Tag Archives: kubernetes

Longhorn in a Sandbox

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In my last post, I wrote about how I taught sesdev (originally a tool for deploying Ceph clusters on virtual machines) to deploy k3s, because I wanted a little sandbox in which I could break learn more about Kubernetes. It’s nice to be able to do a toy deployment locally, on a bunch of VMs, on my own hardware, in my home office, rather than paying to do it on someone else’s computer. Given the k3s thing worked, I figured the next step was to teach sesdev how to deploy Longhorn so I could break that learn more about that too.

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Teaching an odd dog new tricks

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We – that is to say the storage team at SUSE – have a tool we’ve been using for the past few years to help with development and testing of Ceph on SUSE Linux. It’s called sesdev because it was created largely for SES (SUSE Enterprise Storage) development. It’s essentially a wrapper around vagrant and libvirt that will spin up clusters of VMs running openSUSE or SLES, then deploy Ceph on them. You would never use such clusters in production, but it’s really nice to be able to easily spin up a cluster for testing purposes that behaves something like a real cluster would, then throw it away when you’re done.

I’ve recently been trying to spend more time playing with Kubernetes, which means I wanted to be able to spin up clusters of VMs running openSUSE or SLES, then deploy Kubernetes on them, then throw the clusters away when I was done, or when I broke something horribly and wanted to start over. Yes, I know there’s a bunch of other tools for doing toy Kubernetes deployments (minikube comes to mind), but given I already had sesdev and was pretty familiar with it, I thought it’d be worthwhile seeing if I could teach it to deploy k3s, a particularly lightweight version of Kubernetes. Turns out that wasn’t too difficult, so now I can do this:

> sesdev create k3s
=== Creating deployment "k3s" with the following configuration === 
Deployment-wide parameters (applicable to all VMs in deployment):
deployment ID:    k3s
number of VMs:    5
version:          k3s
OS:               tumbleweed
public network:   10.20.190.0/24 
Proceed with deployment (y=yes, n=no, d=show details) ? [y]: y
=== Running shell command ===
vagrant up --no-destroy-on-error --provision
Bringing machine 'master' up with 'libvirt' provider...
Bringing machine 'node1' up with 'libvirt' provider...
Bringing machine 'node2' up with 'libvirt' provider...
Bringing machine 'node3' up with 'libvirt' provider...
Bringing machine 'node4' up with 'libvirt' provider...

[...
  wait a few minutes
  (there's lots more log information output here in real life)
...]

=== Deployment Finished ===
 You can login into the cluster with:
 $ sesdev ssh k3s

…and then I can do this:

> sesdev ssh k3s
Last login: Fri Mar 24 11:50:15 CET 2023 from 10.20.190.204 on ssh
Have a lot of fun…

master:~ # kubectl get nodes
NAME     STATUS   ROLES                  AGE     VERSION
master   Ready    control-plane,master   5m16s   v1.25.7+k3s1
node2    Ready                     2m17s   v1.25.7+k3s1
node1    Ready                     2m15s   v1.25.7+k3s1
node3    Ready                     2m16s   v1.25.7+k3s1
node4    Ready                     2m16s   v1.25.7+k3s1 

master:~ # kubectl get pods -A
NAMESPACE     NAME                                      READY   STATUS      RESTARTS   AGE
kube-system   local-path-provisioner-79f67d76f8-rpj4d   1/1     Running     0          5m9s
kube-system   metrics-server-5f9f776df5-rsqhb           1/1     Running     0          5m9s
kube-system   coredns-597584b69b-xh4p7                  1/1     Running     0          5m9s
kube-system   helm-install-traefik-crd-zz2ld            0/1     Completed   0          5m10s
kube-system   helm-install-traefik-ckdsr                0/1     Completed   1          5m10s
kube-system   svclb-traefik-952808e4-5txd7              2/2     Running     0          3m55s
kube-system   traefik-66c46d954f-pgnv8                  1/1     Running     0          3m55s
kube-system   svclb-traefik-952808e4-dkkp6              2/2     Running     0          2m25s
kube-system   svclb-traefik-952808e4-7wk6l              2/2     Running     0          2m13s
kube-system   svclb-traefik-952808e4-chmbx              2/2     Running     0          2m14s
kube-system   svclb-traefik-952808e4-k7hrw              2/2     Running     0          2m14s

…and then I can make a mess with kubectl apply, helm, etc.

One thing that sesdev knows how to do is deploy VMs with extra virtual disks. This functionality is there for Ceph deployments, but there’s no reason we can’t turn it on when deploying k3s:

> sesdev create k3s --num-disks=2
> sesdev ssh k3s
master:~ # for node in \
    $(kubectl get nodes -o 'jsonpath={.items[*].metadata.name}') ;
    do echo $node ; ssh $node cat /proc/partitions ; done
master
major minor  #blocks  name
 253        0   44040192 vda
 253        1       2048 vda1
 253        2      20480 vda2
 253        3   44016623 vda3
node3
major minor  #blocks  name
 253        0   44040192 vda
 253        1       2048 vda1
 253        2      20480 vda2
 253        3   44016623 vda3
 253       16    8388608 vdb
 253       32    8388608 vdc
node2
 major minor  #blocks  name
 253        0   44040192 vda
 253        1       2048 vda1
 253        2      20480 vda2
 253        3   44016623 vda3
 253       16    8388608 vdb
 253       32    8388608 vdc
node4
 major minor  #blocks  name
 253        0   44040192 vda
 253        1       2048 vda1
 253        2      20480 vda2
 253        3   44016623 vda3
 253       16    8388608 vdb
 253       32    8388608 vdc
node1
 major minor  #blocks  name
 253        0   44040192 vda
 253        1       2048 vda1
 253        2      20480 vda2
 253        3   44016623 vda3
 253       16    8388608 vdb
 253       32    8388608 vdc

As you can see this gives all the worker nodes an extra two 8GB virtual disks. I suspect this may make sesdev an interesting tool for testing other Kubernetes based storage systems such as Longhorn, but I haven’t tried that yet.

An S3 Storage Experiment

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My team at SUSE is working on a new S3-compatible storage solution for Kubernetes, based on Ceph’s RADOS Gateway (RGW), except without any of the RADOS bits. The idea is that you can deploy our s3gw container on top of Longhorn (which provides the underlying replicated storage), and all this is running in your Kubernetes cluster, along with your applications which thus have convenient access to a local S3-compatible object store.

We’ve done this by adding a new storage backend to RGW. The approach we’ve taken is to use SQLite for metadata, with object data stored as files in a regular filesystem. This works quite neatly in a Kubernetes cluster with Longhorn, because Longhorn can provide a persistent volume (think: an ext4 filesystem), on which s3gw can store its SQLite database and object data files. If you’d like to kick the tyres, check out Giuseppe’s deployment tutorial for the 0.2.0 release, but bear in mind that as I’m writing this we’re all the way up to 0.4.0 so some details may have changed.

While s3gw on Longhorn on Kubernetes remains our primary focus for this project, the fact that this thing only needs a filesystem for backing storage means it can be run on top of just about anything. Given “just about anything” includes an old school two node Pacemaker cluster with DRBD for replicated storage, why not give that a try? I kinda like the idea of a good solid highly available S3-compatible storage solution that you could shove into the bottom of a rack somewhere without too much difficulty.

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