Implement Graceful Shutdown with In-Flight Drain - The Networker

                      TASK
                    

Implementation

Implement graceful shutdown: when the server receives a shutdown signal, it should drain all in-flight requests before closing sockets. New connections are rejected during draining.

Implement handlers:

Request:  {"type": "tcp_request", "msg_id": 1, "data": "process_this", "latency_ms": 500}
Response: {"type": "tcp_request_ok", "in_reply_to": 1, "result": "processed", "duration_ms": 500}

Request:  {"type": "tcp_shutdown", "msg_id": 2, "drain_timeout_ms": 5000}
Response: {"type": "tcp_shutdown_ok", "in_reply_to": 2, "status": "draining", "in_flight": 2}

Request:  {"type": "tcp_request", "msg_id": 3, "data": "new_request", "latency_ms": 100}
Response: {"type": "tcp_request_error", "in_reply_to": 3, "error": "server_shutting_down"}

Request:  {"type": "tcp_drain_status", "msg_id": 4}
Response: {"type": "tcp_drain_status_ok", "in_reply_to": 4, "status": "drained", "remaining": 0, "took_ms": 500}

Sample Test Cases

Normal request processingTimeout: 5000ms

Input

{"src":"c0","dest":"n1","body":{"type":"init","msg_id":1,"node_id":"n1","node_ids":["n1"]}}
{"src":"c1","dest":"n1","body":{"type":"tcp_request","msg_id":2,"data":"hello","latency_ms":0}}

Expected Output

{"src": "n1", "dest": "c0", "body": {"type": "init_ok", "in_reply_to": 1, "msg_id": 0}}
{"src": "n1", "dest": "c1", "body": {"type": "tcp_request_ok", "in_reply_to": 2, "result": "processed", "duration_ms": 0, "msg_id": 1}}

Shutdown starts drainTimeout: 5000ms

Input

{"src":"c0","dest":"n1","body":{"type":"init","msg_id":1,"node_id":"n1","node_ids":["n1"]}}
{"src":"c1","dest":"n1","body":{"type":"tcp_shutdown","msg_id":2,"drain_timeout_ms":5000}}

Expected Output

{"src": "n1", "dest": "c0", "body": {"type": "init_ok", "in_reply_to": 1, "msg_id": 0}}
{"src": "n1", "dest": "c1", "body": {"type": "tcp_shutdown_ok", "in_reply_to": 2, "status": "draining", "in_flight": 0, "msg_id": 1}}

Hints

Hint 1▾

On shutdown signal, stop accepting new connections immediately

Hint 2▾

Wait for all in-flight requests to complete before closing sockets

Hint 3▾

Track the number of in-flight requests with a counter

Hint 4▾

Set a maximum drain timeout: force-close after N seconds

Hint 5▾

Test by sending requests and initiating shutdown mid-flight

Resources

Graceful Shutdown in Go

How Go standard library implements graceful HTTP server shutdown

                      OVERVIEW
                    

Theoretical Hub

Concept overview coming soon

Key Concepts

graceful shutdowndrainin-flight requestsconnection lifecycle

main.py

python