![]() ![]() Now we can read all the failed requests from the binary log that is being recorded by the varnishlog daemon. You can then enable the logging with: sudo systemctl enable -now varnishlog This overrides the default startup command of the service, to log only failed requests. Run: sudo systemctl edit varnishlogĮxecStart=/usr/bin/varnishlog -a -w /var/log/varnish/varnish.log -D -P /run/varnishlog/varnishlog.pid -q "(RespStatus >= 500 and RespStatus = 500 and BerespStatus <= 599)" Let’s enable varnishlog service which logs only failed requests. Varnish memory log obviously can’t hold for a long period of logged data. One issue with the above approaches is that they allow us to lookup only recent requests. Enable varnishlog service for collecting longer history of failed requests Now we can investigate the file and find out details about why we have failed requests. varnishlog -A -d -w /var/log/varnish/varnish50x.log -q "RespStatus >= 500 or BerespStatus >= 500" A better approach is to save in-memory Varnish log entries into a file. It may produce too many entries and quickly fill your screen. Will show the latest in-memory Varnish log entries for “Backend fetch failed”. Use varnishlog to see all failed requests varnishlog -d -q "BerespStatus = 503" In the former case, run: varnishlog -d -q 'BereqHeader:X-Varnish = 12345' If the previous commands do not return any request, it means that the 12345 represents the ID of backend request, or the memory log was already overwritten by new requests. Review request details of Varnish connection to the backend: varnishlog -d -q 'BereqHeader:X-Varnish = 12346' Find a line that looks like this: - Link bereq 12346 pass Investigate it for the ID of the backend request. This will display the client-side request to Varnish. The “Backend fetch failed” may be triggered before communicating the backend, or after.įirst, you will get client side request using the following command: varnishlog -d -q 'RespHeader:X-Varnish = 12345' In versions prior to 5.1 you can use the X-Varnish header: Use that number to get relevant requests quickly. When you get “Backend fetch failed” in the browser, take note of “XID: 12345” at the bottom of the page. It much better to hunt down the specific request that generated the error. Use varnishlog to see why backend fetch failed for particular request The solution is often to return (pipe) for large files Varnish cannot find an object to evict from the cache while serving large files ( ExpKill LRU_Exhausted and FetchError Could not get storage in varnishlog), similar to this issue.Varnish can’t communicate to the backend.Your PHP has generated a fatal error (HTTP code > 500).A backend health probe failed – your backend is marked as sick. ![]() Why backend fetch failsĬommon reasons for getting “Backend fetch failed” error: Here are some generic tips on finding the actual cause of the “Backend Fetch Failed” error shown by Varnish Cache. If you want to install NGINX, Varnish, and lots of useful performance/security software with smooth yum upgrades for production use, this is the repository for you. We have by far the largest RPM repository with NGINX module packages and VMODs for Varnish. ![]()
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