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Thread: Mock server redundancy

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    Funking Prink! Raz316's Avatar
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    Mock server redundancy

    For testing purposes, let's say using Ubuntu 8.10 Desktop can I do something like the following?

    I have two servers, Master and Slave.

    When a server boots its assigned the IP address 192.168.0.1.
    The server then pings 192.168.0.2.
    If there is no reply it changes its IP address to 192.168.0.2
    If there is a reply, it changes its IP address to 192.168.0.3

    Now when a server has booted and its IP address is 192.168.0.3 it pings 192.168.0.2 every minute to see if it's available.
    If it is, it does nothing.
    If it isn't it changes its IP address to 192.168.0.2 and send a warning message to me.

    Is that possible? Is there any reason why I shouldn't do the above? Per chance there is clash and an IP address conflict occurs, can I force the Slave server to go to 192.168.0.3.

    Thanks

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    Jay
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    Re: Mock server redundancy

    This can be done but not as you explain above.

    What needs to happen is you need domain replication with an alterate DNS
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  3. #3
    Splash
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    Re: Mock server redundancy

    I believe Ubuntu ships with Heartbeat - take a look at http://linux-ha.org/ which should give you an idea how to achieve what you're doing.

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    Re: Mock server redundancy

    What services are you trying to cluster ?

    I'm not sure how this would be implemented in linux , but from a Microsoft Perspective, each cluster node has its own (fixed ) IP. You would then have a floating virtual IP which the service would be bound to - the servers would make use of a secondary network connection between them known as the heartbeat to decide which server would respond on that virtual IP.
    my Virtualisation Blog http://jfvi.co.uk Virtualisation Podcast http://vsoup.net

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    Jay
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    Re: Mock server redundancy

    With Linux you can use Heartbeat but I have no idea how you would get it to do what you are asking and changing IPs in such a way as above may not be the best way to do things.

    Can you explain exactly why you want to cluster?
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    Re: Mock server redundancy

    Quote Originally Posted by Jay View Post
    This can be done but not as you explain above.

    What needs to happen is you need domain replication with an alterate DNS
    the DNS updates would be messy. clustering with virtual IP's and names would be a lot neater.
    my Virtualisation Blog http://jfvi.co.uk Virtualisation Podcast http://vsoup.net

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    Jay
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    Re: Mock server redundancy

    Quote Originally Posted by Moby-Dick View Post
    the DNS updates would be messy. clustering with virtual IP's and names would be a lot neater.
    yes, I agree after I had thought about it and also thought about clustering.
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    Funking Prink! Raz316's Avatar
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    Re: Mock server redundancy

    Wow, quick responses, thanks everyone

    I'll give heartbeat a look, it sounds like what I want (along with this O'Reilly document - http://www.onlamp.com/pub/a/onlamp/2...inuxhacks.html ).

    The machines will be running a web server (with the Slave doing live replication of the Master mysql database and a daily rsync of the htdocs directory). On writing that though, I've just realised that I need to keep the same IP address on the slave machine for the mysql permissions. So again, this points to the virtual IP set up.

    In our current set up we will only be allowed two boxes and do not have access to the DNS to allow for any redundancy there (unless I am missing something?).

  9. #9
    Splash
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    Re: Mock server redundancy

    Heartbeat *shouldn't* (though I've never used it myself, so take this with a pinch of salt) rely on DNS, so long as you have a heartbeat connection between the cluster nodes.

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    Re: Mock server redundancy

    heartbeat doesn't need DNS as it a direct connection between the two servers.
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    Re: Mock server redundancy

    Quote Originally Posted by Splash View Post
    I believe Ubuntu ships with Heartbeat - take a look at http://linux-ha.org/ which should give you an idea how to achieve what you're doing.
    Spot on, that's the tool to use

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    Re: Mock server redundancy

    Ahh Hexus - 'Operating systems & applications' you've been good to me over many years.

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    Re: Mock server redundancy

    typically HA can (and should) run over multiple links, in case the link fails but the servers are fine - fr'example, we have a storage system where the two machines are directly connected over serial, but also directly connected over ethernet, but also connected via fibre ethernet on some switches

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