Describe How to Deal with HTTP Error Codes F5N4 Practice Questions (Page 1)

Questions 1–5

1. 1expert · medium

   An NGINX reverse proxy is returning 502 Bad Gateway for requests to an upstream service. The error log shows: 'connect() failed (111: Connection refused) while connecting to upstream'. The upstream service is running and listening on 127.0.0.1:8080. The proxy_pass directive is set to 'http://localhost:8080'. What is the most likely cause?

   • AThe upstream service is not running. Start the upstream service.
   • BThe proxy_read_timeout is set too low, causing NGINX to close the connection. Increase the proxy_read_timeout value.
   • CThe client's request is malformed, causing the upstream to refuse the connection. Fix the client application's request format.
   • DNGINX resolves 'localhost' to an IPv6 address (::1), but the upstream is only listening on IPv4 (127.0.0.1). Change proxy_pass to use 'http://127.0.0.1:8080'.
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2. 2application · medium

   A web application behind NGINX suddenly starts returning 401 responses for a subset of users. The NGINX error log shows no relevant entries, but the access log shows the requests reaching NGINX with a 401 status. The upstream application is healthy and the users' credentials are valid. What is the most likely cause and fix?

   • AThe upstream server is returning 401 due to an expired session token. Restart the upstream application to clear session state.
   • BThe proxy_pass directive is misconfigured, causing NGINX to forward requests to the wrong port. Correct the proxy_pass URL.
   • CThe client's IP address is blocked by the deny directive, returning 401. Remove the deny rule from the server block.
   • DThe auth_basic directive is enabled on the location block, rejecting requests that lack a valid Basic Auth header. Remove or adjust the auth_basic directive.
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4. 3application · medium

   Users report that some images on a website are not loading, and the browser shows 404 Not Found errors. The NGINX access log shows the requests for the images returning 404. The files exist in the web root directory. What is the most likely cause?

   • AThe location block for images is misconfigured, using an alias that points to the wrong directory. Correct the alias directive to point to the actual image directory.
   • BThe upstream server is down, causing NGINX to return 404. Restart the upstream service.
   • CThe images are being blocked by a deny directive, returning 404 instead of 403. Remove the deny rule from the location block.
   • DThe client's browser is caching an old 404 response. Instruct users to clear their browser cache.
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5. 4application · medium

   A user reports receiving a 400 Bad Request error when accessing a website through NGINX. The NGINX error log shows: 'client sent invalid request line'. The user's browser is up to date. What is the most likely cause?

   • AThe upstream server is returning 400 due to a misconfiguration. Fix the upstream server's configuration.
   • BThe server's client_max_body_size is set too low, rejecting the request. Increase the client_max_body_size directive.
   • CThe server's SSL certificate is expired, causing the client to send a malformed request. Renew the SSL certificate.
   • DThe client is sending a malformed HTTP request, possibly due to a proxy or browser extension. Ask the user to disable extensions or try a different browser.
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6. 5application · medium

   An NGINX server is returning 503 Service Unavailable for all requests. The error log shows: 'no live upstreams while connecting to upstream'. The upstream servers are defined in an upstream block and are healthy. What is the most likely cause?

   • AThe server is overloaded, returning 503 to all requests. Increase server resources.
   • BThe client's request is malformed, causing NGINX to return 503. Fix the client application's request format.
   • CAll upstream servers are marked as down due to health check failures or the down parameter. Remove the down parameter or fix the health check configuration.
   • DThe proxy_pass directive is pointing to an incorrect upstream name. Correct the proxy_pass URL.
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