[Pacemaker] Multinode cluster question

[Andreas Kurz]

On 11/08/2011 12:02 PM, Attila Megyeri wrote:
> Hi All,
> 
>  
> 
> I need some help/guidance, on how to make sure that certain resources
> (running in virtual cluster nodes) are run on the same physical server.
> 
>  
> 
> The setup:
> 
>  
> 
> I have a cluster made of two physical nodes, that I am willing to use
> for HA purposes (no LB for the time being).
> 
> I have a failover IPfrom the provider, that is controlled using a
> resource agent from one pair of the virtual machines(web1 and web2), and
> the IP is assigned always to one of the physical servers.
> 
> On the physical server I use iptables pre/postrouting to direct the
> traffic to the appropriate virtual node.The routing points to the web
> VIP, and red5 VIP.
> 
>  
> 
> On the physical servers I have 3-3 virtual servers, that host the
> specific roles of the solution, e.g. db1 db2, web1 web2, red5_1 red5_2.
> 
> The virtual servers use the default gateway of their own physical server
> to talk to the outside world.
> 
>  
> 
> My first idea was to create 3 independent two-node clusters. Db cluster,
> web cluster, red5 cluster.
> 
> The db cluster is a M/S psql, with a virtual IP.
> 
> The web cluster is an apache2 cluster, cloned on two virtual servers,
> with a failover IP RA (if node1 on phy1 fails, failover Ip is redirected
> to phy2 and vice versa).
> 
> Red5 is a red5 cluster running on two instances, with a virtual IP
> (internal).
> 
>  
> 
> This is where it gets interesting – because of the default gateway.
> 
> The db cluster is accessed from the intranet only – no worries here.
> 
>  
> 
> Red5 is different – but it needs further explanation.
> 
> Let’s assume that all roles (db master, web, red5) are running on
> phisical server  1.
> 
> Web1 fails for some reason. Web2 role will become active, and the
> external failover IP will point from now on to physical node2.  The
> iptables script still points to the same VIP address, but it now runs on
> a different node. No issue shere, as Web2  gets its traffic properly, as
> it KNOWs that it is running on node2 now.
> 
>  
> 
> The issue is with Red5.
> 
> Red5 runs on node1, and uses default gw on node1. [it does not know that
> the external failover IP no longer points to node1].
> 
> When a request is received on the failover IP (now ph node2), iptables
> redirects it to red5’s VIP. Red5, running on node1 gets this request,
> but does not know that it shall be routed through node2!
> 
> As such, the replies, will be routed through ph node1 – as it is the
> default gw. This is definitively not the right approach.
> 
>  
> 
> The actual question is:
> 
> -          Should I treat all nodes inside the same cluster (db1, db2,
> web1, web2, red1, red2) – and this way I could possibly detect that
> failover IP has changed and I should “do something” with red5?
> 
> -          “Do something” could mean for me one of the following:
> 
> o   If “web” VIP is running on physical node 2 (on node “web2”), then
> move “red” VIP to physical node2 (to node “red2”)
> 
> o   Alternatively, only change the default gateway for red1, to use
> “node2” as the default gateway?

Why not doing all traffic between the VMs via an internal net only ...
e.g. a direct connnected nic between hosts, bridged and all VMs
connected to it?

Regards,
Andreas

-- 
Need help with Pacemaker?
http://www.hastexo.com/now

> 
>  
> 
> I hope my question is clear, and that the setup mentioned here is quite
> common.
> 
> I am asking the experts, what is the recommended approach in this case.
> 
>  
> 
>  
> 
> Thank you in advance,
> 
>  
> 
> Attila
> 
>  
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> 
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