Retry Mechanism for Failed Proxy Requests

We need a retry mechanism to handle temporary service unavailability and connection failures during proxy requests, something like 'ECONNREFUSED'

Current Behavior

• Single attempt to connect to microservices
• Returns 503 on ECONNREFUSED
• No retry logic for failed requests

Proposed Changes

1. Add retry configuration:

   • Maximum 1-3 retry attempts (configurable)
   • manual delay b/w each failed retry (1s, 2s, 4s) (configurable)
   • 10s timeout per request (configurable)
   • A handler to decide on what basis the retry mechanism will work.

2. Handle specific error cases:

   • ECONNREFUSED
   • ECONNRESET
   • ETIMEDOUT

3. Add response statuses:

   • 503 Service Unavailable (temporary)
   • 504 Gateway Timeout
   • 500 Internal Server Error (other cases)

Code Example

const service_proxy_middleware = (target_url) => { const proxy = createProxyMiddleware({ target: "http://localhost:3002/api/v0/endpoint", changeOrigin: true, logger: console, selfHandleResponse: true, retry: { attempts: 3, delay: 1000, factor: 2, retryCondition: (err) => { return ( err.code === "ECONNREFUSED" || err.code === "ECONNRESET" || err.code === "ETIMEDOUT" ); }, }, on: { proxyReq: fixRequestBody, proxyRes: responseInterceptor(save_to_cache), error: (err, req, res) => { if (err.code === "ECONNREFUSED") { res.status(503).json({ status: "error", message: "Service temporarily unavailable / is restarting, please try again", code: "SERVICE_UNAVAILABLE", }); } else { res.status(500).json({ status: "error", message: "Internal server error", code: "PROXY_ERROR", }); } }, }, }); return proxy; };

Related issue: #176

Additional context (optional)

"http-proxy-middleware": "^3.0.3",
"node": ">=22.0.0",
"express": "^4.21.2"