# rws as a Proxy Server — Config-Driven Design
This document specifies the configuration schema for evolving `rws` from a static file server into a config-driven proxy and web server platform comparable to nginx, Caddy, Traefik, and HAProxy. No Rust code should be required to configure routing, proxying, TLS, or middleware.
---
## Design principles
1. **Config-driven** — every capability expressible in `rws.config.toml` (or env vars). The binary reads config at startup and wires the middleware stack automatically.
2. **Backward compatible** — existing `rws.config.toml` fields keep working unchanged.
3. **TOML-native** — use `[[route]]` array-of-tables for location blocks, `[[upstream]]` for backend pools. No custom DSL.
4. **Layered middleware per route** — each route can declare its own middleware stack (auth, rate limit, rewrite, cache) without affecting others.
5. **Hot reload** — SIGHUP or `POST /admin/config/reload` re-applies the full config without restart, including route table changes.
---
## Full annotated `rws.config.toml`
```toml
# ── Server ────────────────────────────────────────────────────────────────────
ip = "0.0.0.0"
port = 443
thread_count = 512
request-allocation-size-in-bytes = 65536
# Optional: redirect plain HTTP on this port to HTTPS.
http_redirect_port = 80
# ── TLS ───────────────────────────────────────────────────────────────────────
tls_cert_file = "/etc/rws/certs/default.crt"
tls_key_file = "/etc/rws/certs/default.key"
# mTLS: require clients to present a certificate signed by this CA.
# tls_client_ca_file = "/etc/rws/certs/ca.pem"
# ── Virtual hosts (SNI-based cert selection) ──────────────────────────────────
[[virtual_host]]
domain = "api.example.com"
cert_file = "/etc/rws/certs/api.crt"
key_file = "/etc/rws/certs/api.key"
[[virtual_host]]
domain = "www.example.com"
cert_file = "/etc/rws/certs/www.crt"
key_file = "/etc/rws/certs/www.key"
# ── Automatic TLS via ACME (Let's Encrypt) ────────────────────────────────────
# Requires `--features acme`. Provisions and renews certs automatically.
# [acme]
# domains = ["api.example.com", "www.example.com"]
# email = "ops@example.com"
# ── Upstream pools ────────────────────────────────────────────────────────────
# Named groups of backends used by proxy routes.
# strategy: "round_robin" (default) | "least_conn" | "ip_hash" | "random"
[[upstream]]
name = "api-backends"
strategy = "round_robin"
backends = ["10.0.0.10:8080", "10.0.0.11:8080", "10.0.0.12:8080"]
[upstream.health_check]
path = "/healthz" # HTTP GET path to probe
interval_secs = 10
timeout_ms = 2000
healthy_threshold = 2 # consecutive successes to mark up
unhealthy_threshold = 3 # consecutive failures to mark down
[[upstream]]
name = "grpc-service"
strategy = "round_robin"
backends = ["h2://grpc1:50051", "h2://grpc2:50051"]
[[upstream]]
name = "static-origin"
strategy = "round_robin"
backends = ["https://storage.example.com"]
