Senior Engineer - VCL Compiler

Fastly•San Francisco, NY

2d•Hybrid

About The Position

Fastly helps people stay better connected with the things they love. Fastly’s edge cloud platform enables customers to create great digital experiences quickly, securely, and reliably by processing, serving, and securing our customers’ applications as close to their end-users as possible — at the edge of the Internet. The platform is designed to take advantage of the modern internet, to be programmable, and to support agile software development. Fastly’s customers include many of the world’s prominent companies, including GitHub, Yelp, Paramount, and JetBlue. We're building a more trustworthy Internet. Come join us. Sr Software Engineer, VCL Compiler We are looking for a Compiler Engineer to join our Core Platform team to help shape, scale, and maintain the VCL Compiler (VCC) and Varnish Configuration Language (VCL). VCL is at the heart of how our customers configure and customize their edge logic at scale. In this role, you will be responsible for evolving the language design, refactoring compiler architecture, and ensuring the absolute stability of a codebase that processes billions of requests per second. You will balance building innovative language features with the meticulous, detail-oriented work of maintaining backward compatibility, writing robust test suites, and optimizing our C-based code generation pipeline.

Requirements

Significant domain-relevant engineering experience - Most Senior Engineers at Fastly have at least 5 years of related experience.
Significant production experience writing C, with knowledge of POSIX/Linux environments
Solid understanding of compiler internals: parsing, AST design, intermediate representations, code generation
Experience simplifying and refactoring established codebases while maintaining backward compatibility
Track record of comprehensive testing practices, CI/CD, and treating the build pipeline as production infrastructure
Good written communication skills, with the ability to produce clear technical documentation
A collaborative mindset with experience working across cross-functional teams

Nice To Haves

Previous Fastly engineering experience
Contributions to open source compiler or language projects
Familiarity with Varnish, VCL, or CDN/edge computing infrastructure
Background in domain-specific language (DSL) design

Responsibilities

Design and implement VCL language extensions, syntax updates, and new compiler features
Parsing and AST rework to improve long-term maintainability of the compiler
Refactor and modularize the existing compiler codebase to reduce complexity and improve stability
Own the testing and validation pipeline to ensure compiler changes don't break existing customer code
Collaborate with cross-functional teams to align on architecture and technical direction
Write clear technical documentation for internal teams and external users