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> On Tuesday, January 09, 2007 Joseph Mack NA3T wrote:
> On Mon, 8 Jan 2007, Dan Brown wrote:
>
> > I am looking at setting up a geographically separated set
> of directors
> > to perform failover with a pair of routers.
>
> You seem to be worried about IP blocks. You haven't let us
> know how you're going to detect failure and do the failover.
Well there's the problem I see with this. The farther away the directors
are from each other, the greater the chance of failover processes occuring
when they should not be. Other than a rather large timeout, I could setup
something like a self re-establishing modem connection to pass connection
data back and forth and provide secondary heartbeat.
> When both directors are side by side, you assume that the
> networking won't fail. When the directors are geographically
> separate, are you failing out because of network failure (OK,
> if so how are you going to detect failure) or node failure
> (poor use of failover, since you can't assume the network
> between the two nodes is up).
Well, using node failure would be a primary trigger, and I'd have to build
in some other counter measures such as route checking (eg. seeing if the
last route between the servers is still up). This is also a poor method of
checking failover since routes can change, but on a usually stable network
where network paths don't cross outside of the ISPs network it may be a
satisfactory (not acceptable mind you, just borderline) method if routes are
updated every couple of minutes.
> Once you've detected failure, do you have a plan for moving
> the IPs to the backup site?
This is the thing I am unsure about. If trying to do this on the same
network, can I simply have a director assume the router IP and the block of
IPs and have it be on it's merry way? I noticed your comment to Howard Chen
shortly after I sent my own message. All of the solutions for
geographically distant failover/balancing seem to have either access to the
network's DNS, or require setting up BGP.
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Dan Brown
danb@xxxxxx
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