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TopoLVM on Kubernetes

TopoLVM is like Local Path Provisioner, in that it deals with local volumes specific to each Kubernetes node, but it offers more flexibility, and is more suited for a production deployment.


Additional benefits offered by TopoLVM are:

  • Volumes can by dynamically expanded
  • The scheduler is capacity-aware, and can schedule pods to nodes with enough capacity for the pods' storage requirements
  • Multiple storageclasses are supported, so you could, for example, create a storageclass for HDD-backed volumes, and another for SSD-backed volumes


Volume Group

Finally you get to do something on your nodes without YAML or git, like a pre-GitOps, bare-metal-cavemonkey! 🐡

On each node, you'll need an LVM Volume Group (VG) for TopoLVM to consume. The most straightforward to to arrange this is to dedicate a disk to TopoLVM, and create a dedicated PV and VG for it.

In brief, assuming /dev/sdb is the disk (and it's unused), you'd do the following to create a VG called VG-topolvm:

pvcreate /dev/sdb
vgcreate VG-topolvm /dev/sdb


If you don't have a dedicated disk, you could try installing your OS using LVM partitioning, and leave some space unused, for TopoLVM to consume. Run vgs from an installed node to work out what the VG name is that the OS installer chose.


We need a namespace to deploy our HelmRelease and associated ConfigMaps into. Per the flux design, I create this example yaml in my flux repo:

apiVersion: v1
kind: Namespace
  name: topolvm-system


Next, we need to define a HelmRepository (a repository of helm charts), to which we'll refer when we create the HelmRelease. We only need to do this once per-repository. In this case, we're using the official TopoLVM helm chart, so per the flux design, I create this example yaml in my flux repo:

kind: HelmRepository
  name: topolvm
  namespace: flux-system
  interval: 15m


Now that the "global" elements of this deployment (Namespace and HelmRepository) have been defined, we do some "flux-ception", and go one layer deeper, adding another Kustomization, telling flux to deploy any YAMLs found in the repo at /topolvm. I create this example Kustomization in my flux repo:

kind: Kustomization
  name: topolvm--topolvm-system
  namespace: flux-system
  interval: 15m
  path: ./topolvm-system
  prune: true # remove any elements later removed from the above path
  timeout: 2m # if not set, this defaults to interval duration, which is 1h
    kind: GitRepository
    name: flux-system
    - apiVersion: apps/v1
      kind: Deployment
      name: topolvm-controller
      namespace: topolvm-system
    - apiVersion: apps/v1
      kind: DaemonSet
      name: topolvm-lvmd-0
      namespace: topolvm-system
    - apiVersion: apps/v1
      kind: DaemonSet
      name: topolvm-node
      namespace: topolvm-system
    - apiVersion: apps/v1
      kind: DaemonSet
      name: topolvm-scheduler
      namespace: topolvm-system

What's with that screwy name?

Why'd you call the kustomization topolvm--topolvm-system?

I keep my file and object names as consistent as possible. In most cases, the helm chart is named the same as the namespace, but in some cases, by upstream chart or historical convention, the namespace is different to the chart name. TopoLVM is one of these - the helmrelease/chart name is topolvm, but the typical namespace it's deployed in is topolvm-system. (Appending -system seems to be a convention used in some cases for applications which support the entire cluster). To avoid confusion when I list all kustomizations with kubectl get kustomization -A, I give these oddballs a name which identifies both the helmrelease and the namespace.


Now we're into the topolvm-specific YAMLs. First, we create a ConfigMap, containing the entire contents of the helm chart's values.yaml. Paste the values into a values.yaml key as illustrated below, indented 4 spaces (since they're "encapsulated" within the ConfigMap YAML). I create this example yaml in my flux repo:

apiVersion: v1
kind: ConfigMap
  creationTimestamp: null
  name: topolvm-helm-chart-value-overrides
  namespace: topolvm-system
  values.yaml: |-
    # paste chart values.yaml (indented) here and alter as required>

That's a lot of unnecessary text!

Why not just paste in the subset of values I want to change?

You know what's harder than working out which values from a 2000-line values.yaml to change?

Answer: Working out what values to change when the upstream helm chart has refactored or added options! By pasting in the entirety of the upstream chart, when it comes time to perform upgrades, you can just duplicate your ConfigMap YAML, paste the new values into one of the copies, and compare them side by side to ensure your original values/decisions persist in the new chart.

