What is the role of TLS/SSL Offloading in Proxy Servers and Load Balancers? Bridging vs Termination vs Passthrough

In the realm of web architecture, two essential players come into focus: reverse proxy servers and load balancers.

Let’s start with reverse proxy servers. Imagine them as intermediaries between users and servers. They act as gatekeepers, receiving requests from users and forwarding them to the appropriate servers that can fulfill those requests. This setup offers a layer of security by shielding the backend servers from direct exposure to the internet.

Load balancers focus on distributing incoming traffic across a group of servers. They work to prevent any single server from being overwhelmed, thereby improving performance and ensuring that the system remains responsive. By evenly distributing the workload, load balancers optimize resource utilization.

Within the framework of reverse proxies and load balancers, TLS/SSL encryption serves as a vital security mechanism that protects the privacy and authenticity of data exchanged between clients and servers. TLS/SSL encryption guarantees that sensitive information remains confidential as these intermediaries efficiently route traffic to backend servers.

What is TLS/SSL?

Transport Layer Security (TLS) and Secure Sockets Layer (SSL) are protocols designed to enhance the security of communication between two systems.

They achieve this by encrypting the data exchanged and providing authentication to ensure that the other party is genuine. While both TLS and SSL share the goal of securing information transfer, TLS has largely replaced SSL due to its advancements and strengthened security features.

TLS not only builds upon SSL’s foundation of encryption and authentication but also introduces improved cryptographic algorithms, flexible cipher suite negotiation, enhanced alert mechanisms, and better protection against vulnerabilities.

In TLS, each message is encapsulated in a record that includes a header and an encrypted payload. The Message Authentication Code (MAC) is a crucial component embedded within this encrypted payload. It’s computed using a combination of the message content, a unique sequence number, and a secret key.

The MAC is encrypted alongside the message, which means someone trying to alter the payload would entail modifying the data, aligning the MAC accordingly, and circumventing the established security protocols. This makes it very difficult to tamper with packets.

By verifying the MAC upon decryption, the recipient can ensure the message’s authenticity and integrity. The use of sequence numbers and padding ensures consistent block sizes and helps protect connections against certain attacks.

HTTPS Traffic Flow

When you connect to a secure website using “https://”, your web browser and the website’s server engage in a secure handshake powered by TLS/SSL. The handshake begins with your browser and the server agreeing on encryption methods and exchanging keys for securing communication.

The server then presents its digital certificate, essentially an ID card, proving its authenticity.

Your web browser confirms the legitimacy of the server by checking its digital certificate against trusted authorities, ensuring that the server is genuine. With the server’s authenticity established, both your browser and the server agree upon a secret encryption key. Utilizing this key, your browser and the server encrypt the data before transmission.

As data travels between you and the server, your browser checks if the data maintains the correct encryption seal and hasn’t been tampered with during transit, thanks to TLS/SSL.

However, the burden of HTTPS decryption on a proxy server warrants attention. The decryption process, aimed at inspecting or manipulating HTTPS traffic, introduces a computational overhead that has the potential to strain server resources. Such strain can hamper server performance and responsiveness, particularly during periods of intense traffic load.

TLS/SSL Traffic Handling

There are three prominent methods of handling TLS/SSL traffic: termination, bridging, and passthrough. These techniques play a pivotal role in ensuring encrypted communication remains efficient, secure, and aligned with specific operational needs.

While these methods are primarily associated with load balancers and reverse proxy servers, their application in forward proxy setups is relatively uncommon. Forward proxies engage in routing client requests to external servers, with a focus on outgoing traffic. However, certain scenarios might warrant the utilization of these TLS/SSL handling techniques in forward proxies, especially when outgoing traffic demands inspection or security filtering.

TLS/SSL Termination relieves backend servers from the resource-intensive decryption process by passing this responsibility to the load balancer or proxy server. This method is primarily employed as a performance optimization technique improving overall server responsiveness.

