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question from scea@whizlabs

 
Timber Lee
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Your 3-tier application has been deployed in a production environment and has been running smoothly for over three months. However, recently you are getting three times the normal traffic due to a Television promotion campaign. To cope with increased traffic, you decided to introduce Round-Robin load balancing. Which of the following is the closest description about how the Round-Robin load balancing technique copes with the increased traffic?
I am confused, can Round-Robin perform load balancing? how about reverse proxy? please help me to understand, thanks
[ March 27, 2003: Message edited by: Timber Lee ]
 
Eduard Manas
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As I understand it (but again security is not my 'favourite' subject) a reverse proxy is the same as a normal proxy, but instead of monitoring outgoing traffic (ie from your network out) they monitor incoming traffic (ie from the outside in).
Having said that I don't see why reverse proxies cannot do load balancing by putting a little bit of intelligence in the proxy.
Eduard
 
Ian B Anderson
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Hello,
Reverse proxy load balancing
This is generally used when you have machines of varying capacity e.g. different CPUs and memory. You could have low spec. machines handling static requests and some high machines for SSL sessions � number crunching.
This helps you to make your solution use the available resources more efficiently.
The best source I have seen on load balancing can be found here:
http://www.engelschall.com/pw/wt/loadbalance/article.html
I have taken two paragraphs from this and pasted them below but I would recommend reading the whole document.
�We use a so-called Reverse Proxy, i.e. a HTTP Proxy Server operating in a direction which is reverse to the commonly known one. Usually a HTTP Proxy Server is logically used near the browsers or in front of them to bundle requests (when using a firewall) and to reduce bandwidth waste by performing data caching. Browsers call their proxy with the fully-qualified URL http://www.foo.dom/bar/quux/ and the proxy itself either forwards this request to parent proxies or finally requests the local URL /bar/quux/ from www.foo.dom. In other words, the proxy translates fully-qualified URLs either to fully-qualified URLs or local URLs. In contrast to this a Reverse Proxy masquerades as the final www.foo.dom server and translates the local URL back to a fully-qualified URL addressed to one of its backend servers.�

�Lets assume we have established this network/machine topology. What have we actually gained now? First we have a single point of access, the Reverse Proxy. This leads again to simplified traffic logging and monitoring of our website, although we are now using a webcluster instead of a single server. Secondly we now have complete control over the backend delegation scheme because its done locally in the Reverse Proxy for each request and not cached somewhere on the Internet. Additionally because the delegation scheme is now locally, a change of it immediately gets activated, for instance when one of the backend servers crash we just change the delegation configuration of the Reverse Proxy and the crashed backend no longer leads to errors for the visitors. After it is repaired we can activate it as simple as we deactivated it before.�
Round-robin load distribution:
Requests are sent evenly between servers, e.g. if there are 6 requests (r1, r2, r3, r4, r5, r6) and 3 servers (A, B, C) they will each handle two requests as shown below:
R1 � A
R2 � B
R3 � C
R4 � A
R5 � B
R6 � C
Note: This method of load distribution does not take account of the capacity of any of the servers, it assumes they are all equal. This is the simplest to implement.
Hope this helps.
Ian
[ March 28, 2003: Message edited by: Ian B Anderson ]
 
Timber Lee
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thanks
 
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