Lessons Learnt Migrating CDN apps for WebAssembly

Kit Chan - Yahoo

For years Yahoo owned & operated its own Content Delivery Network(CDN). It built upon Apache Traffic Server and features a plugin architecture that facilitates the development of C++ modules. These modules provide unified functionality across all Yahoo properties, such as cookie management, privacy control, & web application firewall.

In recent years, there has been an initiative to transition our infrastructure & workloads to leverage third-party platform vendors. CDN is no exception. The biggest hurdle is to migrate the aforementioned functionality, provided by a legacy C++ codebase built over a long period of time, to a new vendor

In this presentation we will show how WebAssembly can help save the day. We will examine the WebAssembly support from a number of CDN vendors and open source proxy servers. We will then detail the process of adapting our codebase for the WebAssembly platforms provided by these options & share a few interesting lessons learnt along our journey. We want to share our experiences with various compilation toolchains and WebAssembly runtimes. We have to make adjustments to organization of the codebase to accommodate various team working together on the platform. We encountered and solved interesting static compile time issues as well as unexpected surprising dynamic runtime issues. There are also challenges in vendor lock-in, performance, debugging, testing and observability that we have to overcome to make our project successful.