Understanding the Value of a Reverse Proxy Server

A reverse proxy server sits in front of your web and application servers and handles requests that arrive from endpoint devices and other servers on the network. Clients should never talk directly to application servers. Instead, they should talk to a reverse proxy server, which decides where each request needs to go, which security checks to run and how to return the response from the backend application server to request originators.

Using a reverse proxy control point changes what an infrastructure team can do with web application access requests. It makes applications easier to scale, gives security teams a place to apply policies and takes resource-intensive work, such as encryption, off application servers.

This article explains what a reverse proxy server does, how it differs from a standard proxy server, how a request flow works in practice and what to consider when deploying one.

What Is a Reverse Proxy Server?

A reverse proxy server acts as an intermediary between clients and the servers hosting your applications. It accepts inbound connections on behalf of those servers, forwards each request to the appropriate backend and returns the response to the client. In this scenario, a client can be another server — it doesn’t have to be an endpoint device that a person is using.

From the client’s perspective, the reverse proxy appears to be the web server. The browser resolves your public DNS name, connects to the proxy address and receives a response. It never learns the IP addresses, hostnames or the number of backend servers running the application.

That concealment matters, but additional value comes from what the proxy server can do while it mediates a connection. Because every request passes through it, the reverse proxy can distribute traffic across a server pool, terminate TLS/SSL, cache data, compress responses, authenticate users and inspect traffic for known attack patterns. A proxy platform can do what would otherwise require several separate tools.

In network terms, the reverse proxy usually sits at the edge of the application environment, behind the perimeter firewalls and in front of the web and application tier. Larger organizations often run one pair at the internet edge for public services and a second pair inside the data center for internal applications.

Proxy Server vs Reverse Proxy

People use the word proxy to describe servers managing network traffic flowing in both directions across the network and the web. This often causes most of the confusion around this topic. The difference comes down to which side of the conversation the proxy protects.

A proxy server, sometimes called a forward proxy, sits in front of clients. Users on a corporate network send their outbound requests to the proxy, which then fetches content from the internet on their behalf. Organizations typically deploy forward proxies to filter web access, enforce acceptable use policies, cache frequently accessed content and hide internal client addresses from external sites. This kind of proxy serves and protects users.

A reverse proxy sits in front of backend servers. It receives inbound requests from clients anywhere on the internet and distributes them across the backend infrastructure. Organizations deploy reverse proxies to hide and protect application servers, load-balance incoming traffic, offload encryption tasks and apply security policies. The reverse proxy works for the servers.

Table 1 shows the differences:

Both technologies terminate connections and forward traffic, so their underlying mechanics look similar. Their purposes rarely overlap. If you want to control what your staff can access, you need a forward proxy. If you want to protect and scale the services your customers access, you need a reverse proxy server. For a deeper look at how the two compare, read our guide forward proxy versus reverse proxy.

How Does a Reverse Proxy Work?

Requests from clients to a reverse proxy follow a consistent series of steps.

⁃ DNS resolution: A client looks up an application’s public hostname. The DNS service returns the address of the reverse proxy, not the address of any backend server hosting the application.

⁃ Connection and TLS handshake: The client opens a connection to the proxy. The proxy presents the site’s security certificate and completes a TLS (formerly SSL) handshake, creating an encrypted session that terminates at the proxy rather than at an application server.

⁃ Inspection and policy: The reverse proxy can now see the full request. It can check the request data and purpose against firewall rules, apply rate limits, compare the originating source address against reputation data and challenge for authentication credentials before passing the request to any backend servers.

⁃ Backend selection: The reverse proxy server (running on a load balancer) selects a server from the available server pool using an appropriate algorithm. Load balancers run background health checks and remove any server that stops responding properly from the available server list, so traffic reaches only instances capable of delivering a good user experience.

⁃ Persistence: If the application requires a user to stay on the same server for the duration of a session (or return to the same session after a dropped connection), the reverse proxy tracks that association using various methods such as cookies, the source address or other persistence methods.

⁃ Forwarding and response: The reverse proxy server forwards the request to the chosen backend application server, receives the responses and optionally caches, compresses and re-encrypts data before returning anything to the client.

Three items in those steps are particularly important. Let’s examine them in more detail.

TLS termination: Cryptographic certificate operations consume significant computing power. When a proxy handles the handshake and bulk encryption, application servers can focus their computing resources on delivering application logic. Certificate management also becomes a shared task rather than something each application server needs to handle. Organizations that need encryption all the way to the application backend can re-encrypt traffic on the internal leg between the proxy and backend servers, preserving the security-inspection benefits of reverse proxies without transmitting any unencrypted data.

