Job Summary:
Proofpoint is a global leader in human- and agent-centric cybersecurity. They are seeking a Senior Proxy Engineer to design, build, and operate production-grade proxy infrastructure at scale, focusing on HTTP and related application-layer protocols while ensuring robust connection management and traffic shaping.
Responsibilities:
โข Architect and implement high-performance forward, reverse, and transparent proxy systems in Go with clean separation between the connection layer, protocol layer, routing layer, and upstream layer
โข Design proxy pipeline stages end-to-end: listener configuration, connection acceptance, TLS termination, protocol detection, virtual hosting, routing rule evaluation, request transformation, upstream selection, response streaming, and connection teardown
โข Build robust connection lifecycle management: keep-alive handling, half-close semantics, graceful shutdown, drain periods, and connection migration for rolling deployments
โข Implement traffic shaping primitives within the proxy: request hedging, retry budgets, timeout hierarchies (connect, first byte, total request), circuit breakers, and adaptive concurrency limits
โข Design and maintain upstream connection pools with configurable keep-alive timeouts, max idle connections per host, connection health checks, and zero-downtime upstream replacement
โข Own the header manipulation pipeline: request and response header rewriting, injection, removal, and normalisation with attention to correctness under HTTP/1.1 and HTTP/2 semantics
โข Architect multi-tenant proxy configurations with per-tenant routing policies, rate limits, authentication schemes, and traffic isolation guarantees HTTP Protocol Engineering & Standards Compliance
โข Maintain expert-level understanding of the core HTTP specification suite: RFC 9110 (HTTP Semantics), RFC 9112 (HTTP/1.1 Message Syntax), RFC 9113 (HTTP/2), RFC 9114 (HTTP/3), and RFC 9000 (QUIC)
โข Implement correct HTTP/1.1 connection management: persistent connections, keep-alive negotiation, chunked transfer encoding, request pipelining, and trailer fields Implement full HTTP/2 support: stream multiplexing, flow control (stream and connection level), header compression via HPACK, server push, RST_STREAM handling, and SETTINGS negotiation
โข Build HTTP/3 and QUIC proxying support: stream prioritisation, 0-RTT connection establishment, connection migration, and loss-recovery-aware flow control
โข Implement cache-control semantics per RFC 9111: Vary header handling, conditional request support (ETags, If-Modified-Since, If-None-Match), surrogate-key invalidation, and stale-while-revalidate
โข Handle HTTP edge cases defensively: malformed header detection, header field size limits, request smuggling mitigations (CL-TE and TE-CL desync), response splitting defences, and observer-invisible whitespace normalisation
โข Support WebSocket upgrade flows with correct Upgrade/Connection header handling, frame proxying, bidirectional streaming, and Ping/Pong keepalive management
โข Implement gRPC-over-HTTP/2 proxying: correct framing of length-prefixed messages, trailer handling for gRPC status codes, streaming RPC proxying, and gRPC-Web transcode
Qualifications:
Required:
โข Expert command of HTTP and related application-layer protocols
โข Deep experience architecting proxy systems
โข Primary development fluency in Go
โข Strong Lua scripting skills for runtime extensibility
โข Full lifecycle ownership of proxy platform including protocol-level design and connection management
โข Experience with TLS termination, request routing, traffic shaping, and upstream load balancing
โข Experience with forward proxies, reverse proxies, API gateways, and protocol translators
โข Familiarity with explicit HTTP proxying, transparent interception, SOCKS tunnelling, and CONNECT-based HTTPS proxying
โข Expert-level understanding of the core HTTP specification suite: RFC 9110, RFC 9112, RFC 9113, RFC 9114, and RFC 9000
โข Implementation of correct HTTP/1.1 connection management
โข Full HTTP/2 support implementation
โข Building HTTP/3 and QUIC proxying support
โข Implementation of cache-control semantics per RFC 9111
โข Defensive handling of HTTP edge cases
โข Support for WebSocket upgrade flows
โข Implementation of gRPC-over-HTTP/2 proxying
Preferred:
โข Familiarity with OpenTelemetry for deep proxy observability
Company:
Proofpoint provides cloud-based email security, e-discovery, and compliance solutions for companies to protect sensitive business data. Founded in 2002, the company is headquartered in Sunnyvale, USA, with a team of 1001-5000 employees. The company is currently Late Stage.