503 error from varnish

[Geoff Simmons]

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On 7/5/15 2:54 AM, Tim Dunphy wrote:
> 
> But my current problem is that I've been able to get the main page
> to the site cached, and a few others. But when I click to like the
> 4th or 5th page on the wiki that I want to cache through varnish,
> everything comes to a halt. I get a 503 - service unavailable
> error, instead of varnish going to the web server to retrieve the
> page I had clicked on.

503 errors are in most cases an indication that there's a problem with
your backends, and Varnish cannot retrieve responses. When that
happens, you'll often get some info from the log in the FetchError
line, as you did here:

> 10 FetchError   c no backend connection

No backend connection usually means that health checks are failing --
in your case, they're failing for both backends that are assigned to
your director. When health checks fail, Varnish doesn't attempt a
fetch at all and sends a 503 response immediately.

When you see that, check the Backend_health entries in the log. They
describe the current health state (you'll probably see "Still sick"),
and at the end of the log entry they either show the response status
that the checks are getting; or if they show no response status, then
the checks aren't getting any response. That should help you diagnose
the problem.


HTH,
Geoff
- -- 
UPLEX Systemoptimierung
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http://uplex.de/
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