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Round Robin DNS

Discussion in 'Bind / DNS / Nameserver Issues' started by itf, Aug 22, 2002.

  1. itf

    itf Well-Known Member

    May 9, 2002
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    [quote:edb49a1f2e][i:edb49a1f2e]Originally posted by thaphantom[/i:edb49a1f2e]

    What s the best way to setup round robin dns in cpanel?[/quote:edb49a1f2e]
    [b:edb49a1f2e]Round Robin DNS is useful while you have a site with high-traffic and want to distribute this traffic between multiple servers[/b:edb49a1f2e]

    You have to configure Round Robin manually

    [b:edb49a1f2e]How to setup BIND for Round Robin DNS?[/b:edb49a1f2e]
    Enter multiple A records for the same host name pointing to different IP addresses in the primary zone file for the relevant domain like this:

    [b:edb49a1f2e]www 14400 IN A[/b:edb49a1f2e]

    To share the server load using a two-thirds to one-third ratio, enter one IP address on the list twice (2X) and a second IP address just once.
    Like this:

    [b:edb49a1f2e]www 14400 IN A[/b:edb49a1f2e]

    You have to configure httpd.conf on all of the machines (servers) for that domain and its relevant [b:edb49a1f2e] unique IP addresses [/b:edb49a1f2e] for each server. (It is recommended to setup them manually in each server)

    [b:edb49a1f2e]Cpanel powered servers:[/b:edb49a1f2e] Add your username and domain to your servers,(in WHM use Account Functions -& Create a New Account) then modify httpd.conf, proftpd.conf and DNS records manually. It is not recommended to setup Round Robin for email servers in the Cpanel.

    [b:edb49a1f2e]Round Robin for email Servers[/b:edb49a1f2e]
    For multiple email servers you can enter multiple MX records redirecting to different machines (servers), also you have to run mail transfer agent on each machine and configure them to receive emails and pass them to the users’ local mailbox or POP/IMAP mailbox.

    [b:edb49a1f2e]Round robin capability[/b:edb49a1f2e]
    If you have multiple servers with unique IP addresses, consider taking advantage of the round robin capabilities of IP profiles. Round robin configuration refers to a list of IP addresses that are assigned to a domain or hostname. Requests for the domain or hostname are distributed equally among the IP addresses on the list. This increases the stability of your server network by sharing the load.

    [b:edb49a1f2e]Round Robin DNS vs. Load Balancing[/b:edb49a1f2e]
    Round Robin does share the load equally among servers, however, it is different from what is commonly termed &load balancing&. Load balancing distributes connection loads across multiple servers, giving preference to those servers with the least amount of congestion. In Round Robin, server distribution remains on a rigid &one IP address to one user& rotating basis, but it still evenly distributes your server requests among your servers.

    [b:edb49a1f2e]Round Robin DNS Advantages and Disadvantages[/b:edb49a1f2e]
    One of the prime advantages of using Round Robin DNS is being able to take one of the server systems &out of the loop& for maintenance. Removing one of the entries on the list will have no effect on your visitors.

    However, be aware that if one system on your server list fails, it will appear to the user as intermittent failure because they will connect to the inactive server only a portion of the time.
  2. itf

    itf Well-Known Member

    May 9, 2002
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    [quote:6de7a77d9c][i:6de7a77d9c]Originally posted by thaphantom[/i:6de7a77d9c]

    thanks for your in depth help :)
    What I am doing is setting up IRC redirection
    I followed your instruction for the DNS, but it will only goto the 1st IP, why is this?[/quote:6de7a77d9c]
    Let me assure you that the instruction is OK but there are some notices about Round Robin DNS, I’ll write some of them here:

    [b:6de7a77d9c]Why Round Robin does not work in some systems effectively?[/b:6de7a77d9c]

    1) Round Robin is not effective for low traffic sites means you can’t make sure that it effectively works with a few visitors, because the first visitor will be forwarded to the server one the second to server two and the third to server three the fourth to the server 1 and like this.
    If you have a few visitors this logic would not effectively works

    2) There are something that cause Round Robin doesn’t work effectively, i.e. visitors enter your address like then it resolves to an IP address then this address is cached in their local system and when they retry that URL because they don’t use your DNS and use their local cached address instead; to access your site thus Round Robin doesn’t work, in brief Round Robin works while they attempt to use your DNS at each resolve
    It means if you would like to see Round Robin’s results you have to monitor your substantial visitors in a week (or a month)

    3) Round Robin doesn’t work if visitors use IP address instead of domain names (FQDN)

    4) Some services can not work with Round Robin due to their client side. i.e. Telephony, (IRC is 50-50 depends on the client side)

    5) Also for high-traffic sites if you don't configure cooperating DNS servers to support DNS load balancing, they could take only the first IP address returned from the initial lookup and use that for their client requests. Imagine a partner corporation with thousands of employees all pinned to a single server in your cluster!

    [b:6de7a77d9c]How did you check out your settings and make sure it doesn't work?[/b:6de7a77d9c]
    When a user receives an IP address, it is cached on the browser. Once the cache expires, the user makes another request for the IP address associated with a logical name. That second request can return the IP address of any other machine in the cluster, resulting in a lost session.

    Many corporations' and ISPs' DNS servers cache DNS lookups from their clients. Even if your DNS list of servers in the cluster could change dynamically, it would take time for the cached entries on other DNS servers to expire. For example, after a downed server is removed from your cluster's DNS list, AOL clients could still attempt to hit the downed server if AOL's DNS servers cached entries to the downed server. As a result, AOL users would not be able to connect to your site even if other machines in the cluster were available.
  3. TheCrazyHostGuy

    Apr 21, 2003
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    Round robin still seems to be the "old" method to balance the load on servers....

    Is there an effective method to balance the load with Cpanel?

    we would like to see about 3 servers handling the load for our customers that are using Cpanel.

    Out of the gates I see a few "sticking points" or concerns:

    1. when a customer makes changes to one server, what happens to cpanel in another server?

    2. what server does the customer upload their site to?

    3. What server is actually doing DNS..???

    4. What about e-mail..?? what server is getting it.. and how do you keep it in sync???

    With the discussions on round robin DNS I assumed this would be a good place to post this since I think we are all trying to achieve the same thing.

    Any suggestions would be great!



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