Layer 7 load balancing: The complete guide to boosting application performance

For many of you, Layer 7 will become your go-to load balancing method. It's become more and more popular for web applications because of its powerful features and the complex way modern internet traffic works.

In this guide, I'll walk you through everything you need to know about Layer 7 load balancing, from understanding what it is to finally getting it configured.

Table of contents

• What is Layer 7 load balancing?
• Is Layer 7 the same thing as reverse proxy?
• Layer 7 load balancing protocols
• How Layer 7 load balancing works
• Benefits of Layer 7 load balancing
• Common Layer 7 use cases
• How to configure Layer 7 load balancing
• Using Layer 7 and GSLB in tandem

What is Layer 7 load balancing

Understanding Layer 7 application load balancing

Layer 7 load balancing intelligently routes traffic at the Application Layer of the OSI (Open Systems Interconnection) model, examining the content being delivered, and routing it accordingly.

It is the most flexible method of load balancing, providing high availability and scale for applications, while being easy to implement.

Other names for Layer 7 load balancing include Application Layer load balancing, and HTTP Load balancing.

What’s the difference between Layer 7 and Layer 4 load balancing?

Layer 7 load balancers are content aware, whereas Layer 4 load balancers operate at the Transport Layer of the OSI model, forwarding traffic without inspecting its contents.

For more on the different load balancing methods check out this blog: Compare Layer 4, Layer 7, and GSLB.

What’s the difference between an API gateway and a Layer 7 load balancer?

While a Layer 7 load balancer and an API gateway both manage and route traffic at the Application Layer, they have distinct feature sets and serve different purposes.

A Layer 7 load balancer distributes network traffic efficiently across a group of backend servers to optimize performance and ensure high availability. An API gateway is a dedicated management tool for API requests. While it can include L7 load balancing capabilities as a feature, its core purpose is to act as a single point of entry for all API calls.

Is Layer 7 the same thing as reverse proxy?

Layer 7 load balancing is NOT the same thing as Reverse Proxy but they are very closely related!

A reverse proxy is a general type of server that handles incoming requests and sends them to the right web server.

A Layer 7 load balancer is a more specialized kind of reverse proxy. Its key job is to distribute traffic across a group of servers to ensure high performance and availability.

So, think of a Layer 7 load balancer as an upgraded, more intelligent version of a reverse proxy, designed specifically to manage heavy traffic.

What is a reverse proxy?

A reverse proxy is what handles all incoming requests before they ever reach your servers. It acts as an intermediary, receiving a request from a user and then forwarding it to one of your backend servers.

Reverse proxy acts as a helpful middleman, and that comes with a lot of perks. It can give you:

• Better security: It hides your actual servers from the outside world, keeping them safe from direct attacks.
• SSL/TLS termination: It handles all the heavy lifting of encrypting and decrypting traffic, freeing up your servers to focus on their main job.
• Faster performance: It can cache static files like images and CSS, which means less work for your servers and quicker load times for your users.
• URL rewriting: It can change the URL of a request before it even gets to your servers, giving you more control over your traffic flow.

What is a Layer 7 load balancer?

A Layer 7 load balancer works at the Application Layer of the OSI model, which is a fancy way of saying it reads the actual content of a request. It can examine things like the URL, HTTP headers, or even a cookie to make a smart decision about where to send the traffic.

For example, it can send an image request to a server that's great at serving static files. At the same time, it can route a request to a user's shopping cart to a completely different server that handles that kind of work.

Because it's reading the request's content, a Layer 7 load balancer is naturally a specific type of reverse proxy. It receives and forwards requests, but with the added responsibility of distributing traffic based on application-level logic.

So, while a Layer 7 load balancer is a reverse proxy, the reverse isn't always true. Not all reverse proxies are Layer 7 load balancers. A reverse proxy can be a simple intermediary for a single server or could be configured for tasks like SSL termination or caching without ever needing to distribute traffic across multiple servers.

Layer 7 load balancing protocols

Layer 7 load balancing operates at the application layer of the OSI model, using the HTTP protocol.

This is the protocol that gets web pages and other content from a server to your browser. HTTPS is just the secure, encrypted version.

