HAProxy

It prevents a single server failure from being a downtime event by adding redundancy to every layer of your architecture. A load balancer facilitates redundancy for the backend layer (web/app servers), but for a true high availability setup, you need to have redundant load balancers as well. So it is well suited for all production related servers and less suited for individual servers that do not require redundancy.

In our company, we use the HA Proxy to balance internal applications or external applications with a number of connections that are not too excessive. For critical applications or with a huge number of connections we use a hardware balancer. In this way, we manage to minimize the economic costs of the infrastructures.

Anytime you need to balance load or direct traffic based on rule sets, either at the edge or internally, HAProxy is the perfect solution.

HAProxy is useful for both level 4 and level 7 load balancing, SSL termination, etc. It is a software load balancer, so it is not good in cases where we need a hardware load balancing to solve our business problems. It is a bit memory intensive, so we need to watch out for it.

I've had good experiences with most things that I've attempted using HAProxy. About the only thing I haven't tried yet is setting up an HA Pair using VRRP which I just found out is even a possibility. But it does great at terminating SSL on HTTPS VIPs which is most of what I've used it for, About the only thing I haven't figured out yet is one specific use case I have setup on a pair of F5s for syslog forwarding to multiple destinations, but I also haven't spent a ton of time looking into it since I think there's a limitation with UDP traffic and HAProxy.

HAProxy is a lightweight load balancer that just works. It requires a minimal footprint and really just works once set up correctly. It can balance a web app, APIs, database connections and more. I've used competing products that just don't compete with HAProxy in my experience. The community version is rock solid, as is the enterprise edition.

For an open source load balancer, this is great. Works easily out of the box. Configuration is what will take the longest amount of time. But it will expose you to how a load balancer works.