-2021, 05:38 AM

Makes sense, if I compare it to non cluster / container environments the hosts make a connection to the SAN