I was observing a behavior of a PHP script on one backend server that got 
executed/requested 
twice (but not by the client/browser).

The plain script just processes data and only outputs a response until its 
done. The observed 
behavior is; when first_byte_timeout passes but the script is still processing 
data, the varnish 
node answers with an 503 and the script gets listed twice in the webserver 
process list. So, either 
it gets requested on this event again or the TCP connection close triggers an 
new execution. In any
case its a bug and because of missing resources to dive into a more deeper 
analyses, I just disabled 
the enabled keep-alive option of the backend webserver (apache/httpd). The 
results: it helped to avoid 
a further execution of the script. 

The question is: What is the best practice to configure the backend webservers? 
Do you keep the 
keep-alive option enabled or not? 

I'd appreciate hearing your suggestions.

Leon







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