# ── Routes ────────────────────────────────────────────────────────────────────
# Evaluated top-to-bottom; first match wins.
# Each route has a [match] block and an [action] block.
# Optional [middleware] block declares per-route middleware layers.
# ── Route 1: API reverse proxy ────────────────────────────────────────────────
[[route]]
name = "api-proxy"
[route.match]
host = "api.example.com" # SNI / Host header; omit to match any host
path = "/v1/*" # prefix match; use exact = "/v1/ping" for exact
[route.action]
type = "proxy"
upstream = "api-backends" # references [[upstream]] name above
[route.action.proxy]
connect_timeout_ms = 1000
read_timeout_ms = 10000
strip_path_prefix = "/v1" # strip before forwarding
add_path_prefix = "/api/v1" # prepend after strip
upstream_scheme = "http" # "http" | "https" | "h2"
[route.middleware]
rate_limit = { max_requests = 500, window_secs = 60 }
auth = { type = "jwt", secret_env = "JWT_SECRET" }
[[route.middleware.rewrite.request]]
type = "header_set"
name = "X-Forwarded-Host"
value = "api.example.com"
[[route.middleware.rewrite.response]]
type = "header_set"
name = "Cache-Control"
value = "no-store"
# ── Route 2: gRPC proxy ───────────────────────────────────────────────────────
[[route]]
name = "grpc-proxy"
[route.match]
host = "api.example.com"
content_type = "application/grpc*" # match on Content-Type prefix
[route.action]
type = "grpc"
upstream = "grpc-service"
[route.action.proxy]
connect_timeout_ms = 1000
read_timeout_ms = 30000
# ── Route 3: static files ─────────────────────────────────────────────────────
[[route]]
name = "static-site"
[route.match]
host = "www.example.com"
path = "/*"
[route.action]
type = "static"
root = "/var/www/html" # serve files from this directory
index = ["index.html", "index.htm"]
directory_listing = false
[route.middleware]
cache = { ttl_secs = 3600, vary_by = ["Accept-Encoding"] }
[[route.middleware.rewrite.response]]
type = "header_set"
name = "Cache-Control"
value = "public, max-age=3600"
# ── Route 4: redirect ─────────────────────────────────────────────────────────
[[route]]
name = "www-redirect"
[route.match]
host = "example.com"
path = "/*"
[route.action]
type = "redirect"
location = "https://www.example.com$path"
status = 301
# ── Route 5: basic auth protected area ───────────────────────────────────────
[[route]]
name = "admin-area"
[route.match]
host = "www.example.com"
path = "/admin/*"
[route.action]
type = "static"
root = "/var/www/admin"
[route.middleware]
auth = { type = "basic", users_file = "/etc/rws/htpasswd" }
# ── Route 6: MCP endpoint ─────────────────────────────────────────────────────
[[route]]
name = "mcp"
[route.match]
path = "/mcp"
method = "POST"
[route.action]
type = "mcp" # built-in MCP server
[route.middleware]
auth = { type = "bearer", token_env = "MCP_TOKEN" }
# ── Route 7: catch-all 404 ────────────────────────────────────────────────────
[[route]]
name = "not-found"
[route.match]
path = "/*"
[route.action]
type = "respond"
status = 404
body = "Not Found"
# ── TCP proxy (L4, runs a separate listener) ──────────────────────────────────
[[tcp_proxy]]
name = "postgres"
listen = "0.0.0.0:5432"
backends = ["db1:5432", "db2:5432"]
strategy = "round_robin"
connect_timeout_ms = 500
[[tcp_proxy]]
name = "redis"
listen = "0.0.0.0:6379"
backends = ["cache1:6379"]
# ── UDP proxy ─────────────────────────────────────────────────────────────────
[[udp_proxy]]
name = "dns"
listen = "0.0.0.0:53"
backends = ["8.8.8.8:53", "1.1.1.1:53"]
strategy = "round_robin"
reply_timeout_ms = 2000
buffer_size = 8192
# ── WebSocket proxy ───────────────────────────────────────────────────────────
# WsProxy runs a separate listener (raw upgrade + byte relay).
[[ws_proxy]]
name = "chat"
listen = "0.0.0.0:9000"
backends = ["ws-backend1:8080", "ws-backend2:8080"]
connect_timeout_ms = 500
read_timeout_ms = 30000
# ── Global middleware defaults ────────────────────────────────────────────────
# Applied to all [[route]] blocks unless the route overrides them.
[middleware]
rate_limit = { max_requests = 1000, window_secs = 60 }
log_format = "json" # "combined" | "json"
[[middleware.rewrite.response]]
type = "header_remove"
name = "X-Powered-By"
[[middleware.rewrite.response]]
type = "header_set"
name = "X-Content-Type-Options"
value = "nosniff"
# ── CORS ──────────────────────────────────────────────────────────────────────
[cors]
allow_all = false
allow_origins = ["https://www.example.com"]
allow_methods = ["GET", "POST", "PUT", "PATCH", "DELETE"]
allow_headers = ["content-type", "authorization"]
allow_credentials = true
expose_headers = ["content-type"]
max_age = "86400"
```
---
## Route matching rules
Matches are evaluated in the order listed in the config file. First match wins. All match fields within a single `[route.match]` block are ANDed together.
| `host` | string | Exact SNI / `Host` header match. Omit to match any host. |
| `path` | string | Prefix match when ending with `/*`; exact match otherwise. |
| `method` | string | HTTP method (`GET`, `POST`, …). Omit to match any method. |
| `content_type` | string | `Content-Type` prefix match (e.g. `application/grpc*`). |
---
## Action types
| `proxy` | Forward to an `[[upstream]]` pool over HTTP/1.1 |
| `grpc` | Forward to an `[[upstream]]` pool over HTTP/2 (`Content-Type: application/grpc*` enforced) |
| `static` | Serve files from a local directory |
| `redirect` | Return a 301/302 with a `Location` header; `$path` is substituted |
| `respond` | Return a fixed status + body (useful for maintenance, 404 catch-all) |
| `mcp` | Activate the built-in MCP Streamable HTTP server |
---
## Per-route middleware
All middleware keys under `[route.middleware]` are optional. Absent keys inherit global defaults.
