Apache Traffic Server vs Varnish: What are the differences?

Introduction

Apache Traffic Server and Varnish are both popular open-source web caching solutions used to improve the performance and scalability of websites. While they serve the same purpose, there are several key differences between the two.

1. Architecture and Configuration:

   • Apache Traffic Server (ATS) follows a proxy-based architecture where it acts as an intermediary between clients and servers. It requires custom configuration for features like caching, SSL termination, and load balancing.
   • Varnish, on the other hand, is designed as a reverse proxy cache. It operates by sitting in front of web servers and caches content based on a set of predefined rules. Its configuration language, VCL (Varnish Configuration Language), allows fine-grained control over cache handling and response modification.

2. HTTP/2 Support:

   • Apache Traffic Server supports HTTP/2, the latest HTTP protocol version. It can handle both HTTP/1.x and HTTP/2 traffic efficiently.
   • Varnish, as of now, only supports HTTP/1.x. It doesn't have built-in support for HTTP/2, which may limit its performance in websites utilizing this newer protocol.

3. Plugins and Modules:

   • Apache Traffic Server offers a wide range of plugins and modules for additional functionality. It has a flexible plugin architecture that allows customization and integration with third-party tools and services.
   • Varnish also provides various modules to extend its capabilities, but the available options are relatively limited compared to ATS. However, Varnish excels in its ability to customize cache handling through VCL.

4. Ecosystem and Community Support:

   • Apache Traffic Server has an extensive community with active development and regular updates. It is supported by the Apache Software Foundation and has a mature ecosystem with comprehensive documentation.
   • Varnish also benefits from a strong community but is not backed by a large organization like Apache. However, it has gained popularity and support from organizations that use it extensively in their infrastructure.

5. Hardware Requirements:

   • Apache Traffic Server is known to require more resources, both in terms of CPU and memory, compared to Varnish. Large-scale deployments of ATS may require more powerful hardware to handle the traffic efficiently.
   • Varnish is designed to be lightweight and highly efficient in terms of resource consumption. It can handle significant traffic loads with minimal hardware requirements, making it a suitable choice for smaller or resource-constrained environments.

6. TLS Termination and SSL Support:

   • Apache Traffic Server provides built-in support for TLS termination, allowing it to handle SSL encryption and decryption. It simplifies the setup process and offloads the SSL processing from backend servers.
   • Varnish, by default, does not have native support for SSL termination. It requires additional tools or setups (like HAProxy) before SSL traffic can be handled. This adds an extra layer of complexity in the configuration and deployment process.

In summary, Apache Traffic Server and Varnish differ in their architecture, HTTP/2 support, plugin/modules availability, community support, hardware requirements, and SSL handling capabilities. Choosing between the two depends on specific requirements, scalability needs, and the desired level of customization.