Caching: A reverse proxy load balancer can store frequently requested data and serve it directly to clients on subsequent requests. Static assets such as images, stylesheets and scripts benefit most.

Compression: The proxy can compress data streams before sending them over the network, reducing bandwidth use and potentially shortening application load times for users on slower connections.

Where Organizations Deploy Reverse Proxies

Reverse proxy servers deliver the most benefit in front of specific types of applications. Typical examples are:

⁃ Public web applications: For example, a retailer running an e-commerce platform across several web servers should place reverse proxy servers in front of their application server pool, so the application survives a server failure and absorbs traffic peaks when you add servers behind the same public address and domain name.

⁃ Published enterprise applications: IT teams can publish services such as Microsoft Exchange, Microsoft SharePoint, remote desktop gateways and CMS platforms for internal use through a reverse proxy that can pre-authenticate users before any request reaches the applications. You can also do this in ways that honor zero-trust authentication principles if required.

⁃ Hybrid and multi-cloud estates: A reverse proxy provides a single entry point for services spanning on-premises servers and public cloud platforms. This flexibility lets you move application workloads to new hosting locations without changing public DNS records or firewall rules.

⁃ API and microservices traffic: Reverse proxies can route requests to the appropriate service based on the URL path or host header, allowing many different services to share a single hostname and certificate.

Benefits of Using a Reverse Proxy Server

Many benefits come from placing reverse proxy servers between backend servers and the clients that access them.

Reduced attack surface: Because backend servers sit behind proxy servers, they can use private addresses that don’t appear in public DNS records. Attackers scanning public address ranges typically find only the proxies, not the application servers, limiting the reconnaissance they can perform. This reduces the attack surface.

Application-layer security: A reverse proxy is the natural place to deploy a Web Application Firewall (WAF). Because the proxy decrypts traffic before forwarding it, the WAF can examine network packets and headers and apply rules that help detect and block common web attack methods. Rate limiting and IP reputation filtering at the same point help absorb volumetric and application-layer denial-of-service attempts before they reach application servers. Note that this rate limiting is not a substitute for upstream internet-based Distributed Denial of Service (DDoS) protection services. You still need those as part of a multi-layered cybersecurity and application resilience strategy.

Load balancing and scalability: The proxy servers distribute incoming requests across a server pool and route requests away from server instances that are overloaded and fail health checks. Adding capacity means adding servers to the pool, with no changes to public DNS or client configurations. This also makes patching and maintenance far less disruptive, since you can take one server offline at a time for maintenance while the others continue to function.

Centralized authentication: Pre-authentication at the proxies means users can prove their identity before application servers get requests. A reverse proxy that supports single sign-on and multi-factor authentication can also enable modern access controls for some legacy applications that will never implement modern authentication methods natively. This approach also aligns with zero-trust network access principles.

Better performance: Caching, data compression and connection reuse help reduce response times and lighten the load on application servers. Offloading TLS to the proxies also frees up processing capacity on the application servers for the core work they exist to do.

Simplified certificate management: Certificates live on the proxy rather than on every server in the pool. Renewals occur in one place, reducing the risk of an expired certificate taking a service offline. Plus, the Progress LoadMaster 360 solution can highlight upcoming certificate renewals and LoadMaster can use the ACME protocol to renew certificates automatically, to help prevent unplanned outages due to expired certificates. This will become more important as allowed certificate lifetimes are decreasing.

Why Reverse Proxies Matter More Than Ever

Modern applications span data centers, public and private clouds, plus edge computing solutions. Additionally, users can access services and applications from anywhere. A reverse proxy gives you one place to enforce policy across that spread, one place to scale and one place to apply application security controls.

If your current architecture exposes application servers directly, routes traffic through several disconnected tools or manages certificates server by server, a reverse proxy consolidates all of that into a single tier you can understand and manage more effectively.

Reverse Proxy Server Challenges

While reverse proxies offer many benefits, they also introduce challenges, as most technologies do. But the benefits outweigh these challenges:

Configuration complexity: Content-switching rules, persistence settings, health checks and security policies interact in ways that are not always obvious. Text-based configuration, in particular, rewards careful documentation and version control.

Latency and single points of failure: Every proxy adds a hop. A well-provisioned appliance adds very little latency, but an undersized instance or an inefficient rule chain shows up quickly in response times. Deploy proxies resiliently so a single failure is less likely to take an application offline.

Certificate lifecycle: Following on from the previous point, consolidating certificates on the proxy simplifies management but can also create a single point of failure if you don’t build resilience into the proxy servers.

