Rails4.2+Nginx生产环境随机出现end of file reached错误求助

Hey there, let's break down this tricky random error you're facing—random issues are always the worst, especially when nothing's been changed recently. Let's start by connecting the dots between the end of file reached error on server A and the CORS errors in the browser.

1. Start with Server A's Logs (The Root of the Backend Error) #

First, let's dig into the logs to get context on that end of file reached error—it's usually a clue that a connection was unexpectedly mid-stream:

• Rails Production Logs: Check production.log for the exact timestamp and request ID when the error hits. Look for the full stack trace—does it point to a socket/network operation, or a failure to read a response from another service? This error often pops up when Rails can't finish reading a request/response because the connection dropped.
• Nginx Logs: Cross-reference the same timestamp in Nginx's access.log and error.log. Look for entries like client_abort (which means the browser closed the connection early) or timeout errors. Even if you didn't change configs, sudden traffic spikes or resource constraints could trigger timeouts.
• Check Nginx Timeout Settings: Verify proxy_read_timeout and proxy_connect_timeout in your Nginx config for server A. If these are set too low, a slow response or network blip could cause the connection to drop before Rails finishes processing.

2. Tie in the CORS Browser Errors #

The CORS exceptions are likely a side effect of the backend connection failure, but we should rule out CORS config issues too:

• Validate CORS Preflight Requests: Browsers send an OPTIONS preflight request before the actual AJAX call. Use curl to simulate this and check if server A responds correctly:

  curl -X OPTIONS -H "Origin: https://www.myserver.com" -H "Access-Control-Request-Method: GET" https://app.myserver.com/header -v
  

  Ensure the response includes Access-Control-Allow-Origin, Access-Control-Allow-Methods, and returns a 200/204 status code. Missing or incomplete headers here could trigger CORS errors, especially if the connection drops mid-response.
• Check Rack-Cors Config: If you're using the rack-cors gem, double-check your initializer to make sure it explicitly allows the OPTIONS method and the origin www.myserver.com. Even if it worked before, a cached middleware state or subtle config drift could cause issues.

3. Rule Out Network & Infrastructure Changes #

Since neither server was modified, the problem might lie in the middle:

• Test Server-to-Server Connectivity: Use mtr or traceroute between server B and A to monitor for packet loss or latency spikes over time:

  mtr --report app.myserver.com
  

  This can uncover intermittent network issues from ISPs, firewalls, or load balancers that you might not control.
• Check Server Resource Limits:
  • File descriptors: Run ulimit -n to see the max allowed, and lsof | wc -l to count current usage. If you're hitting the limit, Rails can't open new connections, leading to drops.
  • CPU/Memory/Disk: Use top, htop, or df -h to ensure server A isn't running out of resources. Long-running production environments can develop memory leaks or disk bloat over time.
• Check for Unplanned System Updates: Even if you didn't push changes, automatic system updates (like Ubuntu's unattended-upgrades) might have updated Nginx, Ruby, or kernel libraries. Check update logs with cat /var/log/apt/history.log (Debian/Ubuntu) or /var/log/yum.log (CentOS).

4. Rails-Specific Troubleshooting #

• Connection Pool Limits: If your endpoint uses a database, Redis, or another service, check if the connection pool is exhausted. A full pool can cause requests to queue and eventually time out.
• Restart Services: Sometimes long-running Rails processes or Nginx workers develop weird state issues. Try restarting both on server A—this is a quick test to rule out transient bugs.
• Reproduce with Load Testing: Use ab (Apache Bench) to simulate concurrent requests and see if you can trigger the error consistently:

  ab -n 1000 -c 10 -H "Origin: https://www.myserver.com" https://app.myserver.com/header
  

  This can help confirm if the issue is tied to high load or concurrency.

Possible Quick Fixes to Try #

• Adjust Nginx Timeouts: Extend proxy_read_timeout to 120s in your Nginx location block for server A to give slow requests more time to complete.
• Increase File Descriptor Limits: Update /etc/security/limits.conf to raise limits for your web user (e.g., www-data):

  www-data soft nofile 65535
  www-data hard nofile 65535
  

• Re-Rack CORS Middleware: Ensure the rack-cors middleware is loaded early in the stack (before other middleware that might intercept OPTIONS requests).

内容的提问来源于stack exchange，提问作者Filip Kis