A critical decision to make early during planning, is an IP addressing strategy for workloads to be moved. This comes down to a decision between two possible scenarios.
Scenario 1: Workloads change their IP addresses
In the case where workloads will change their IP addresses, there are certain additional planning activities to be performed.
A new IP addressing scheme must be determined for the migrated workloads.
Application owners must be made aware of the new IP addressing schemes and must be prepared to update their applications accordingly.
System administrators must make plans for changing workload IP addresses post-migration.
Updates to DNS, Firewalls, Load Balancers, Certificates, and other infrastructure services must be coordinated to reflect changes in IP assignments.
Scenario 2: Workloads keep their existing IP addresses
A common goal of a migration project is to minimize disruption to business. However, IP address changes tend to be very disruptive. For this reason, most migration projects will require that workloads keep their IP addresses post-migration.
In order to accomplish this, there are two choices:
Migrate entire subnets worth of workloads at a time.
Utilize a layer-2 network extension during the migration.
Since workloads that house applications aren’t always arranged neatly within the bounds of a given subnet, it is often impractical to plan migrations around subnet boundaries. For this reason, the most common strategy is to utilize a Layer 2 network extension during a migration. Network extensions provide a great deal of flexibility in how a migration is performed and allow entire applications to be migrated regardless of the layout of the underlying network addressing scheme.