I started wso2 elb server and it is not auto scaling and showing the following error,
You cannot auto scale just by changing the configurations in WSO2 ELB. See Auto-Scaling in Load Balancer .
You need to configure cartridges for your preferred IaaS. ELB supports Amazon EC2 and OpenStack. Cartidge is basically an image (for example an AMI in EC2) and ELB can spawn instances from the configured image. In the image, you need to configure how to connect to existing WSO2 product cluster and do other required configurations.
However as I mentioned in other Stack Overflow answer, WSO2 ELB is no longer recommended and it has been discontinued.
We recommend WSO2 Private PaaS if you need an auto-scaling platform with WSO2 products. With WSO2 Private PaaS, You will get most of the frequently used WSO2 products as cartridges.