You're running a single node Aria Operations for Logs deployment and would like to expand it, let's make it a 3-node cluster, supported configurations can be found here. To do that, deploy a new Aria Operations for Logs appliance and join it to an existing deployment, documentation here.
I've downloaded the appropriate binary and deployed my appliance, let's now access the UI for Setup.
click JOIN EXISTING DEPLOYMENT. Here you will need the FQDN of your Primary Node and a Secure Join Token which can be generated on your existing Primary Node from Management - Cluster - GENERATE JOIN TOKEN.
Click GO, which will initialize your new Worker Node.
After a few minutes, back on the Primary Node, you can see that the Worker Node has joined the Cluster.
As indicated, 2-node clusters are not supported, so let's add another one, same steps as above.
Back on the Primary Node UI, you can now see we have a 3-Node Cluster.
Aria Operations for Logs is a powerful platform, check it out!