For more on HTTP, check out our beginner's guide:

How Layer 7 load balancing works

Layer 7 load balancing uses a proxy at the application layer. Inbound requests are terminated on the load balancer and HAProxy generates a new corresponding request to the chosen Real Server. As a result, Layer 7 is typically not as fast as the Layer 4 methods. Layer 7 is typically chosen when either enhanced options such as SSL termination, cookie based persistence, URL rewriting, header insertion/deletion etc. are required, or when the network topology prohibits the use of the Layer 4 methods.

The image below shows how Layer 7 load balancing works:

Since Layer 7 load balancing acts as a full proxy, your backend servers can be located anywhere on the network—even across the internet or a WAN.

By default, Layer 7 load balancing isn't transparent. This means your servers won't see the client's real IP address. Instead, they'll see the load balancer's IP address (or another local appliance's IP, if you've set it up that way).

You can actually change this setting for each Layer 7 VIP. If you need to, the load balancer can be configured to send the real client's IP address to your servers in one of two ways. It can either:

• Add a new header with the client's IP address inside.
• Or, it can change the IP address of the traffic itself, replacing its own address with the client's.

Benefits of Layer 7 load balancing

Layer 7 load balancing can improve application performance in the following ways:

Intelligent routing

Layer 7 load balancing is smart because it looks at the actual content of a request—things like the URL, headers, or even cookies. This lets it make intelligent decisions about where to send traffic.

For instance, it can send requests for images and CSS files to one set of servers, while directing API calls to a completely different group. This level of control ensures every request goes to the best possible server, which makes everything run more efficiently and gives the user a better experience.

Improved performance

Layer 7 load balancing boosts your app's performance in a couple of ways, for example through SSL offloading and caching.

It handles the demanding job of encrypting and decrypting traffic, which frees up your web servers to focus on their main tasks.

This whole process makes it much easier to scale your application, as you can add or remove servers from the pool without affecting the system's performance.

Enhanced security

Because it inspects the application layer, a Layer 7 load balancer can provide powerful security features that aren't possible at other levels.

It acts as a full proxy, shielding your backend servers from direct exposure to the internet. This lets it handle the heavy lifting of SSL/TLS termination, which decrypts and encrypts traffic before it ever reaches your servers. It can also filter out malicious requests, block common attacks, and prevent direct exploits.

Common Layer 7 use cases

I would definitely recommend considering Layer 7 load balancing when you want to implement any of the following:

1.Content switching

Because Layer 7 load balancing is content-aware, this allows for:

• URL-based routing: A Layer 7 load balancer can look at the URL to send traffic to the right place. For example, it can send requests for /images to servers that are great at handling static content, while sending API requests to a different group of servers.
• Cookie-based persistence: This is a huge benefit for keeping a user's session consistent. The load balancer can use a cookie to make sure a user's requests always go to the same server, which is essential for things like shopping carts where the session state is stored on a specific server.
• Device-specific routing: It can send traffic from mobile devices to servers optimized for mobile apps, while routing desktop traffic to your main web application servers. This helps ensure everyone gets a smooth experience no matter what device they're on.

2.Security and protocol handling

Layer 7 load balancing can also provide a security buffer e.g.

• Acts as a full proxy: A Layer 7 load balancer acts like a shield. It ends the connection from the client and creates a new one to the backend server. This hides your servers from the internet, so attackers can't target them directly. All threats are handled by the load balancer first.
• SSL/TLS termination: In this scenario the load balancer handles all the heavy lifting of encrypting and decrypting traffic. This not only frees up your web servers to focus on their main jobs but also allows the load balancer to inspect the content for threats before it's sent to your application.
• Content and header filtering with WAF: A Layer 7 load balancer with a Web Application Firewall can be configured to filter traffic based on a set of specific rules you create. For instance, you can use a Core Rules Set (CRS), which is a collection of pre-made rules that can detect and block known malicious content, like SQL injection attacks or suspicious headers. This gives your application an extra layer of defense against common threats.

3.Performance optimization

Layer 7 load balancing can also be used to accelerate application performance.

For example, the load balancer can compress responses before sending them to the client. This reduces the amount of data that needs to be transferred, which in turn helps your web pages load faster.

