Re: Webserver Redundacy
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You may want to have a look at this
"Some desktop clients may even try alternate addresses after a
connection time out of 30-45 seconds."
It looks like you are correct, and some browsers seem to implement
their round robin
dns like this.
This behavior is unfortunately not specified - and could be changed
at any time.
On 28/02/2007, at 4:54 PM, Jim Popovitch wrote:
If this is the case, then you may also have a session persistence
:-) I thought you said that we would have a 50% loss problem. Are you
just grasping for straws? :-)
The problem is that there is no specification on how to deal with
IP addresses for the one host.
A) Do you swap IPs every request?
B) Do you stay with the one IP till end of session?
C) Do you stay with the one IP for 30 minutes?
D) Do you change IP when you get a 'no able to connect'?
As it seems, at the moment, IEs implementation seems to solve your
If the browser switches IP addresses between queries, the other web
server may be asked to respond, in which case, you will not be
able to store
state in the web server, and will need to store it in the backend
this between requests - not visits.
Yes. But you assume that state is necessary to maintain. It may not
be. My experience has shown me that browsers don't switch IP
between queries, they use the first one that works and they keep using
it as long as it works. When it quits working they try the next
Quoting one of the links above
Microsoft's Internet Explorer caches the results of domain name
lookups internally, retaining the results of previous lookups for 30
minutes by default (which can be modified by adjusting the
DnsCacheTimeout value of the HKEY_CURRENT_USER\Software\Microsoft
\Windows\CurrentVersion\Internet Settings key in the Windows
registry). This caching occurs separately within each Internet
Explorer process, but an individual Internet Explorer process may be
responsible for several web browser windows.
If you assume that you don't need to deal with session persistence
experience, you may end up getting bitten when someone changes the
behavior of <insert your favourite browser>.
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