Varnish 503 Error/No backend connection

Question

I'm currently using varnish for my website, previously it was working fine with no problems but today all I am getting is a 503 Error when trying to access any part of my website and this is what I am getting back from varnishlog.

3 VCL_return   c pass                                                                                            
3 FetchError   c no backend connection                                                                           
3 VCL_call     c error                                                                                           
3 VCL_return   c deliver                                                                                         
3 VCL_call     c deliver                                                                                         
3 VCL_return   c deliver                                                                                         
3 TxProtocol   c HTTP/1.1                                                                                        
3 TxStatus     c 503                                                                                             
3 TxResponse   c Service Unavailable                                                                             
3 TxHeader     c Server: Varnish                                                                                 
3 TxHeader     c Retry-After: 0                                                                                  
3 TxHeader     c Content-Type: text/html; charset=utf-8                                                          
3 TxHeader     c Content-Length: 418                                                                             
3 TxHeader     c Date: Sat, 05 Mar 2016 15:25:44 GMT                                                             
3 TxHeader     c X-Varnish: 765008569                                                                            
3 TxHeader     c Age: 0                                                                                          
3 TxHeader     c Via: 1.1 varnish                                                                                
3 TxHeader     c Connection: close                                                                               
3 Length       c 418                                                                                             
3 ReqEnd       c 765008569 1457191544.916952610 1457191544.917085171 0.000094652 0.000080585 0.000051975         
3 SessionClose c error                                                                                           
3 StatSess     c 185.106.92.245 33848 0 1 1 0 1 0 234 418  

Here is my configuration for the vcl

backend default {
.host = "127.0.0.1";
.port = "8080";
.connect_timeout = 1.5s;
.first_byte_timeout = 45s;
.between_bytes_timeout = 30s;
.probe = {
    .url ="/";
    .timeout = 34ms;
    .interval = 1s;
    .window = 10;
    .threshold = 8;
    }
}

sub vcl_recv
{
    # Set Grace Time to one hour
    set req.grace = 1h;
}

sub vcl_fetch
{
    # Set the TTL for cache object to five minutes
    set beresp.ttl = 5m;

    # Set Grace Time to one hour
    set beresp.grace = 1h;
}

I have tried any solutions I can find none of which have improved the situation and my knowledge of this only goes so far. Any help would be appreciated.

Answer 1

In your probe settings you have a very short timeout 34ms

.probe = {
    .url ="/";
    .timeout = 34ms;
    .interval = 1s;
    .window = 10;
    .threshold = 8;
    }

Are you certain your site loads that quickly? If it doesn't then Varnish will mark that backend host as down and will therefore also return the error no backend connection