On 3 June 2013 22:36, Ali Majdzadeh <[email protected]> wrote: > > Hello All, > I am totally new to HAProxy. What I am looking for is a solution for HTTP > load balancing and according to what I have read about HAProxy, I think this > is the right choice.
Hi Ali. I've found HAProxy to be a really good HTTP load-balancer. Here's my unofficial take on your questions. > Concerning HTTP, HAProxy is session-aware. Does this mean that all the > requests initiated from a specific client goes only to a specific back-end > server? This can be configured, yes. > What happens if suddenly the back-end server fails? Your backend should expose a health check URI that can be requested by HAProxy frequently (very frequently, if possible). If it stops returning a 200, then that backend will stop receiving new requests. The details of this are all configurable - timeouts, number of failed health checks required to fail a backend, etc. > For example, suppose that a user is downloading a file from a back-end web > server and the same file exists on another back-end web server. The load on > these two servers is balanced by HAProxy. Now, what happens if the first web > server dies whilst the file is being downloaded? The client will receive an incomplete download. This is unavoidable - any solution mitigating this would have to be highly coupled to the backend service being provided, as a generic solution would almost certainly not be HTTP RFC compliant. > Does the download continues from the second server from where it was > interrupted? No. Another request will need to be made, through HAProxy (and not /by/ HAProxy) to the backend. > I am not sure whether I have got the correct understanding of > session-awareness feature in HAProxy. I do appreciate your comments. I don't think that HAProxy's sessions are related to the kind of in-request failure you seem to be concerned about. But I haven't run the current 1.5 development version, so I may be out of touch with what it does in this area. Regards, Jonathan -- Jonathan Matthews // Oxford, London, UK http://www.jpluscplusm.com/contact.html
