Re: Web Services DNS Round Robin
- From: "Nick Malik [Microsoft]" <nickmalik@xxxxxxxxxxxxxxxxxx>
- Date: Tue, 3 May 2005 06:29:08 -0700
sure. So would any software load balancing scheme and you wouldn't need the
F5. Microsoft has a good software load balancing solution you may want to
consider.
--
--- Nick Malik [Microsoft]
MCSD, CFPS, Certified Scrummaster
http://blogs.msdn.com/nickmalik
Disclaimer: Opinions expressed in this forum are my own, and not
representative of my employer.
I do not answer questions on behalf of my employer. I'm just a
programmer helping programmers.
--
"JP" <JpMaxMan@xxxxxxxxx> wrote in message
news:enABPwcTFHA.3176@xxxxxxxxxxxxxxxxxxxxxxx
> Ok - I understand your concern. That's interesting about the "closest" IP
> , wasn't aware of that.
>
> One final question on this - what if this is just to load balance 2
> servers purely for redundancy purposes. That is, either server could
> easily handle all the traffic. In this scenario, it seems like the DNS
> load blaancing in a server to server model would be fine?
>
> "Nick Malik [Microsoft]" <nickmalik@xxxxxxxxxxxxxxxxxx> wrote in message
> news:15SdnY-tsuqZfe7fRVn-ow@xxxxxxxxxxxxxx
>> this won't work when connecting a server to a server in your network.
>> This is used to allow a DNS Cache to choose who to call. Certainly the
>> DNS cache for a client machine is managed by the client. For your
>> server, though, once a client server gets the IP address of the app
>> server, it will keep using it until the IP dies. This is very very bad.
>> You defeat the purpose of load balancing altogether.
>>
>> F5 offers this as an option if you have to distribute a single web site
>> to servers around the world. DNS Cache servers at various ISPs can be
>> configured to return the "closest" IP address, so this allows the ISP to
>> present Amazon.uk to customers in England, and Amazon.com to customers in
>> the US. Unless you plan to multiply distribute your web service app
>> servers around the globe, and set up your client web servers under a
>> variety of ISP hosting sites, you probably shouldn't consider this option
>> for use in a server-to-server configuration.
>>
>> --
>> --- Nick Malik [Microsoft]
>> MCSD, CFPS, Certified Scrummaster
>> http://blogs.msdn.com/nickmalik
>>
>> Disclaimer: Opinions expressed in this forum are my own, and not
>> representative of my employer.
>> I do not answer questions on behalf of my employer. I'm just a
>> programmer helping programmers.
>> --
>> "JP" <JpMaxMan@xxxxxxxxx> wrote in message
>> news:ebZHy5aTFHA.2560@xxxxxxxxxxxxxxxxxxxxxxx
>>> Right. I understand this method - and we have this segmented using
>>> VLAN's w/ a LB machine inbetwen holding the single IP w/ several
>>> machines behind it.
>>>
>>> What I was wondering is using a different model, DNS load balancing,
>>> where the decision comes from to decide which IP to pull. We use DJBDNS
>>> and this information seemed to indicate the client made the decision.
>>> However, in doing some ping tests on several machines it seems that it
>>> is actually handing out sequential IPs. Just not fmailiar with what is
>>> going on behind the scenes and wanted to make sure that when using ASP
>>> to pull a web service via HTTP the behavior would be the same.
>>>
>>> How to balance load among many web servers
>>> These instructions assume that you are already running tinydns, version
>>> 1.04 or later, as a DNS server.
>>> Suppose you have 50 identical www.heaven.af.mil web servers running on
>>> IP addresses 1.2.3.150, 1.2.3.151, and so on. You can simply list all
>>> their addresses in /service/tinydns/root/data:
>>>
>>> +www.heaven.af.mil:1.2.3.150
>>> +www.heaven.af.mil:1.2.3.151
>>> +www.heaven.af.mil:1.2.3.152
>>> # etc.
>>> When a DNS cache asks for the IP address of www.heaven.af.mil, tinydns
>>> will automatically return a random set of 8 addresses.
>>> If one of your web servers crashes, the effect on users will depend on
>>> how their browsers behave:
>>>
>>> a.. Silly behavior: I've heard rumors of obsolete browsers that give up
>>> after a single IP address.
>>> b.. Standard behavior: Most browsers move on to the next IP address
>>> after the first connection attempt times out. A server outage produces a
>>> long delay but not a failure.
>>> c.. Smart behavior: To reduce the delay, smart browsers try each
>>> address with a two-second timeout before retrying each address with a
>>> long timeout.
>>> You can eliminate delays by removing IP addresses of web servers that
>>> have crashed. tinydns is designed to work with external programs that
>>> monitor the health of your servers. Specify each address with a 5-second
>>> TTL:
>>>
>>> +www.heaven.af.mil:1.2.3.150:5
>>> +www.heaven.af.mil:1.2.3.151:5
>>> +www.heaven.af.mil:1.2.3.152:5
>>> An external program can remove an address by simply changing + to - on
>>> the relevant line, then running make. Later, when that server has
>>> recovered, the program can change - back to +.
>>>
>>>
>>> "Nick Malik [Microsoft]" <nickmalik@xxxxxxxxxxxxxxxxxx> wrote in message
>>> news:AL-dnWKb4oaAJ-7fRVn-uQ@xxxxxxxxxxxxxx
>>>> You are looking at the network from the side of the servers, not the
>>>> side of the clients.
>>>>
>>>> When you put in a NLB, you make one IP address visible. It is a
>>>> Virtual IP. The caller (in this case, your ASP site) cannot tell that
>>>> there are three machines under the covers. That machine (or farm?)
>>>> need to use the DNS entry assigned to the Virtual IP, not the contained
>>>> IP addresses.
>>>>
>>>> This is a bit confusing when you have all of the machines on a single
>>>> LAN. If it makes it less confusing, you can always configure a VLAN on
>>>> your switch to seperate the traffic from the ASP web server to your
>>>> NLB, and keep that apart from the traffic that flows from the NLB to
>>>> your web application servers.
>>>>
>>>> --
>>>> --- Nick Malik [Microsoft]
>>>> MCSD, CFPS, Certified Scrummaster
>>>> http://blogs.msdn.com/nickmalik
>>>>
>>>> Disclaimer: Opinions expressed in this forum are my own, and not
>>>> representative of my employer.
>>>> I do not answer questions on behalf of my employer. I'm just a
>>>> programmer helping programmers.
>>>> --
>>>> "JP" <JpMaxMan@xxxxxxxxx> wrote in message
>>>> news:uAI5FSaTFHA.1152@xxxxxxxxxxxxxxxxxxxxxxx
>>>>> Greetings - I have a classic ASP site that is accessing custom written
>>>>> .NET web services - we are looking at scalability options and though
>>>>> we have an F5 load balancer that would definitley do the trick, I was
>>>>> wondering how DNS load balancing was handled in such a situation?
>>>>>
>>>>> That is DNS Resolves:
>>>>>
>>>>> mywebservice.mydomain.com: 10.10.10.10, 10.10.10.11, 10.10.10.12
>>>>>
>>>>> I knwo most browsers will succesfully load balance this scenario, but
>>>>> it is up to the 'client' making the request.
>>>>>
>>>>> Any info would be appreciated.
>>>>>
>>>>> Thanks!
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>
>
.
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