Then work your way through the values you pasted, and change any which are specific to your configuration. You might want to start off by changing the following to match the name of the volume group you created above.1

  # lvmd.managed -- If true, set up lvmd service with DaemonSet.
  managed: true

  # lvmd.socketName -- Specify socketName.
  socketName: /run/topolvm/lvmd.sock

  # lvmd.deviceClasses -- Specify the device-class settings.
    - name: ssd
      volume-group: myvg1
      default: true
      spare-gb: 10


Lastly, having set the scene above, we define the HelmRelease which will actually deploy TopoLVM into the cluster, with the config we defined above. I save this in my flux repo:

kind: HelmRelease
  name: topolvm
  namespace: topolvm-system
      chart: topolvm
      version: 3.x
        kind: HelmRepository
        name: topolvm
        namespace: flux-system
  interval: 15m
  timeout: 5m
  releaseName: topolvm
  - kind: ConfigMap
    name: topolvm-helm-chart-value-overrides
    valuesKey: values.yaml # This is the default, but best to be explicit for clarity
Why not just put config in the HelmRelease?

While it's true that we could embed values directly into the HelmRelease YAML, this becomes unweildy with large helm charts. It's also simpler (less likely to result in error) if changes to HelmReleases, which affect deployment of the chart, are defined in separate files to changes in helm chart values, which affect operation of the chart.


Deploy TopoLVM

Having committed the above to your flux repository, you should shortly see a topolvm kustomization, and in the topolvm-system namespace, a bunch of pods:

demo@shredder:~$ kubectl get pods -n topolvm-system
NAME                                  READY   STATUS    RESTARTS   AGE
topolvm-controller-85698b44dd-65fd9   4/4     Running   0          133m
topolvm-controller-85698b44dd-dmncr   4/4     Running   0          133m
topolvm-lvmd-0-98h4q                  1/1     Running   0          133m
topolvm-lvmd-0-b29t8                  1/1     Running   0          133m
topolvm-lvmd-0-c5vnf                  1/1     Running   0          133m
topolvm-lvmd-0-hmmq5                  1/1     Running   0          133m
topolvm-lvmd-0-zfldv                  1/1     Running   0          133m
topolvm-node-6p4qz                    3/3     Running   0          133m
topolvm-node-7vdgt                    3/3     Running   0          133m
topolvm-node-mlp4x                    3/3     Running   0          133m
topolvm-node-sxtn5                    3/3     Running   0          133m
topolvm-node-xf265                    3/3     Running   0          133m
topolvm-scheduler-jlwsh               1/1     Running   0          133m
topolvm-scheduler-nj8nz               1/1     Running   0          133m
topolvm-scheduler-tg72z               1/1     Running   0          133m

How do I know it's working?

So the controllers etc are running, but how do we know we can actually provision volumes?

Create PVC

Create a PVC, by running:

cat <<EOF | kubectl create -f -
apiVersion: v1
kind: PersistentVolumeClaim
  name: topolvm-pvc
    - ReadWriteOnce
  storageClassName: topolvm-provisioner
      storage: 128Mi

Examine the PVC by running kubectl describe pvc topolvm-pvc

Create Pod

Now create a pod to consume the PVC, by running:

cat <<EOF | kubectl create -f -
apiVersion: v1
kind: Pod
  name: topolvm-test
  - name: volume-test
    image: nginx:stable-alpine
    imagePullPolicy: IfNotPresent
    - name: topolvm-rocks
      mountPath: /data
    - containerPort: 80
  - name: topolvm-rocks
      claimName: topolvm-pvc

Examine the pod by running kubectl describe pod topolvm-test.

Clean up

Assuming that the pod is in a Running state, then TopoLVM is working!

Clean up your mess, little bare-metal-cave-monkey 🐡, by running:

kubectl delete pod topolvm-test
kubectl delete pvc topolvm-pvc


Are things not working as expected? Try one of the following to look for issues:

  1. Watch the lvmd logs, by running kubectl logs -f -n topolvm-system -l
  2. Watch the node logs, by running kubectl logs -f -n topolvm-system -l
  3. Watch the scheduler logs, by running kubectl logs -f -n topolvm-system -l
  4. Watch the controller node logs, by running kubectl logs -f -n topolvm-system -l

Chef's notes πŸ““

  1. This is where you'd add multiple Volume Groups if you wanted a storageclass per Volume Group ↩

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