Difference Between Layer 4 vs. Layer 7 Load Balancing

Harish R
3 min readAug 30, 2021


A load balancer is an essential component of server’s health monitoring. It is a logical device that acts as a traffic controller, by distributing network or application traffic among multiple servers. Load balancers are commonly used to improve application capacity and dependability. Without load balancers, it is very likely that an application’s or site’s servers may fail more frequently than they should, causing operations to be disrupted.

Load balancers increase application performance by reducing the load on servers that manage and maintain application and network sessions, as well as those that execute application-specific activities.

Load balancers functions are frequently divided into two categories: Layer 4 and Layer 7 as pe the OSI Model. Here are the advantages and disadvantages of each to help you decide which one would be ideal for your use case:

Layer 4 (Transport Layer) Load Balancer

Layer 4 load balancing takes place at the transport layer of the OSI model, which is in charge of delivering messages regardless of their content. Layer 4 load balancers simply route network packets to and from the upstream server without inspecting them. By reviewing the initial few packets in the transmission control protocol (TCP) stream, they can only make limited routing decisions. It is still the heart of the OSI.

The advantages of Layer 4 Load Balancing

Suitable for packet-level balancing of loads

It is quick and efficient because it does not take data into account.

Because packets are not examined, they are more secure. If it is compromised, no one will be able to access the data.

It just forwards the packets. It does not need to decrypt the content before forwarding.

NAT is used.

Maintains only one NATed connection between the client and the server, allowing your load balancer to serve a maximum number of TCP connections.

The disadvantages of Layer 4 Load Balancing

Based on the content, smart load balancing is not possible.

Cannot perform true microservices.

Because it is a stateful protocol, it must be sticky. When a connection is established, it is routed to a single server in the backend. All packets sent through this connection are routed to a single server. Based on the algorithm, the next connection will select another server.

Layer 7 (Application Layer) Load Balancer

Layer 7 load balancing works at the application layer of the OSI model, which is in charge of the message’s actual content. Application Load Balancers route network traffic in a more complex way, typically for TCP-based traffic such as HTTP or HTTPS. A Layer 7 load balancer, unlike a Layer 4 load balancer, disconnects network traffic and processes the message inside.

It makes the call depending on the message’s content. Once decided , it establishes a new TCP connection to the designated upstream server and sends the request to the server. Layer 4 is not capable of caching because it has no idea what is in the packets.

The advantages of Layer 7 Load Balancing

Based on the URL, it provides smart routing.

It offers caching.

The disadvantages of Layer 7 Load Balancing

It is expensive.

Decryption is required.

In terms of security, your certificate must be shared with the load balancers. If an attacker gains control to the load balancer, they will have total access to all of your data.

Its proxy establishes several connections — client to proxy/proxy to server — so you are limited by the load balancer’s maximum TCP connection.


When it comes down to it, the decision to use Layer 4 and Layer 7 load balancing is based on your specific requirements. When deciding on the ideal load balancer for your applications, it’s a good idea to talk with an expert because they’ll keep your apps or servers safe and secure while maximising uptime.



Harish R

DevOps and Cloud Engineer, Blogger — Personal Finance, Money Entrepreneurship and Life Advice.