Scaling your Luna Streaming cluster

This page will show you how to scale Luna Streaming clusters up for more compute capacity, or down for less.

The Kubernetes Autoscaling for Apache Pulsar (KAAP) operator takes care of scaling Pulsar cluster components, deploying new clusters, and even migrating your existing cluster to an operator-managed deployment.

Installing Pulsar cluster

For our Pulsar cluster installation, use this Helm chart.

To start the cluster, use the values provided in this YAML file.

$ diff ~/dev-values.yaml ~/dev-values_large.yaml
40c40,47
<   replicaCount: 1
---
>   replicaCount: 4
>   volumes:
>     journal:
>       size: 2Gi
>     ledgers:
>       size: 10Gi
>     ranges:
>       size: 1Gi
52,54c59,61
<     defaultEnsembleSize: 1
<     defaultAckQuorum: 1
<     defaultWriteQuorum: 1
---
>     defaultEnsembleSize: 3
>     defaultAckQuorum: 2
>     defaultWriteQuorum: 3

Create the cluster by installing Pulsar with dev-values_large.yaml:

$ helm install pulsar -f ~/dev-values_large.yaml --wait datastax-pulsar/pulsar

Generating data

Generate data in your namespaces:

$ bin/pulsar-admin namespaces set-retention public/default -t -1 -s 100M
$ bin/pulsar-client produce test1 -n 500 -m "sdasdsdsadsadsad"
$ bin/pulsar-client produce test2 -n 500 -m "sdasdsdsadsadsad"
$ bin/pulsar-client produce test3 -n 500 -m "sdasdsdsadsadsad"

Ensure all bookies have some ledgers assigned to them:

$ ./bin/bookkeeper shell listledgers -meta | grep pulsar-bookkeeper-3

Downscaling bookies

To downscale a bookie, change the replicaCount value in the YAML file to a number less than the current replicaCount:
```
 bookkeeper:
    replicaCount: 3
```
Upgrade the Helm chart to use the new value:
```
$ helm upgrade pulsar -f ~/dev-values_large.yaml --wait datastax-pulsar/pulsar
```
Now, bookkeeper-3 will fail to start with org.apache.bookkeeper.bookie.BookieException$InvalidCookieException.
Destroy the bookie’s PVC:

$ kubectl delete pvc pulsar-bookkeeper-ledgers-pulsar-bookkeeper-3

Scaling up your cluster

To scale up your cluster, change the replicaCount value in the YAML file to a number greater than the current replicaCount:

 bookkeeper:
    replicaCount: 5

Upgrade the Helm chart to use the new value in the Pulsar cluster:

$ helm upgrade pulsar -f ~/dev-values_large.yaml --wait datastax-pulsar/pulsar

Recovering from a lost Persistent Volume Claim (PVC)

If a PVC goes down, track under-replicated ledgers from any live bookie:
```
$ ./bin/bookkeeper shell listunderreplicated
```
Double-check the bookie id of the failing bookie:
```
$ ./bin/bookkeeper shell listbookies -a
```
This command will return Cannot resolve pulsar-bookkeeper-3.pulsar-bookkeeper.default.svc.cluster.local:3181, bookie is unknown.
Decommission the bookie:
```
$ ./bin/bookkeeper shell decommissionbookie -bookieid pulsar-bookkeeper-3.pulsar-bookkeeper.default.svc.cluster.local:3181
```
The decommissioning will take some time because it triggers the audit and auto-recovery and blocks until auto-recovery completes.

This command will delete the cookie of the decommissioned bookie: pulsar-bookkeeper-3.pulsar-bookkeeper.default.svc.cluster.local:3181.
Restart the failing bookie with Ctrl-K in Kubernetes, or wait for Kubernetes to restart the bookie again.

The bookie will restart and rejoin the cluster. As expected with deleted PVC, data is lost.