Moving everything to a new machine.
WHAT TO PLAN FIRST
An inventory of what is on the old machine.
WHAT THAT INCLUDES
Sites and their files Databases Mail accounts and mail Certificates Scheduled tasks Configuration DNS records
WHAT IS MOST OFTEN FORGOTTEN
Cron jobs, and mail.
WHAT THE SEQUENCE IS
Build and configure the new machine Copy data Test against the new machine directly Reduce DNS record lifetimes in advance Do a final copy of anything that changed Switch DNS Keep the old machine running
HOW TO TEST BEFORE SWITCHING
Override the address locally, so only you reach the new server.
WHY REDUCE RECORD LIFETIMES FIRST
It shortens the window in which visitors are split between machines.
HOW LONG BEFORE
At least as long as the current lifetime.
WHAT TO DO ABOUT THE SPLIT PERIOD
Expect both machines to receive traffic, and plan for it.
WHY THAT MATTERS FOR DATABASES
Writes landing on the old machine after cutover are lost.
WHAT REDUCES THAT RISK
Making the old machine read-only, or redirecting it.
HOW LONG TO KEEP THE OLD SERVER
Until you are certain, which is longer than it feels.
WHAT TO CHECK AFTER
Mail delivery, which fails quietly.
