On Mon, Dec 20, 2010 at 08:04:33AM +0100, Frank Helmschrott wrote: > i wonder how the thing is with keep alive sessions from apache when > using it behind a varnish cache server. Doesn't keep alive make sense > here as all the connection come from the varnish cache (one source) > instead of the users (many sources). I don't know how these sessions > work in detail but thats what came to my tired mind on early monday > morning :)
Varnish uses (and likes) keep-alive to the back-end. You want your backend to support keep-alive, since there's little point in re-establishing connections all the time. There's a "backend connections reused" counter that'll tell indicate how efficient Varnish is at taking advantage of keep-alive (and recycled, which is much the same thing). There's one exception, though: When you are using pipe (not pass), you want to set "connection: close" in vcl_pipe to disable keep-alive. This is because Varnish only sees the first request in a piped session - if the first request is piped, the next requests will be too. This is a problem if you need different backends for the requests; have cached the subsequent requests; or if you need the x-forwarded-for header or other varnish-manipulated headers on the subsequent requests. But other than pipe, you really want to use keep-alive. - Kristian
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