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Reverse proxy vs. load balancer: How do they compare?
If reverse proxies were plantains, load balancers would be bananas. Despite surface similarities, the two services work in different ways and support varying use cases.
Just as bananas and plantains look similar and some recipes might permit the substitution of one for the other, reverse proxies and load balancers share overlapping functionality -- but their implementation depends on an application's requirements.
Both techniques can manage application requests and improve performance. However, reverse proxies and load balancers offer distinct capabilities that can address specific operational concerns and, as a result, align better with certain use cases.
What is a reverse proxy?
A reverse proxy is a service that accepts application requests from clients and forwards them to individual back-end servers that host the applications responsible for processing the requests.
Reverse proxies typically have their own IP address and, from the perspective of clients, are indistinguishable from the back-end servers they sit in front of. In other words, the proxy appears to be an ordinary application service that accepts requests from clients. The client has no way of knowing that the reverse proxy operates as an intermediary between them and the applications. In fact, a primary benefit of a reverse proxy architecture is that it facilitates the flexible management of incoming requests without requiring clients to change how they submit requests or how servers receive and process them.
Reverse proxies can perform various actions before passing requests onto an application. These actions might include the following:
- Inspecting data to analyze the contents of the request. For instance, the proxy could determine the type of request and whether it's appropriate for the intended application.
- Modifying data to conform with formatting standards or requirements. For example, the proxy might reformat parts of a request's URL content to ensure that the receiving application is capable of processing it.
- Enforcing security policies. For example, a reverse proxy can block a request if it determines the request is malicious.
Reverse proxies vs. forward proxies and API gateways
Forward proxies and API gateways can also act as intermediaries between clients and servers, but it is important to understand how they differ from reverse proxies.
Forward proxies collect requests from multiple clients, then forward them to the internet or relevant resources. They sit in front of clients and manage their outbound requests. Reverse proxies work the opposite way. They sit in front of servers and process incoming client requests before relaying them to the appropriate server.
An API gateway specializes in the management of API calls. Comparatively, reverse proxies can manage any application or server request.
What is a load balancer?
A load balancer is a hardware device or software service that accepts application requests from clients and distributes them across multiple application instances or back-end servers. Its main purpose is to dynamically distribute application traffic. Load balancers can enhance application performance by doing the following:
- Ensuring the efficient use of resources through the even distribution of requests across a group of application instances or servers.
- Preventing downtime by automatically redirecting requests to other instances or servers in the event that one application instance or server goes down.
- Supporting blue/green deployments where traffic switches automatically from an older application instance to a new one, enabling zero-downtime application upgrades.
Like reverse proxies, load balancers are typically "invisible" to clients. While it might appear that clients are sending requests directly to applications, in actuality, an internet-facing load balancer intercepts them using a public IP address assigned to the load balancing service. The load balancer then forwards the requests to the applications.
Reverse proxy vs. load balancer: Key features, advantages and limitations
Reverse proxies and load balancers can distribute or redirect incoming traffic between clients and the applications or servers they interact with. They can also provide basic traffic translation capabilities, such as Secure Sockets Layer termination, a process that decrypts traffic before passing it onto back-end servers.
Products advertised as reverse proxies often support load balancing features, so these services are not always mutually exclusive. For example, Nginx is an open source software tool offering both reverse proxy and load balancing capabilities. Products labeled strictly as load balancers generally do not provide features for inspecting, compressing, caching or enforcing security policies over requests.
As a result, in many cases, there are clear distinctions between reverse proxies and load balancers. The following categories highlight their varied capabilities along with potential tradeoffs.
Performance optimization
Reverse proxies can boost application performance through the compression or caching of request data. These capabilities reduce the amount of data moving over the network and, in turn, speed up request handling.
A basic load balancer's main performance-enhancing capability is its dynamic distribution of traffic across applications or servers to prevent request overload, which, if left unaddressed, would likely cause application performance degradation.
Security features
Most reverse proxies can block malicious requests and prevent the leakage of sensitive information by obfuscating the identity of back-end servers and encrypting data in transit.
Load balancer security capabilities are more limited by comparison, but they can mitigate distributed denial-of-service attacks by dropping high volumes of repeated requests.
Hardware vs. software deployment options
Reverse proxies are predominantly implemented through software.
Load balancers are available as both software-defined services and physical hardware devices. Software-based load balancers are typically more flexible and easier to deploy, especially in public cloud environments. Dedicated hardware load balancers have their own CPU and memory. They generally perform better in heavy workload environments, like data centers that process large traffic volumes, because they don't need to share resources with servers that host other services or workloads.
Cost and overhead
Costs can vary widely depending on how many requests a reverse proxy or load balancer processes and which types of actions it performs when managing traffic.
In general, load balancers cost less to deploy because their limited capabilities translate to lower resource consumption levels. Businesses likely won't need to pay for as much CPU and memory to support them.
When to use a reverse proxy vs. load balancer
A load balancer is often the most straightforward and cost-effective way to balance requests across a group of web applications or servers. Load balancers are especially appropriate for applications that include logic for tasks that identify and block malicious requests rather than relying on a proxy to handle those functions. Load balancers also work well in contexts where request volume is relatively low and caching or compression capabilities won't do much to improve performance.
For use cases that demand fine-grained control over request processing, a reverse proxy is a better option. This is also typically true for applications that experience low overall traffic volumes, as they don't require a load balancer's traffic optimization capabilities.
Chris Tozzi is a freelance writer, research adviser and professor of IT and society who has previously worked as a journalist and Linux systems administrator.
