Ok, here's a migration checklist of items you should look at when setting up a new server to take the place of an old one:
Date and Time, NTP anyone?
ntp.html - Let's hope you're using something like ntp. Otherwise, at least set it up to some realistic value. Hey even having it run ntpdate once a night is better than not at all.
Hostname
hostname.html - You have to set the hostname (hostname, DDNS, WINS) up right for everything else to work right -- remember not to have both systems on the network with the same name at the same time, duh!!
IP Addressing - Static / DHCP - Name resolution: DNS, DDNS, WINS?
Check all network interfaces in the old system and see if they have static IP addresses or are using DHCP to get their addresses. Also don't forget about adding the default gateway and any other static routes if not using any dhcp interfaces.static-routes.html
Services
What services will you be running on the new system: http, ftp, nfs, smb, dns (bind/named), dhcp, cvs, .... Identify services with lots of data to be transferred. Also identify which services must be running until the last minute and which ones can be taken offline sooner. Make a timetable of what can be taken offline and transferred when.
Generally for small services (services with not much data) can be transferred to the new system at time of migration. For larger services (services with considerable amounts of data) will take a long time to transfer to the new system and so it must be decided how to best move these large services. If the large service can be taken offline for a long time then that service can start transferring its files files to the new server once such service is taken offline. If a large service cannot be taken down for a long period of time then rsync may be used to perform synchronizations to the new system prior to taking the service offline -- see the section titled "Services with Large Data to be transferred" for more details.
It is best not to perform a backup of any service while that service is running. You should always take a service offline and then perform the backup due to the fact that the data files may not be consistant while the service is running. Some services may have special tools for performing a backup while that service is running, not many do.
Services with Large Data to be transferred
If a service has a large amount of data to be transferred to the new system, you have a couple of choices:
Schedule to take the service offline, take the service down permanently on the old system, perform the transfer, bring the service back up when you restart the new system.
Another option is to use something like "rsync" to get the bulk of the data to the new system. rsync can tell if a file's contents have changed or not and only sends what has changed in each file. Using rsync you could leave a large service up until the last minute (running rsync every so often to keep up to date), then do a final rsync after you take the service down permanently on the old system and before starting it on the new system. Remember not to do any more rsyncs from the old system to the new system after you bring up the service on the new system! Duh!
Backups
Don't forget to backup /home, /root, /etc, and any other special files you may need.
Speed of Transferring Data - Use your time wisely
Make sure you have the fastest possible connection between the two systems, i.e. 100MBit vs. 10MBit transfer speeds.
Use fast commands to backup, transfer, and unpack your data. Try to do all 3 procedures simultaneously rather than sequentially:
(cd / && tar -czf - home/) | ssh root@new_system "(cd / && tar -xzvf -)" sshcopy.html
Notifications
Be sure to give ample notice to the users of what will happen when.
Setting up services on new server
You should set up the services on the new server as soon as possible with the exception of dhcp and dns, just make sure these are installed if you will be using them. Try to get configuration files in place for your services as soon as possible to make sure they are performing as expected.
Shutdown Procedure
Work out a shutdown procedure / timetable:
Set up services on new server, transfer necessary configration files from old system.
Services that will be taken down 4 hours before migration
Transfer of these services to new system, service is left off until brought up on new system.
Migration Begins:
final services are taken offline (service named stop; service dhcpd stop; ...)
transfer of these services (data files) to the new server
transfer of dhcpd configuration file to new server if you haven't transferred it yet:
(cd /etc && tar -czf - dhcpd.conf) | ssh root@new_server "(cd /etc && tar -xzvf -)"
transfer of dhcpd data files if you will be running dhchd:
(cd /var/lib && tar -czf - dhcp/) | ssh root@new_server "(cd /var/lib && tar -xzvf -)"
transfer of named configuration file to new server if you haven't transferred it yet:
(cd /etc && tar -czf - named.conf) | ssh root@new_server "(cd /etc && tar -xzvf -)"
transfer of named data files if you will be running named:
(cd /var && tar -czf - named/) | ssh root@new_server "(cd /var && tar -xzvf -)"
final rsyncs for any large services
change hostname of old server - hostname.html
change ip address(es) of old server if necessary (for static ip's)
change ip address(es) of new server if necessary (static ip's)
change hostname of new server - hostname.html
make sure you route table is looking good.
bring up all your services (service named start; service dhcpd start)
make sure your services will start at boot time (chkconfig --list my_service)
check all services to make sure everything looks good
make sure users can log in
Once all the services look good then give the all clear to the users
If you have any corrections, cleanup, or additions to this please contact me.
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