Cutovers and migrations of networks and systems still scare me after 15 years of being IT, there is an element of the unknown or undiscovered that always keeps me on my toes. I do have an approach which is relativity well known which can help IT infrastructure migration that is Discovery, Prep, Pre, Inflight, and Post Flight stages.
Discovery Phase - this consists of gathering as much information as possible about the network or system to be migrated. This is essentially the requirements phase, gathering information on the system and what is required to migrate it. This can be anything from talking to end users or systems owners, analyzing drawings, network flows or rules and understanding every element of the system or network so that no requirement is missed. This stage is probably the most critical and time consuming, but does help build the below steps.
Prep Phase – Once the discovery phase is completed, you should have a good handle on preparation work required for the migration, this can be building servers, network configs, installation of cabling or devices, talking to system owners and end users of possible impact to services during the migration and also writing up tests that will be used to validate the migration in the Pre and Post stages.
Pre-Flight Phase – This phase is executed anywhere from 24 hours to 20 minutes before the actual change, checking that the system is working as intended and that no faults are present by running the tests documented in the Prep Phase, this is to ensure that you are not chasing your tail in the post stage with any latent or existing faults. This can be also smaller tasks such as calling NOC or other IT teams of change, ensuring that prep tasks are completed and any or tasks pertinent to the Pre-Flight phase.
Inflight – Written in the Prep phase, this should be a playbook of tasks/steps for everyone involved in the migration, will also need to include PONR (Point Of No Return) if applicable, details on rollback procedures and any testing. If the migration is large, then setting timelines of tasks can help keep track of time and help deciding if a rollback is required.
Post Flight – This mainly consists of executing the same tests in the Prep Phase and ensuring that the functionally of the newly migrated system or network is working as intended. Include a summery email to all key stakeholders of the migration and organise a next business day team on standby to help with any issues that may arise if migration is at night.