Too many 503 backend errors

[Anand Shah]

I immediately fired a test call using CURL which indicated me a
tcp_miss and i also got the response from origin.

So backend was working and in healthy state.



 [root at mymachine ~]# curl --head --header host:imads.mydomain.com
"http://localhost//0/OasDefault/IIPM_CPL_Nov10_B3_MW/iipm_winter02_300x600_10dec_03.gif"
  HTTP/1.1 200 OK
  Last-Modified: Thu, 02 Dec 2010 12:19:14 GMT
  P3P: CP="NON NID PSAa PSDa OUR IND UNI COM NAV STA",policyref="/w3c/p3p.xml"
  Content-Type: image/gif
  cache-control: max-age=604800
  Content-Length: 4150
  Date: Wed, 22 Dec 2010 06:39:26 GMT
  Connection: keep-alive
  H-Served-By: mymachine
  Server: mydomain/2.0.6
  X-Cache: TCP_MISS

  [root at mymachine ~]# curl --head --header host:imads.mydomain.com
"http://localhost//0/OasDefault/IIPM_CPL_Nov10_B3_MW/iipm_winter02_300x600_10dec_03.gif"
  HTTP/1.1 200 OK
  Last-Modified: Thu, 02 Dec 2010 12:19:14 GMT
  P3P: CP="NON NID PSAa PSDa OUR IND UNI COM NAV STA",policyref="/w3c/p3p.xml"
  Content-Type: image/gif
  cache-control: max-age=604800
  Content-Length: 4150
  Date: Wed, 22 Dec 2010 06:39:33 GMT
  Connection: keep-alive
  H-Served-By: mymachine
  Server: mydomain/2.0.6
  X-Cache: TCP_HIT




Regards,
   Anand

On Wed, Dec 22, 2010 at 12:42:24PM +0530, Anand Shah wrote:
> I am running varnish on 64 bit Centos. Getting too many 503 errors
> recently and i tried debugging it with some help from Forums on
> mailinglist.

> VARNISHLOGS:
>
>   180 VCL_call     c miss fetch
>   180 FetchError   c no backend connection
>   180 VCL_call     c error deliver

In my experience, "no backend connection" indicates that whatever
backend was selected to handle this request was unavailable due to the
health check/probe returning an error.

What was the backend health at the time? You can use the 'debug.health'
command in the CLI to view health information, or

  varnishlog -i Backend_health

to see the results of the health checks as they occur. If a backend is
marked as 'sick' then Varnish won't send any requests to it, since
it's unlikely to help the situation.

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