Untitled :: ROSA Workshop

Introduction

When deploying your ROSA cluster, you can configure many aspects of your worker nodes, but what happens when you need to change your worker nodes after they’ve already been created? These activities include scaling the number of nodes, changing the instance type, adding labels or taints, just to name a few.

Many of these changes are done using Machine Pools. Machine Pools ensure that a specified number of Machine replicas are running at any given time. Think of a Machine Pool as a "template" for the kinds of Machines that make up the worker nodes of your cluster. If you’d like to learn more, see the Red Hat documentation on worker node management.

Here are some of the advantages of using ROSA Machine Pools to manage the size of your cluster

Scalability - A ROSA Machine Pool enables horizontal scaling of your cluster. It can easily add or remove worker nodes to handle the changes in workload. This flexibility ensures that your cluster can dynamically scale to meet the needs of your applications
High Availability - ROSA Machine Pools supports the creation of 3 replicas of workers across different availability zones. This redundancy helps ensure high availability of applications by distributing workloads.
Infrastructure Diversity - ROSA Machine Pools allow you to provision worker nodes of different instance types. This enables you to leverage the best kind of instance family for different workloads.
Integration with Cluster Autoscaler - ROSA Machine Pools seamlessly integrate with the Cluster Autoscaler feature, which automatically adjusts the number of worker nodes based on the current demand. This integration ensures efficient resource utilization by scaling the cluster up or down as needed, optimizing costs and performance.

Review the following digram to see the relationship between a Machine Pool, Machine Set, Machines, and Nodes.

Scaling worker nodes

Via the CLI

First, let’s see what Machine Pools already exist in our cluster. To do so, run the following command:

rosa list machinepools -c rosa-${GUID}

Sample Output

ID       AUTOSCALING  REPLICAS  INSTANCE TYPE  LABELS    TAINTS    AVAILABILITY ZONES    SUBNETS    SPOT INSTANCES
Default  No           2         m6a.xlarge                         us-east-2a                       N/A

Now, let’s take a look at the MachineSets inside of the ROSA cluster that have been created according to the instructions provided by the above MachinePools. To do so, run the following command:

oc -n openshift-machine-api get machinesets

Sample Output

NAME                                   DESIRED   CURRENT   READY   AVAILABLE   AGE
rosa-6n4s8-7hbhw-infra-us-east-2a      2         2         2       2           22h
rosa-6n4s8-7hbhw-worker-us-east-2a     2         2         2       2           23h

You will see two MachineSets, one for worker nodes and one for infra nodes.

Now, let’s take a look at the Machines inside of the ROSA cluster that have been created according to the instructions provided by the above MachineSets. To do so, run the following command:

oc -n openshift-machine-api get machine

Sample Output

NAME                                       PHASE     TYPE         REGION      ZONE         AGE
rosa-6n4s8-7hbhw-infra-us-east-2a-bgr86    Running   r5.xlarge    us-east-2   us-east-2a   22h
rosa-6n4s8-7hbhw-infra-us-east-2a-xthr6    Running   r5.xlarge    us-east-2   us-east-2a   22h
rosa-6n4s8-7hbhw-master-0                  Running   m6a.2xlarge  us-east-2   us-east-2a   23h
rosa-6n4s8-7hbhw-master-1                  Running   m6a.2xlarge  us-east-2   us-east-2a   23h
rosa-6n4s8-7hbhw-master-2                  Running   m6a.2xlarge  us-east-2   us-east-2a   23h
rosa-6n4s8-7hbhw-worker-us-east-2a-xc8g2   Running   m6a.xlarge   us-east-2   us-east-2a   22h
rosa-6n4s8-7hbhw-worker-us-east-2a-zxm8j   Running   m6a.xlarge   us-east-2   us-east-2a   22h

For this workshop, we’ve deployed your ROSA cluster with seven total machines (two workers, three control planes, and two infrastructure nodes).

