Sybase servers on the the move

[Wim Van den Wyngaert]

We have an interbuilding cluster within an international network (worldwide, ING bank).

We have a number of Sybase servers that we want to move from one node of the cluster to another, and back. Problem is that the IP address changes and that some PC clients must be modified to let them follow the change.

In a 2nd phase I want to be able to move the server to any place in the network (t.i. worldwide). All without modifying clients (pc's).

What is the best solution to do this ? IP aliases ? DNS ? Who has something operational ?

Wim

[Jan van den Ende]

Wim,

we have kind of a superset of your demand.

- ANY application has an associated DNS name.
This DNS name is a CNAME of a nodename, or a round-robin of such CNAMES.
For this purpose, special communications programs etc are also considered "applications" (athough not user-accessable)
The nodenames themselves have the IP addresses.

ALL users access ANY VMS application ONLY by that service name.

Now, all we need to do to move an applic, (or change the set of nodes on which it runs) is change the CNAME.

If you start in time (too late now, I fear) than you can essentially move or redistribute any time that suits you.

Proost.

Have one on me.

jpe

[Wim Van den Wyngaert]

Jan,

I have only basic DNS knowledge.

Where do you change the CNAME ?

Is DNS capable of detecting that Sybase is on node1 and not on node2 but after a problem (or crash or manual operation) is on node2 but not node1 (so called companion) ?

Wim

[Kris Clippeleyr]

Wim,

Over here we have defined in our DNS a hostname/ip-address for every application known.
At application startup, a special command procedure is run that
1. checks the existence on the network of the correponding hostname/ip-address, thus preventing an application from starting twice on different systems (application here are bound to 1 VMS system).
2. if the host/ip-address cannot be found, "aliases" one of the network cards of the system with the application's ip-address. Something like:
ifconfig we0 alias w.x.y.z/n (where n=number of 1 bits in network mask)

Hope this helps,
Kris (aka Qkcl)

[Wim Van den Wyngaert]

Kris,

Both our buildings are in a different network (IP network part is different). How can routing be done without configuring the routers worldwide for this case ?

Wim

[Ian Miller.]

A CNAME is an alias or 2nd name for something. I think what Jan is doing is each application has a name which is used to connect to that application. The DNS server is updated to assign the names to whichever server or servers that application is running. When an application is moved the DNS server is updated so that name is now assigned the new server. This approach works as long as users and applications always use the name and look up the name often enough to pick up changes.

[Wim Van den Wyngaert]

Ian,

So, does it detect which node is running the application (via ping/port=) or does it simply give one of the node addresses to the client pc that connects and fails.

And I'm sure that it's not 1 DNS server for the worldwide ING bank, but I may be wrong.

Wim

[Ian Miller.]

I suspect its manual - a person knows on which server the application is running and sets the name in the DNS server accordingly.

Trying to do this automagically could be an entertaining excersise best left to someone else :-)

How often will the application move?

[Wim Van den Wyngaert]

Ian, of no importance how many times it moves (probably 2 times a year). I would like to define it once and once every time the list of machines changes.

Wim

[Willem Grooters]

No matter what method - if you named your databases, there must be a link between name and IP address that needs a change when a server moves, and that requires either automatic or manual action.
Multiple references in DNS is no option since that will use the first occurrence - no matter whether the node is alive or not.
Where multiple DNS servers are active, a change in one server may take time to be propageted over the network, which is another thing to take in account.

I guess the nodes are in the same network - if the nodes have multiple NICs you could think of failsafe-IP, and move the IP address with the Sybase server. You might be able to do so without Failsafe_ip, by chnaging the IP address of a NIC. I think you have time enough to do so when moving the database (just a minute, if you create a commandprocedure to take care of that).

You wouldn't need to do ANYTHING in DNS, in that case; you may need to flush ARP translatio tables, but that could be a gratuity of the TCPIP ipconfig command.

Willem