[Linux-HA] Can linux-ha manage a dual-uplink scenario

[Dirk Jagdmann]

Hello,

I'd like to make a server fault tolerant by using two computers and 
provide some failover if one of them fails. As the servers need to 
communicate with other clients and server with the network I have to 
deal with the issue, that the network (and not my server) fails. However 
I'd like to do a server failover only, when the server itself (and not 
the connecting network) goes out of service, because the server contains 
complex databases were failover is not trivial. My servers are embedded 
in a collection of other servers and existing network infrastructure, 
which is basically already built redundantly.

+---------+                           +---------+
|Server A1|+------+           +------+|Server A2|
+---------+       |           |       +---------+
                   |           |
+---------+       |           |       +---------+
|Server B1|+---+  |           |  +---+|Server B2|
+---------+    |  |           |  |    +---------+
               +-------+   +-------+
               |Switch1|+-+|Switch2|
               +-------+   +-------+
                |    |       |    |
             +--+    |       |    |
             |       +----------+ |
             |  +------------+  | |
             |  |               | |
           1a|  |1b           2a| |2b
         +----------+       +----------+
         |My Server1|       |My Server2|
         +----------+       +----------+

Server A1 and A2 both provide the same functionality, the same with B1 
and B2. So if either A1 or Switch1 fails my servers 1 and 2 can still 
reach A2. The High Availabilty restriction of this project is, that one 
component (either server or network [network includes the cable as 
well]) may fail. If two components fails simultaneously the project may 
suffer from (partial) failure.

What I'd like to accomplish is, that if MyServer1 is currently active 
and Switch1 fails, I'd like to stay on MyServer1 and continue execution 
with ServerA2 and ServerB2 via Switch2. Further I have to avoid a 
Multi-Master (or Multi-Active) Situation, so my Servers 1 and 2 have to 
communicate and detect wheter they are both alive and then decide on a 
master node.

What I'd like to have is a configuration/software that runs on MyServer1 
and MyServer2 and detects which Servers a alive, then decide which 
server should be active/master. Then on the active server a shared IP 
address is configured for on is its interfaces (a or b). If the software 
detects a network failure on the configured interface it should switch 
the IP address to the other interface.

Can this be done with the current linux-ha components? Or would this 
require some enhancements to certain parts of linux-ha?

-- 
---> Dirk Jagdmann ^ doj / cubic
----> http://cubic.org/~doj
-----> http://llg.cubic.org