High Availability of a web server on a distributed cloud

[Digimer]

On 01/14/2013 09:33 AM, Jamon Camisso wrote:
> On 13-01-14 08:57 AM, Dave Cramer wrote:
>> It is relatively simple to distribute an application to a number of servers
>> and use haproxy to switch ip's. What I can't figure out is how to switch
>> make sure that the IP that points to ha-proxy can be moved easily if that
>> machine fails ?
> 
> Research things like pacemaker, heartbeat, stonith, and using 3 or more
> nodes in your system (3 nodes so that you don't end up in a split brain
> situation, especially if your systems are distributed).
> 
> You'll likely want another back-channel method of communicating between
> each system in case something goes awry - what if one your ISP/cloud
> providers can't route public traffic to a node, but the node still
> thinks it is online?
> 
> You want some method of achieving a quorum between remaining nodes, and
> some method of killing off the rogue node.

A few points;

- Heartbeat is deprecated, don't use it.
- Quorum is optional. Both pacemaker and cman/rgmanager (Red Hat) use
corosync for cluster communication and membership. Both can disable
quorum and this is fine.
- The members need to be (physically) close to each so that you can use
fencing. Fencing is critical to safe operation of a cluster. Without it,
it is easy/possible for a split-brain to occur.

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Digimer
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