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Capabilities & Limitations

A one-screen, legend-coded map of what ExpressGateway supports, what is gated off, what is waived, and what is deferred. Every row points at the page that owns the detail — this page is the index, not the explanation.

  • The bounded why behind every gated/waived/deferred item lives in ../known-limitations.md (with a "who does this affect?" note on each).
  • The protocol matrix and feature detail live in ../features.md.
  • Every config knob and its reload class live in CONFIG.md.
  • The threat model and audit posture live in ../../SECURITY.md.

Legend: ✅ supported · ⛔ gated off by default · ☑️ opt-in · ⚠️ bounded limitation · ⏳ deferred / not yet characterized.

HTTP protocol matrix (front × back)

The full 9-cell matrix — any of {H1, H2, H3} on the client side translated to any of {H1, H2, H3} on the backend — streamed frame-by-frame with bounded memory (64 MiB caps + 413). Front protocol is the listener protocol; back protocol is the per-backend protocol. H2 is served on an h1s listener via ALPN; H3 on a quic listener. Detail: ../features.md.

front ↓ \ back → H1 H2 H3
H1 ✅ ✅ ✅
H2 ✅ ✅ ✅
H3 ✅ ✅ ✅

QUIC modes

Mode Status Detail
H3 terminate (default for quic) ✅ ../features.md
Mode A passthrough ([passthrough]) — route by Connection ID, no decrypt ✅ ⚠️ ../known-limitations.md
Mode B terminate ([listeners.quic.raw_proxy]) — re-originate upstream QUIC ✅ ../features.md

Application protocols

Feature Status Detail
HTTP/1.1, HTTP/2, HTTP/3 ✅ ../features.md
gRPC (needs an H2/H3 front + h2/h3 backend) ✅ ⚠️ ../known-limitations.md
WebSocket over H1 (RFC 6455) ✅ ../features.md
WebSocket over H2 (RFC 8441) ⛔ ../known-limitations.md
WebSocket over H3 (RFC 9220) ☑️ ../features.md
Response compression ❌ pass-through only (incumbents have it) — comparison.md

Load balancing & health

Aspect Status Detail
Round-robin (L7 HTTP + raw-TCP) ✅ live selection policy in this build — ../features.md "Load balancing"
Maglev by Connection ID (QUIC Mode A) ✅ passthrough flow routing — ../features.md
Other algorithms (weighted RR, P2C, ring-hash, EWMA, least-conn, least-request, random, weighted-random, session-affinity, Maglev-for-L7) ⏳ implemented in lb-balancer but not yet selectable from config — ../features.md
Per-backend weight ⏳ parsed but not enforced in this build (round-robin ignores it) — CONFIG.md
Passive health tracking ⏳ implemented but not yet wired into selection — ../known-limitations.md
Active health probing (interval/path/expected-status) ⏳ deferred — ../known-limitations.md

TLS

Aspect Status Detail
Stack (rustls + BoringSSL) ✅ ../features.md
TLS 1.2 + 1.3 (downgrade-safe); tls13_only opt-in ✅ ☑️ ../features.md
Server-side mTLS ⚠️ not provided (intentional) ../known-limitations.md
Upstream certificate verification ✅ enforced ../../SECURITY.md

Conformance

Suite Status Detail
h2spec (HTTP/2) ✅ 147/147 ../features.md
h3spec (HTTP/3 + QUIC) ⚠️ passes with 12 named waivers ../known-limitations.md

L4 / XDP data plane

Aspect Status Detail
XDP/eBPF TCP+UDP fast path ✅ ⚠️ off by default ([runtime].xdp_enabled) DEPLOYMENT.md
Kernel portability ⚠️ single-kernel (not CO-RE-portable) ../known-limitations.md
ENA native (xdpdrv) attach ⚠️ MTU ≤ 3498 + reduced channels DEPLOYMENT.md

With XDP off (the default), L4 traffic uses the kernel TCP/UDP stack normally with no loss.

Operations

Feature Status Detail
SIGHUP config hot reload (swappable subset) ✅ CONFIG.md
SIGUSR1 cert rotation · SIGTERM graceful drain ✅ RUNBOOK.md
↳ proactive per-protocol drain signal (H1 Connection: close / H2 GOAWAY / H3 CONNECTION_CLOSE) ⏳ in progress; today = lameduck + bounded drain + force-close — ../known-limitations.md
Binary hot-restart via socket-descriptor handover ⚠️ deferred (SO_REUSEPORT side-by-side only) deployment-patterns.md
Per-IP + in-flight connection caps ✅ CONFIG.md
Topology / HA (stateless; no built-in clustering) ⚠️ deployment-patterns.md
Prometheus /metrics + k8s probes; LB_LOG_FORMAT ✅ METRICS.md

Security posture

The security audit closed at 0 Critical / 0 High / 1 Medium (fixed) / 7 Low / 4 Info. Production wire parsing is delegated to hyper (H1/H2), quiche/BoringSSL (H3/QUIC/TLS), rustls (TLS), and tungstenite (WS); the only hand-rolled production parser is the Mode A QUIC public-header reader, which is panic-free by construction and was fuzzed extensively. Full record: ../../SECURITY.md.