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Gemini Example: CodiMD

Note: this will not work in a KIND cluster. It has been tested on DigitalOcean.

Install the controller

helm repo add fairwinds-stable https://charts.fairwinds.com/stable
helm install gemini fairwinds-stable/gemini --namespace gemini --create-namespace

Install CodiMD

helm repo add codimd https://helm.codimd.dev/
helm upgrade --install codimd codimd/codimd -n codimd --create-namespace --set codimd.imageStorePersistentVolume.enabled=false

This will create a PVC for the Postgres instance that drives CodiMD.

Set up the Backup Schedule

cat <<EOF | kubectl apply -f -
apiVersion: gemini.fairwinds.com/v1beta1
kind: SnapshotGroup
metadata:
  name: codimd-postgresql
  namespace: codimd
spec:
  persistentVolumeClaim:
    claimName: data-codimd-postgresql-0
  schedule:
    - every: "10 minutes"
      keep: 3
    - every: hour
      keep: 1
EOF

within 30 seconds or so, you should see a VolumeSnapshot:

$ kubectl get volumesnapshot -n codimd
NAME                           READYTOUSE   SOURCEPVC                  SOURCESNAPSHOTCONTENT   RESTORESIZE   SNAPSHOTCLASS      SNAPSHOTCONTENT                                    CREATIONTIME   AGE
codimd-postgresql-1677262979   true         data-codimd-postgresql-0                           8Gi           do-block-storage   snapcontent-3aff5b51-e0c1-4154-bd93-4b396bf0c16e   12m            12m

Create a document

kubectl port-forward svc/codimd 3000:80 -n codimd

Visit localhost:3000 and sign up for an account. (You can use a dummy email. Make sure to click Register instead of hitting enter when first signing up.) Create a new note and enter some text.

Trigger a backup

Rather than waiting for Gemini to create the next backup, you can delete existing backups, and Gemini will create a new one.

kubectl delete volumesnapshot --all -n codimd

Within 30 seconds, you should see new snapshots appear. Make sure to wait until READYTOUSE is true

$ kubectl get volumesnapshot -n codimd
NAME                           READYTOUSE   SOURCEPVC                  SOURCESNAPSHOTCONTENT   RESTORESIZE   SNAPSHOTCLASS      SNAPSHOTCONTENT                                    CREATIONTIME   AGE
codimd-1594929516              true         codimd                                             2Gi           do-block-storage   snapcontent-e75421c6-c4ca-4bbf-81f4-a2fb0706b957   5s             7s
codimd-postgresql-1594929517   true         data-codimd-postgresql-0                           8Gi           do-block-storage   snapcontent-ad71c1f8-af7b-4cdc-85ba-e512a77095a3   4s             6s

Edit your document again

kubectl port-forward svc/codimd 3000:80 -n codimd

Go back to your document (if you lost it, you can find it again by going to localhost:3000 and clicking History).

Delete what you wrote and replace it with something else. These changes will get reverted when we restore.

Perform the restore

First, we need to scale down our deployment. We can't swap out a PVC in-place, so you'll necessarily incur some downtime.

kubectl scale all --all --replicas=0 -n codimd

Next, annotate the SnapshotGroup with the timestamp of the snapshot you want.

For example, here we'll use timestamp 1585945609.

$ kubectl get volumesnapshot -n codimd
NAME                           AGE
codimd-1585945609              15s
codimd-postgresql-1585945609   15s
kubectl annotate snapshotgroup/codimd-postgresql -n codimd --overwrite \
  "gemini.fairwinds.com/restore=1585945609"

This will:

  • create a one-off backup of your PVC
  • delete the PVC
  • create a new PVC with the same name from your snapshot

Note: If your PVC gets stuck in Terminating, this might be related to rate-limiting from the DO API (check this issue for more info) You can force destroy the PVC by running:

kubectl -n codimd patch pvc data-codimd-postgresql-0 -p '{"metadata":{"finalizers": []}}' --type=merge

Wait until you see that your PVC is back in Bound state.

Finally, we can scale back up:

kubectl scale all --all --replicas=1 -n codimd

Verify the restore

kubectl port-forward svc/codimd 3000:80 -n codimd

Go back to your document. The second round of edits you made should be gone!