A load balancer is not a WAF, nor is it a CDN, but it works well with both!
A load balancer is a device that sits between your website and the outside world and distributes load across one or more compute nodes. I have seen performance benefits from using a load balancer with only one node, but often this is just one part of a more complicated infrastructure that spans multiple systems with many interconnecting parts.
In contrast to a WAF (Web Application Firewall) the primary purpose of a load balancer is not to scrub traffic before it hits the compute nodes, but in a way that is one of the added benefits. While not performing content level checks a load balancer will efficiently disregard most junk request data helping to mitigate DOS and DDOS attacks, we can also offload SSL termination to the load balancer freeing up whole milliseconds from the compute nodes to compute their primary compute harder. The load balancer also can act as a static edge device furthering your precious internal compute and data clusters from the dangerous outside web.
Now a CDN also makes your assets load faster, but in a somewhat different way from a load balancer. A CDN takes the load off your primary servers by providing a cached copy of your static assets on many servers around the world, hoping to have a faster closer node to your visitor increasing the speed and parallel nature that your site loads. In some cases, this can dramatically improve loading times and lower your hosting bills, but a CDN is less useful with dynamic content. In contrast to a CDN, a load balancer takes incoming requests from the web and proxies them to pre-configured resource clusters spreading the load internally but not often geographically.
In a monolithic architecture, the load balancer is represented as the web server (Often Apache or Nginx) relaying traffic to the scripting language (PHP, Ruby, node, etc). Our web server is able to handle hundreds or thousands of requests depending on the configuration, but eventually, it makes sense to scale to more systems rather than larger systems, and that is where Load Balances shine!
If you need any assistance or have a question, please reach out to us. We can be reached in a variety of ways.