503 Service unavailable with a AJAX request

[Julien Escario]

Hi everyone,
I'm pretty newbie to varnish and trying to place one instance in front of a 
whole shared hosting webserver to reduce the load.

One of my customer discovered that when trying to access the backoffice of a 
prestashop site (http://www.prestashop.com/en/), the system is sending back an 
error 503.

The URL is a POST like this (as said by varnishncsa) :
POST http://www.eric-collection.com/cpanel/index.php?tab=AdminCatalog HTTP/1.1

This is a clickable image that calls a javascript function :
onclick="getE('submitFilterproduct').value=2"

getE() seems to be an alias for getElementByID.

This why I'm thinking of some kind of AJAX call.

I'm using varnish 2.1.4 SVN

You'll find below the full log of this specific request. I don't know what else 
can be checked.

Any idea on the problem and how to solve it ?

Thanks you,
Julien


    13 SessionOpen  c 92.61.134.71 49973 :80
    13 Debug        c "herding"
    13 ReqStart     c 92.61.134.71 49973 2059649223
    13 RxRequest    c POST
    13 RxURL        c /cpanel/index.php?tab=AdminCatalog
    13 RxProtocol   c HTTP/1.1
    13 RxHeader     c Host: www.eric-collections.com
    13 RxHeader     c User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; fr; 
rv:1.9.2.12) Gecko/20101027 Ubuntu/10.10 (maverick) Firefox/3.6.12
    13 RxHeader     c Accept: 
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
    13 RxHeader     c Accept-Language: fr,fr-fr;q=0.8,en-us;q=0.5,en;q=0.3
    13 RxHeader     c Accept-Encoding: gzip,deflate
    13 RxHeader     c Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
    13 RxHeader     c Keep-Alive: 115
    13 RxHeader     c Connection: keep-alive
    13 RxHeader     c Referer: 
http://www.eric-collections.com/cpanel/index.php?tab=AdminCatalog&token=8bafcd5a500a1187d95c84dfee08500d
    13 RxHeader     c Cookie: 
0a5b149381233bf1a5aa73686b19a724=vy8IX3rzLh0%3Dtx%2F3VNEwdYI%3DKCu0a1iJlWE%3Dc2L2J40kVJE%3DrbrbQ5PPJAM%3DWrAle2ZpCyU%3D%2F1t3yafkMjo%3DOx1P3aPPQkI%3DFlsCzVKOMVE%3DhrfaeVftAsY%3DjjOOPo6co40%3Dw9ft%2BGoWuLU%3D4AF3J5oZxrM%3DAjhM7HUC5TU%3DCJsJh7dlH0c%
    13 RxHeader     c Content-Type: application/x-www-form-urlencoded
    13 RxHeader     c Content-Length: 283
    13 VCL_call     c recv
    13 VCL_return   c pass
    13 VCL_call     c hash
    13 VCL_return   c hash
    13 VCL_call     c pass
    13 VCL_return   c pass
    14 BackendClose - default
    14 BackendOpen  b default 195.200.217.243 51495 195.200.217.2 80
    13 Backend      c 14 default default
    14 TxRequest    b POST
    14 TxURL        b /cpanel/index.php?tab=AdminCatalog
    14 TxProtocol   b HTTP/1.1
    14 TxHeader     b Host: www.eric-collections.com
    14 TxHeader     b User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; fr; 
rv:1.9.2.12) Gecko/20101027 Ubuntu/10.10 (maverick) Firefox/3.6.12
    14 TxHeader     b Accept: 
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
    14 TxHeader     b Accept-Language: fr,fr-fr;q=0.8,en-us;q=0.5,en;q=0.3
    14 TxHeader     b Accept-Encoding: gzip,deflate
    14 TxHeader     b Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
    14 TxHeader     b Referer: 
http://www.eric-collections.com/cpanel/index.php?tab=AdminCatalog&token=8bafcd5a500a1187d95c84dfee08500d
    14 TxHeader     b Cookie: 
0a5b149381233bf1a5aa73686b19a724=vy8IX3rzLh0%3Dtx%2F3VNEwdYI%3DKCu0a1iJlWE%3Dc2L2J40kVJE%3DrbrbQ5PPJAM%3DWrAle2ZpCyU%3D%2F1t3yafkMjo%3DOx1P3aPPQkI%3DFlsCzVKOMVE%3DhrfaeVftAsY%3DjjOOPo6co40%3Dw9ft%2BGoWhLU%3D4AF3J5oZxrM%3DAjhM7HUC5TU%3DCJsJh7dlH0c%
    14 TxHeader     b Content-Type: application/x-www-form-urlencoded
    14 TxHeader     b Content-Length: 283
    14 TxHeader     b X-Forwarded-For: 92.61.134.71
    14 TxHeader     b X-Varnish: 2059649223
    13 FetchError   c http first read error: -2 0 (Success)
    14 BackendClose b default
    13 VCL_call     c error
    13 VCL_return   c deliver
    13 VCL_call     c deliver
    13 VCL_return   c deliver
    13 TxProtocol   c HTTP/1.1
    13 TxStatus     c 503
    13 TxResponse   c Service Unavailable
    13 TxHeader     c Server: Varnish
    13 TxHeader     c Retry-After: 0
    13 TxHeader     c Content-Type: text/html; charset=utf-8
    13 TxHeader     c Content-Length: 419
    13 TxHeader     c Date: Thu, 28 Oct 2010 14:20:53 GMT
    13 TxHeader     c X-Varnish: 2059649223
    13 TxHeader     c Age: 3
    13 TxHeader     c Via: 1.1 varnish
    13 TxHeader     c Connection: close
    13 Length       c 419
    13 ReqEnd       c 2059649223 1288275650.343024969 1288275653.194123983 
0.004972935 2.851063013 0.000036001
    13 SessionClose c error
    13 StatSess     c 92.61.134.71 49973 3 1 1 0 1 0 235 419