Re: application based HA

My problem is a bit easier then you mentioned with the mail server 
example because I dont have many processes to check. The application is 
handling well the active/passive state and I dont have to care about the 
data incosistency.
The problem comes from this situation. Both of the servers are alive and 
heartbeat (that doesnt support app level HA) is changing the IP address 
when the active server failed.

Andras


On 2014.11.15. 17:21, Miles Fidelman wrote:
> Andras POTOCZKY wrote:
>> Hi List,
>>
>> I would like to configure an application based HA solution. I mean if 
>> my important application stops working (but the active server is 
>> still alive), the HA configuration is passing the shared IP to the 
>> standby node.
>>
>> I've found pacemaker is the tool for it but I couldnt find any 
>> document or example related to the application level HA.
>>
>> Can somebody point me how can I figure this out?
>>
>>
>
> The short answer: Look for documentation on resource agents.  If your 
> application has a pre-existing resource agent defined, then you set 
> that up and it handles failover.
>
> The longer answer is that application-level failover is difficult, 
> because it involves things like:
> - IP addresses
> - process state
> - work queues
> - data files
> - etc.
> All of which are unique to a specific application.
>
> Hence, it becomes a lot easier to:
> - address failover at the virtual machine level (IP addresses, 
> applications, processes)
> - use either a storage area network, or DRBD to make sure that your 
> data remains available and consistent
>
> Some applications provide their own application-layer failover - such 
> as databases with replication logic built in:
> - put them behind a load leveler, and you're done (assuming your 
> load-leveler isn't a single point of failure), or,
> - if your public-facing DNS name points to multiple IP addresses, then 
> you have a level of failover there, or,
> - use CARP to support IP address failover
>
> For other applications, it's quite a bit harder:  I've been trying to 
> come up with a way to make our email and mailing-list infrastructure 
> HA, at the application layer, but there are so many distinct processes 
> running, and ques, and such, that just VM-level failover, with DRBD 
> disk replication has always been far simpler. (The reason I keep 
> looking is that I'd like to migrate to either a BSD or illumos based 
> platform, but there's no Xen and no DRBD.)
>
> Miles Fidelman
>
>
>
> HAST
> I've been wrestling with this one for a while - more in terms of 
> setting up HA applications
>
>

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