In TLS/SSL Bridging, the load balancer intercepts and decrypts client traffic, then re-encrypts it before forwarding it to backend servers. This approach strengthens security measures by enabling inspection and potential modifications to be carried out before the traffic enters the internal server environment.

TLS/SSL Passthrough maintains end-to-end encryption by directly forwarding encrypted client traffic to backend servers without decryption. This approach ensures data confidentiality but limits the load balancer’s visibility and control over the encrypted content. This method is advantageous in scenarios where privacy and direct communication between clients and servers are prioritized.

SSL Termination and SSL Bridging both centralize SSL certificate management, handled by the load balancer or proxy server. In contrast, SSL Passthrough leaves SSL certificate management to individual backend servers.

TLS/SSL Termination

Imagine this: a client connects to a website through a secure and encrypted HTTPS link. This encrypted connection then takes a detour through a load balancer/proxy server, which has an unencrypted HTTP link with the destination server.

While the link between the user and the proxy server maintains its encryption through HTTPS, you might be curious about the path the data follows to reach the destination server. On this path, the data remains unencrypted as it travels from the proxy server to the destination server using the HTTP protocol.

The question naturally arises: does this transition between encryption and decryption compromise security? To maintain the core benefits of SSL/TLS Termination, it’s generally recommended to keep the proxy server within the same network as the backend servers. This way the HTTP connection is protected by the internal network firewalls. However, if the proxy server is on an external network it requires careful planning to both establish an encrypted connection and ensure that performance benefits of SSL/TLS Termination are not compromised.

TLS/SSL Termination serves to boost server performance and simplifying the handling of encrypted traffic. By managing the decryption process, SSL Termination lightens the workload on backend servers. This leads to faster loading times and more responsive websites. TLS/SSL Termination is particularly valuable for websites that focus on sharing content, like blogs and informative platforms that deal with non-sensitive user data.

TLS/SSL Bridging

In the TLS/SSL Bridging process, a load balancer or proxy server, takes on the role of handling the incoming encrypted connection, decrypting the data, and then establishing a fresh, encrypted connection with the backend server. This approach provides several benefits in terms of both security management and performance optimization.

In contrast to TLS/SSL Termination, where decrypted data travels unencrypted on an internal network, TLS/SSL Bridging maintains encryption throughout the process. The decrypted data is never exposed on an internal network; instead, it is encrypted again before being forwarded to the backend server. This dual encryption and decryption process maintains the confidentiality of the data even during the transition between the load balancer and the backend server.

Bridging allows the load balancer or proxy server to inspect the decrypted content of the encrypted traffic before it’s forwarded to the backend server. This inspection can involve checking for malicious content, performing content filtering, or applying security policies.

Imagine a financial institution with a widespread network of branches requires secure and efficient communication between its customers and its online banking platform.To ensure both data privacy and optimal performance, the institution implements TLS/SSL Bridging. By employing load balancers that terminate encrypted connections, decrypt data, and then establish encrypted links with backend servers, the institution achieves optimal decryption, increases security, and reduces the strain on its servers.

TLS/SSL Passthrough

In TLS/SSL Passthrough the encryption and decryption process takes place exclusively between the client and the server. The proxy server to simply relay the encrypted traffic without intervening in the encryption layer. This means that the application server itself handles the decryption of incoming traffic and the encryption of outgoing traffic.

TLS/SSL Passthrough is particularly useful in scenarios where the application’s security and encryption requirements demand direct communication between the client and the application server without any intermediaries having access to the decrypted data. This method is often employed in industries like finance, healthcare, and e-commerce, where strict compliance regulations mandate that data remain confidential throughout its journey.


It’s clear that proxy servers bring a lot to the table when it comes to boosting network performance and tightening security. And with the help of TLS/SSL offloading techniques like Termination and Bridging, those computational hurdles tied to encrypted traffic can be avoided. So, whether you’re an individual after some privacy perks or a business trying to keep things running smoothly, diving into the world of proxy servers and TLS/SSL traffic handling can really pay off.