"Butter, Frank" <Frank.Butter@otto.de>:
> we need a simple cluster solution for safe ftp.
> that means one single ip-address known to clients and
> two/multiple physical machines behind it as ftp-server.
> it should be fail-safe so that switching off one machine
> doesn't affect the clients.
>
> any suggestions?
How about one of the following:
A. Manual host selection method
1. DNS does the normal round robin broadcast of N IP numbers.
2. Each server has a primary IP - (one from the list of N)
3. Each server has the capability of a second IP number.
When it becomes time to take a system down:
1. assign the real IP number to one of the other servers
2. down the network interface on the host being removed.
Work on the down system using a test IP number (not one of N addresses).
When it is tme to bring it back on-line:
1. remove the IP from the secondary
2. bring up the server with the proper IP address (one of the N).
B. Router assisted automatic method:
It isn't an "automatic" failover, but depending on N, and a router/switch
it could be:
1. Each server has a primary address (one of N)
2. Each server as secondary addresses reached only via routing from the primary
address as specified in the host IP configuration.
There is a single step to down a particular system:
1. The router/switch is directed to send the "down" systems IP to another
server as the "best route to" that IP. This allows the IP to be redirected to
one of (N-1) systems.
Bringing a system up should also be a one-step - the router/switch is directed
to stop redirecting.
The target system will be doing double duty for a while since it's effective
IP number would show up twice as often as any other.
Technique B requires more hardware (and what happens when the router/switch
fails...) but is the cleanest method for a "single step" procedure.
I haven't done this, but it is my understanding that the router method has
been done elsewhere.
-------------------------------------------------------------------------
Jesse I Pollard, II
Email: pollard@navo.hpc.mil
Any opinions expressed are solely my own.
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