Varnish 503 responses

[Erick Faustino]

Hi, everybody!

We are using varnish, to cache our website. We are using varnish inside
AWS, so we have an ELB with 2 instances (autoscaling) with varnish + nginx.
Everything is fine, until the backend application has some fails (5xx
responses) or timeouts then varnish has much more 5xx responses than the
backend.

 For example: If backend respond 300 reqs with 5xx http status, varnish
delivers some stale content (thats ok and expected due our vcl config), but
the 5xx responses is ten times or more than backend, like 5000.
I think that the responses from varnish, should be very similar with the
backend, right? Why this happens? Where can I look to clarify this?
(varnishstat, varnishlog, varnishncsa log and etc). I would appreciate any
help. If you need more information about my config, feel free to ask.

Best regards,

Erick Faustino
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