X axis is the horizontal scale out with adding more machines behind the load balancer. Microservice code is replicated behind the scenes on each machine to handle the traffic. An application doesn't much need to be aware about this type of scaling, typically handled by any TCP load balancer. The problem with this approach is that the application has a state to maintain and it needs lots of work to handle that, also it needs lots of cache work. Performance highly depends on the how cache and its algorithms are performing: