What is "Reverse Proxy" and "Load Balancing" in Nginx / Web server terms?

Question

These are two phrases I hear about very often, mainly associated with Nginx. Can someone give me a laymans defintion?

Answer 1

In simplest term:

A reverse proxy accepts a request from a client, forwards it to a server that can fulfill it, and returns the server’s response to the client.

A load balancer distributes incoming client requests among a group of servers, in each case returning the response from the selected server to the appropriate client.

But they sound pretty similar, right? Both types of application sit between clients and servers, accepting requests from the former and delivering responses from the latter. No wonder there’s confusion about what’s a reverse proxy vs. load balancer. To help tease them apart, let’s explore when and why they’re typically deployed at a website.

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Load Balancing

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Load balancers are most commonly deployed when a site needs multiple servers because the volume of requests is too much for a single server to handle efficiently. Deploying multiple servers also eliminates a single point of failure, making the website more reliable. Most commonly, the servers all host the same content, and the load balancer’s job is to distribute the workload in a way that makes the best use of each server’s capacity, prevents overload on any server, and results in the fastest possible response to the client.

Reverse Proxy

Whereas deploying a load balancer makes sense only when you have multiple servers, it often makes sense to deploy a reverse proxy even with just one web server or application server. You can think of the reverse proxy as a website’s “public face.” Its address is the one advertised for the website, and it sits at the edge of the site’s network to accept requests from web browsers and mobile apps for the content hosted at the website.

more details...

Answer 2

Definitions are often difficult to understand. I guess you just need some explanation for their use case.

A short explanation is: load balancing is one of the functionalities of reverse proxy, and reverse proxy is one of the softwares that can do load balancing.

And a long explanation is given below.

For example a service of your company has customers in UK and German. Because the policy is different for these two countries, your company has two web servers, uk.myservice.com for UK and de.myservice.com for German, each with different business logic. In addition, your company wants there to be only one unified endpoint, myservice.com for the service. In this case, you need to set up a reverse proxy as the unified endpoint. The proxy takes the url myservice.com, and rewrites the url of incoming requests so that requests from UK(determined by source ip) go to uk.myservice.com and requests from German go to de.myservice.com. From the view of a client from UK, it never knows the response is actually generated from uk.myservice.com.

In this case, the load of request traffic to the service is actually balanced to servers on uk.myservice.com and de.myservice.com as a side effect. So we normally don't call it used as a load balancer, just say it as a reverse proxy.

But lets say if your company uses the same policy for all countries, and has 2 servers, a.myservice.com and b.myservice.com, only for the reason that the work load is to heavy for one server machine. In this case, we normally call the reverse proxy as load balancer to emphasize the reason why it is being used.