Misjudging incoming traffic can overload your web servers. Load balancers like HAProxy (High Availability Proxy) can help alleviate that issue. The primary job of load balancers is to balance the load on the server by minimizing response times, optimizing the usage of your resources, and improving the performance of your multi-server configuration.
A service mesh is an additional infrastructure layer that provides a means of communication between all services in a given application. It is typically deployed as a series of proxies alongside each service instance. Since the service mesh proxies are deployed alongside the application services and not as part of it, they are often referred to as sidecars. This means that as a whole, these sidecar proxies are a mesh network and an infrastructure layer separate from the application. A service mesh not only brokers communication between all services in an application but, since all requests, both internal and external, pass through it, it provides a means for handling many tasks that can be obfuscated away from the application.