title: varnish 503 service unavailable
body: <p>My varnish version is <code>3.0</code>.</p>
  
  <p>My server works well while I curl the URLs, but when use varnish cache it return <code>503 service unavailable</code> occasionally.</p>
  
  <p>The log info likes is:</p>
  
  <pre><code>0 Debug        - "VCL_error(200, OK)"
  24 VCL_call     c recv error
  24 VCL_call     c error deliver
  24 SessionClose c error
  0 Debug        - "VCL_error(200, OK)"
  27 VCL_call     c recv error
  27 VCL_call     c error deliver
  27 SessionClose c error
  0 Debug        - "VCL_error(200, OK)"
  16 VCL_call     c recv error
  16 VCL_call     c error deliver
  16 SessionClose c error
  14 Debug        - "Write error, retval = 2998272, len = 8465870, errno = Success"
  0 Debug        - "VCL_error(200, OK)"
  14 VCL_call     c recv error
  14 VCL_call     c error deliver
  14 SessionClose c error
  0 Debug        - "VCL_error(200, OK)"
  21 VCL_call     c recv error
  21 VCL_call     c error deliver
  21 SessionClose c error
  </code></pre>
  
  <p>PS:The server response 200 when I curl or type the urls on browsers.</p>