| `rate_limit` | `{ max_requests, window_secs }` | Per-client-IP sliding-window; returns 429 |
| `cache` | `{ ttl_secs, vary_by }` | In-memory GET cache |
| `auth.type = "basic"` | `{ users_file }` | HTTP Basic auth against an htpasswd file |
| `auth.type = "jwt"` | `{ secret_env }` | HS256 JWT via `Authorization: Bearer` |
| `auth.type = "bearer"` | `{ token_env }` | Static bearer token comparison |
| `rewrite.request[]` | array of rules | Transform the request before forwarding |
| `rewrite.response[]` | array of rules | Transform the response before returning |
| `ip_filter.allow` | array of CIDR strings | Allowlist; 403 for non-matching IPs |
| `ip_filter.deny` | array of CIDR strings | Denylist; 403 for matching IPs |
---
## Rewrite rule types
Rules in `rewrite.request[]` and `rewrite.response[]` arrays:
| `header_set` | `name`, `value` | Add or replace a header |
| `header_remove` | `name` | Remove a header |
| `uri_set` | `value` | Replace the entire request URI |
| `uri_strip_prefix` | `prefix` | Remove a path prefix |
| `uri_add_prefix` | `prefix` | Prepend to the URI |
| `status_set` | `code`, `reason` | Override response status (response only) |
| `body_replace` | `from`, `to` | Byte-level find-and-replace in response body |
---
## Upstream health checks
When `[upstream.health_check]` is present, a background task probes each backend at `interval_secs`. Backends that fail `unhealthy_threshold` consecutive probes are removed from the rotation. They are re-added after `healthy_threshold` consecutive successes. The proxy always returns `502` if no healthy backend is available.
Health check state is visible via `GET /metrics` (Prometheus) and the `server_metrics` MCP tool.
---
## Load balancing strategies
| `round_robin` | Distribute requests in order (default) |
| `least_conn` | Send to the backend with the fewest active connections |
| `ip_hash` | Hash client IP to a backend for session affinity |
| `random` | Pick a backend at random |
---
## Implementation plan
The following pieces need to be built or extended for full config-driven operation:
### Phase 1 — Config schema + route table (highest value)
1. Extend `src/entry_point/mod.rs` to parse `[[upstream]]`, `[[route]]`, `[[tcp_proxy]]`, `[[udp_proxy]]`, `[[ws_proxy]]` from `rws.config.toml`.
2. Add `RouteConfig`, `UpstreamConfig`, `ActionConfig`, `MiddlewareConfig` structs in a new `src/config/mod.rs`.
3. Build a `src/config/builder.rs` that turns parsed config into a `WithMiddleware<App>` stack at startup — this is the core of the shift.
4. `main.rs` calls `config::build_app_from_config()` instead of the hardcoded `build_app()`.
### Phase 2 — Backend health checks
5. Add `src/health_check/mod.rs` — background thread per upstream pool that probes backends and maintains an `Arc<RwLock<Vec<String>>>` of live backends.
6. `ReverseProxy` reads live backends from the health checker instead of a static list.
### Phase 3 — Load balancing strategies
7. Extend `src/proxy/mod.rs` with `LeastConn` (atomic active-connection counter per backend) and `IpHash` (FNV hash of client IP mod backends) strategies.
### Phase 4 — Upstream TLS
8. Add `https://` backend support to `ReverseProxy` via `rustls` client config.
9. Reuse `load_certs()` from `src/tls/mod.rs`; add `RWS_CONFIG_UPSTREAM_CA_FILE` for custom CA trust.
### Phase 5 — Config-driven TCP/UDP/WS proxies
10. On startup, spawn one thread per `[[tcp_proxy]]`, `[[udp_proxy]]`, `[[ws_proxy]]` block calling `TcpProxy::bind()`, `UdpProxy::bind()`, `WsProxy::bind()` respectively.
11. SIGHUP restarts proxy threads whose config changed.
### Phase 6 — Per-route auth from config
12. Extend `BasicAuthLayer` to load users from an htpasswd file path (not just a closure).
13. `config::builder` wraps matching routes with the appropriate auth layer based on `[route.middleware.auth]`.
### Phase 7 — Static site action
14. The `static` action type is already handled by `StaticResourceController`; expose `root` and `directory_listing` as config fields so the route can override the working directory.
---
## What stays code-driven (library API)
Users who import `rust-web-server` as a library crate keep the existing API — `ReverseProxy::new(...)`, `.wrap(RewriteLayer::new()...)`, etc. The config-driven path is an additional layer on top, not a replacement. The library remains useful for embedding rws in custom Rust applications.