Troubleshooting & Debugging

GDN Network Troubleshooting

To troubleshoot GDN network problems effectively, it’s essential to have a clear picture of the traffic routing flow. The most common issues in GDN network setup are due to misconfiguration of DNS, the proxy, or the GDN domain and segment settings. 

A more systematic approach to troubleshooting is to check each ‘hop’ of the route from web browser to origin server in order to locate where the failure is happening. The key actions that take place at each hop and sample problems are shown in the table below. 

 

Action

Potential Problems

Troubleshooting Approach

Receive and process HTTP request

Request not received

Request wrong in some way (e.g., wrong Host header or URI path)

Check server access logs to confirm.
Likely cause: misconfiguration in downstream proxy.

DNS lookup for IP address of next server in route

DNS lookup failure

Check server access logs to confirm.

Manually run DNS lookup on the server using host
command.
Likely causes: DNS lookup misconfigured on server (e.g., resolver entry in Nginx); DNS entries wrong.

Establish TCP connection to next server

Fail to open connection

Check server access logs to confirm.

Manually attempt connection from server using curl command.
Likely causes: firewall blocking--may require whitelisting; upstream server down; upstream server listening on a different port.

Establish TLS/SSL session (if HTTPS)

Fail to establish TLS session

Check server access logs to confirm.

Manually check certificate presented by upstream server using openssl command.

Likely causes: certificate doesn’t match hostname; certificate not trusted; SNI enabled/disabled.

Send HTTP request; receive HTTP response

Timeout awaiting response.

5xx gateway error.

403 forbidden.

Looping request.

Other error response.

Check server access logs to confirm.

Manually send request  through server using curl command and examine response. If 5xx, run curl from server. Use __smartling/api/headers.htm to see headers sent upstream from GDN.
Likely causes: request incorrect in some way for upstream processing; whitelisting.



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