Migrating to Another Linux

Gabriel2010 · 09-10-2004, 08:40 AM

Dear All,
Hope all is well.
Got a RHL8 box serving as a database server. Another system with just about the exact same settings but different IP address will be replacing it. These two nodes reside on an Active Directory Windows network & the first system has a static IP address. There;s a A host record for this system in the Active Directory DNS server.
In order for a succesful migration from one Linux to another and for the end user to be transparent to it all, how is it possible to automatically redirect connections from 1st Linux server to 2nd new Linux system?
I was thinking in regards to the 2ndLinuxServer, creating an A host record with respective name ( this should not matter) & assigning it the same IP address as the 1stLinuxnode, all this done in the Windows DNS server.
Modify the etc/hosts to reflect DNS servers interacting with the linux systems. Do the same with etc/resolv.conf
What do you guys think?
Thanks in advance (TIA)
Gabriel

hob · 09-11-2004, 06:42 PM

We did a similar migration last week, but with a mail server.

You can't get transparent failover without clustering etc. - existing connections will be terminated when the system goes offline. So it's really a case of reducing the period of unavailability to the minimum.

What we did was give the replacement box a different IP address for the commissioning process but give it the same IP and hostname when it went live. Since changes don't take effect until you restart networking you can change the settings of the replacement to the live configuration, shutdown the existing box and immediately restart the networking on the replacement to bring it into service.

So the downtime became the time taken to replicate any data from the old box to the new and reset permissions etc. (I wrote a small shell script to automate this bit), plus a minute to get the new box to the live network settings.

Any changes to DNS make the exact duration of service unavailability a bit uncertain because of caching and time delays on replication. By keeping the DNS record exactly the same you avoid the issue.