Monitoring and logging: The proxy is a rich source of application traffic data and a place where a misconfiguration can remove servers from an application pool. Feed proxy logs into your existing monitoring platform and generate alerts on backend changes and proxy availability.

Reverse Proxy vs Load Balancer: What Is the Difference?

Many people ask what the difference is between a reverse proxy and a load balancer. The answer is that they are complementary technologies with many overlapping functions. Most modern products perform both roles, so the line between them has all but disappeared.

A load balancer distributes incoming traffic across multiple servers to prevent any single instance from becoming a bottleneck. That is its core function. A reverse proxy also distributes traffic and adds the broader set of capabilities described above, including TLS termination, caching, compression, authentication and content inspection.

Put simply, every reverse proxy that balances traffic functions as a load balancer, whereas a pure Layer 4 load balancer that forwards packets without terminating the session does not function as a reverse proxy. The Progress Kemp LoadMaster application delivery controllers combine both roles. They can operate at Layer 4 for raw throughput on protocols that need it, or use Layer 7 switching as a full reverse proxy for HTTP and HTTPS services that benefit from inspection and content-based routing.

In a typical deployment, you configure one virtual service as a Layer 7 reverse proxy for the web tier, with a WAF, pre-authentication and caching, and another as a Layer 4 balancer for a database or messaging protocol on the same instance.

How to Implement a Reverse Proxy Server

Here are some guidelines to follow when considering, choosing and deploying a reverse proxy server platform. The G2 Load Balancing Software Resources page is a useful starting point for comparing suppliers.

Choose the right software: The NGINX web server and Apache HTTP Server both offer reverse proxy modules and suit teams comfortable with text-based configuration files. The HAProxy load balancer delivers robust performance for high-volume Layer 4 and Layer 7 traffic. The LoadMaster solution takes a different approach, with a graphical management interface, PowerShell and API configuration options, application templates for common enterprise workloads and integrated security features that shorten deployment time for teams that don’t want to build a configuration.

Plan the configuration: Define the virtual services and public addresses you’ll use, add the real servers, then select a scheduling method and persistence mode that match how the application handles sessions. Configure health checks that test the application itself rather than a server port, because an active port doesn't indicate whether an application can respond to a request.

Apply security controls in layers: Install certificates and set a modern TLS policy, then decide whether connections from the proxy to backend servers stay in plain text or carry a fresh TLS session. Turn on the WAF in detection mode first, review what it flags against real traffic, then move to blocking once you have tuned out false positives. Add pre-authentication for any application that supports it.

Test and monitor: Validate failover by taking a backend server out of service during a controlled window. Load test through the proxy rather than around it. Then connect the proxy to your monitoring stack so you can see traffic patterns, backend server health and certificate expiry issues in the same place as the rest of your infrastructure.

Try the LoadMaster Solution for Yourself

The G2 Grid® Report for Load Balancing reviews show that the LoadMaster platform stands out as an industry favorite among load balancing solutions for businesses of all sizes.

It is also ideal for departments within larger organizations that need a load balancer for development, DevSecOps or even non-revenue-generating production deployments. Check out our Free Load Balancer option for small or non-commercial use cases.

Nearly all LoadMaster versions align with modern deployment needs, provide comprehensive functionality and offer flexible licensing, including industry-leading subscription options, resulting in a lower cost of ownership than other vendors’ offerings. https://community.progress.com/s/products/loadmasterAdd our industry-leading support, and you will soon understand why G2 ratings for the LoadMaster solution stay consistently excellent.

Download a free 30-day trial version today (free registration required) or request a live demo from our expert team.

Reverse Proxy Server FAQs

How is a reverse proxy different from a forward proxy?

A forward proxy sits in front of clients and manages their outbound requests to the internet. A reverse proxy sits in front of servers and manages inbound requests from clients. One helps protect users, while the other helps protect applications.

When should I use a reverse proxy server?

Use a reverse proxy server whenever you publish an application to users outside its network segment, run an application across multiple servers, need to apply security controls to traffic before it reaches an application or want to consolidate certificate management.

Which software can I use to set up a reverse proxy?

NGINX, Apache HTTP Server and HAProxy all provide reverse proxy functionality. Application delivery controllers, such as the LoadMaster ADC, combine reverse proxy, load balancing, WAF and authentication features into a single platform with multiple management options.

Can a reverse proxy improve website performance?

Yes. Caching reduces redundant requests to the backend. Compression reduces the volume of data sent to clients, and TLS offloading frees up processing capacity on application servers. Load balancing across a pool also helps prevent any single server from becoming a bottleneck.