In high-traffic situations, the load balancer can also prioritize certain kinds of requests. For example, it can make sure that API calls are handled before requests for less important content, ensuring a smooth and consistent experience for your users.

How to configure Layer 7 load balancing

The configuration steps will vary depending on the mode used and the application being load balanced, but here are some example use cases with step-by-step configuration and deployment instructions.

How to configure Layer 7 load balancing

Here are some example applications that could benefit from Layer 7 load balancing and individual guides to explain how to configure the load balancer in each scenario:

• How to load balance AGFA Healthcare Enterprise Imaging with Layer 7
• How to load balance Boomi Blueprint with Layer 7
• How to load balance Ceph Object Gateways with Layer 7
• How to load balance Citrix StoreFront with Layer 7
• How to load balance Cloudian HyperFile with Layer 7
• How to load balance Cribl Stream with Layer 7
• How to load balance CTERA Portal with Layer 7
• How to load balance Ellucian Banner with Layer 7
• How to load balance EMIS Symphony with Layer 7
• How to load balance Epicor ERP 10 with Layer 7
• How to load balance Epicor Kinetic ERP 11 with Layer 7
• How to load balance Hitachi Content Platform with Layer 7
• How to load balance HPE Ezmeral with Layer 7
• How to load balance Huawei OceanStor with Layer 7
• How to load balance Hyland OnBase with Layer 7
• How to load balance Konica Minolta Dispatcher with Layer 7
• How to load balance Mach7 Technologies with Layer 7
• How to load balance Meditech RESTful API with Layer 7
• How to load balance Microsoft Remote Desktop Services with Layer 7
• How to load balance Microsoft SQL Server with Layer 7
• How to load balance Nutanix Object Storage with Layer 7
• How to load balance Oracle PeopleSoft with Layer 7
• How to load balance Oracle JD Edwards EnterpriseOne with Layer 7
• How to load balance Panzura CloudFS with Layer 7
• How to load balance Powerschool eSchoolPlus SIS with Layer 7
• How to load balance RedHat OpenShift with Layer 7
• How to load balance RedHat OpenStack with Layer 7
• How to load balance SMTP Servers with Layer 7
• How to load balance Storage Made Easy File Fabric with Layer 7
• How to load balance YSoft SafeQ with Layer 7

Using Layer 7 and GSLB in tandem

Layer 7 load balancing is often used in combination with GSLB to create multi-site resilience.

Global Server Load Balancing (GSLB) provides traffic distribution across server resources located in multiple locations, for example, multiple data centers or a single disaster recovery (DR) site for redundancy. It passes the traffic straight to the load balancer which does more granular balancing and health checking.

GSLB active-active load balancing example:

Demand for GSLB has grown significantly in the last three years, as large numbers of organizations have migrated away from traditional on-premise systems and have instead created hybrid cloud and hosted environments. Many have also made the strategic decision to split their data resources across multiple locations to improve business resilience and reduce costs.

What are the pros of GSLB for multi-site resilience?

• Flexible health checks to ensure application uptime.
• Topology based routing ensures that internal traffic uses the local data center, avoiding the cost and performance issues of over-using WAN links.
• It can detect users’ locations and automatically route their traffic to the best available server in the nearest data center.

What are the cons of GSLB for multi-site resilience?

• Sometimes applications do not support DNS and therefore can’t failover using GSLB (we do however have a solution for that).

Conclusion

Layer 7 load balancing has become a crucial tool for modern applications, offering a powerful way to manage complex internet traffic.

By inspecting the content of requests, it provides intelligent routing, enhanced security, and improved performance through features like SSL offloading and caching. As this guide has shown, Layer 7 load balancing is a highly specialized type of reverse proxy, acting as an advanced traffic manager that can optimize your entire application stack. It's also often used in tandem with Global Server Load Balancing (GSLB) for multi-site resilience, creating a robust and highly available architecture. As the web continues to evolve, so too will the load balancers that power it, ensuring applications remain fast, secure, and resilient.

If you’re thinking of implementing Layer 7 and need to establish a Proof of Concept, feel free to reach out for a free consultation with one of our technical experts.

More on other load balancing methods

• Layer 4 load balancing guide
• When and how to use Global Server Load Balancing (GSLB)
• Compare Layer 4, 7, and GSLB techniques