Implement Path-Based Routing - Load Balancers

Implementation

Path-based routing directs requests to different backend pools based on the URL path. This enables microservices architecture where /api/* routes to API servers and /static/* routes to CDN/static servers.

Routing rules:

/api/*              → api-backend-pool
/api/users/*       → users-service-pool (more specific)
/static/*          → static-backend-pool
/images/*          → image-backend-pool
/admin/*           → admin-backend-pool

Longest-prefix matching:

Request: /api/users/123
  - Matches /api/*           (priority: 1)
  - Matches /api/users/*     (priority: 2) ✓ MORE SPECIFIC
  → Route to users-service-pool

URL rewriting:

Client request: GET /api/v1/users
  ↓ (proxy rewrites)
Backend request: GET /v1/users
  ↓ (backend responds)
Proxy response: HTTP/1.1 200 OK

Example routing:

Request:  {"type": "http_request", "msg_id": 1, "method": "GET", "path": "/api/users/123", "headers": {"Host": "example.com"}}
Response: {"type": "http_response", "in_reply_to": 1, "status": 200, "backend": "users-1", "rewritten_path": "/users/123"}

Routing table configuration:

{
  "routes": [
    {"path_pattern": "/api/users/*", "backend_pool": "users", "rewrite": { "strip_prefix": "/api" }},
    {"path_pattern": "/api/*", "backend_pool": "api", "rewrite": { "strip_prefix": "/api" }},
    {"path_pattern": "/static/*", "backend_pool": "static", "rewrite": {}},
    {"path_pattern": "/images/*", "backend_pool": "images", "rewrite": {}}
  ]
}

Sample Test Cases

Route /api/users to users poolTimeout: 5000ms

Input

{
  "src": "client",
  "dest": "l7_proxy",
  "body": {
    "type": "http_request",
    "msg_id": 1,
    "method": "GET",
    "path": "/api/users/123",
    "headers": {
      "Host": "example.com"
    }
  }
}

Expected Output

{"src": "l7_proxy", "dest": "client", "body": {"type": "http_response", "in_reply_to": 1, "status": 200, "backend": "users-1", "rewritten_path": "/users/123"}}

Route /api/posts to api poolTimeout: 5000ms

Input

{
  "src": "client",
  "dest": "l7_proxy",
  "body": {
    "type": "http_request",
    "msg_id": 1,
    "method": "GET",
    "path": "/api/posts/456",
    "headers": {
      "Host": "example.com"
    }
  }
}

Expected Output

{"src": "l7_proxy", "dest": "client", "body": {"type": "http_response", "in_reply_to": 1, "status": 200, "backend": "api-1", "rewritten_path": "/posts/456"}}

Hints

Hint 1▾

Match URL paths against routing rules: /api/* → api pool, /static/* → static pool

Hint 2▾

Use longest-prefix matching: /api/users/auth matches /api/users/* not just /api/*

Hint 3▾

Implement URL rewriting: strip /api prefix before forwarding to backend

Hint 4▾

Support wildcards: /api/v* matches /api/v1, /api/v2

Hint 5▾

Return 404 if no route matches

Implementation

Sample Test Cases

Hints

Resources

Theoretical Hub

Key Concepts