Now that we know that we have two worker nodes, let’s create a MachinePool to add a new worker node using the ROSA CLI. To do so, run the following command:
```
rosa create machinepool -c rosa-${GUID} --replicas 1 --name workshop --instance-type m5.xlarge
```
Sample Output
```
I: Fetching instance types
I: Machine pool 'workshop' created successfully on cluster 'rosa-6n4s8'
I: To view all machine pools, run 'rosa list machinepools -c rosa-6n4s8'
```
This command adds a single m5.xlarge instance to the first AWS availability zone in the region your cluster is deployed in.
Now, let’s scale up our selected MachinePool from one to two machines. To do so, run the following command:
```
rosa update machinepool -c rosa-${GUID} --replicas 2 workshop
```
Sample Output
```
I: Updated machine pool 'workshop' on cluster 'rosa-6n4s8'
```

Now that we’ve scaled the MachinePool to two machines, we can see that the machine is already being created. First, let’s quickly check the output of the oc get machinesets command we ran earlier:

oc -n openshift-machine-api get machinesets

Sample Output

NAME                                   DESIRED   CURRENT   READY   AVAILABLE   AGE
rosa-6n4s8-7hbhw-infra-us-east-2a      2         2         2       2           22h
rosa-6n4s8-7hbhw-worker-us-east-2a     2         2         2       2           23h
rosa-6n4s8-7hbhw-workshop-us-east-2a   2         2                             70s

Note, that the number of *desired* and *current* nodes matches the scale we specified, but depending when you ran this command they may not be available yet.

We can also get the state of our machines to see the additional machines being provisioned:

oc -n openshift-machine-api get machine --watch

Sample Output

NAME                                         PHASE         TYPE         REGION      ZONE         AGE
rosa-6n4s8-7hbhw-infra-us-east-2a-bgr86      Running       r5.xlarge    us-east-2   us-east-2a   22h
rosa-6n4s8-7hbhw-infra-us-east-2a-xthr6      Running       r5.xlarge    us-east-2   us-east-2a   22h
rosa-6n4s8-7hbhw-master-0                    Running       m5.2xlarge   us-east-2   us-east-2a   23h
rosa-6n4s8-7hbhw-master-1                    Running       m5.2xlarge   us-east-2   us-east-2a   23h
rosa-6n4s8-7hbhw-master-2                    Running       m5.2xlarge   us-east-2   us-east-2a   23h
rosa-6n4s8-7hbhw-worker-us-east-2a-xc8g2     Running       m5.xlarge    us-east-2   us-east-2a   23h
rosa-6n4s8-7hbhw-worker-us-east-2a-zxm8j     Running       m5.xlarge    us-east-2   us-east-2a   23h
rosa-6n4s8-7hbhw-workshop-us-east-2a-pcfd9   Provisioned   m5.xlarge    us-east-2   us-east-2a   3m57s
rosa-6n4s8-7hbhw-workshop-us-east-2a-pxnvd   Provisioned   m5.xlarge    us-east-2   us-east-2a   4m30s

Let the above command run until all machines are in the Running phase. This means that they are ready and available to run Pods in the cluster. Hit CTRL-C to exit the oc command.
We don’t actually need these extra worker nodes so let’s scale the cluster back down to a total of 3 worker nodes by scaling down the "Workshop" Machine Pool. To do so, run the following command:
```
rosa update machinepool -c rosa-${GUID} --replicas 1 workshop
```

Now that we’ve scaled the MachinePool (and therefore the MachineSet) back down to one machine, we can see the change reflected in the cluster almost immediately. Let’s quickly check the output of the same command we ran before:

oc -n openshift-machine-api get machinesets

Sample Output

NAME                                   DESIRED   CURRENT   READY   AVAILABLE   AGE
rosa-6n4s8-7hbhw-infra-us-east-2a      2         2         2       2           22h
rosa-6n4s8-7hbhw-worker-us-east-2a     2         2         2       2           23h
rosa-6n4s8-7hbhw-workshop-us-east-2a   1         1         1       1           6m49s

Now let’s scale the cluster back down to a total of 2 worker nodes by deleting the "Workshop" Machine Pool. To do so, run the following command:
```
rosa delete machinepool -c rosa-${GUID} workshop --yes
```
Sample Output
```
I: Successfully deleted machine pool 'workshop' from cluster 'rosa-6n4s8'
```
You can validate that the MachinePool has been deleted by using the rosa cli:

rosa list machinepools -c rosa-${GUID}

+ .Sample Output

ID       AUTOSCALING  REPLICAS  INSTANCE TYPE  LABELS    TAINTS    AVAILABILITY ZONES    SUBNETS    SPOT INSTANCES
Default  No           2         m5.xlarge                          us-east-2a                       N/A

Congratulations! You’ve successfully scaled your cluster up and back down to two worker nodes.

Summary

Here you learned:

Creating a new Machine Pool for your ROSA cluster to add additional nodes to the cluster
Scaling your new Machine Pool up to add more nodes to the cluster
Scaling your Machine Pool down to remove worker nodes from the cluster