Migration Wave

A migration wave is a group of workloads and data coordinated through a migration plan. Google’s assessment guide distinguishes the order of waves from the order of workloads within each wave. A wave therefore need not be one simultaneous switch. Preparation, replication, testing, cutover, and stabilization may overlap other waves where dependencies and team capacity allow. The plan should specify which activities may overlap and which acceptance gates must finish first. AWS’s portfolio guide treats wave planning as iterative work, refined as application and infrastructure evidence improves.

Planning the intermediate states

Trace each dependency in both directions and describe what must work at each step. A dependency may move in the same wave, move earlier, stay in place, or be replaced. In every case, validate its interfaces, permissions, latency, and data meaning. Being in one wave does not make transitions atomic. The coexistence plan identifies authority and synchronization while paths overlap. In a fictional hospital, an undiscovered batch kept using an old pharmacy address and produced an empty bed view after the pharmacy moved. Owner consultation needed to lead to consumer tests, not just a notification. Gather the constraints, decisions, and cutover arrangements in a usable form, without requiring a fixed number of documents. Authorize execution using agreed evidence, such as reconciliation, access and performance tests, a recovery rehearsal, and explicit treatment of remaining risks. A planned wave and an approved move are different states.

Wave size and composition can change as the team learns. Google describes increasing batch size as one possible adjustment alongside changing order and membership. Greater experience does not make every later wave larger: a critical or tightly coupled workload may justify a smaller scope. Choose using potential failure impact, observability, recovery capacity, and available staff. Early candidate selection is explained in first mover. The assessment and strategy choices behind the plan are developed in The Inventory Said Two Hundred Systems and the Network Said Three Hundred and Forty.

References:

• Google Cloud Architecture Center, Migrate to Google Cloud: Assess and discover your workloads, last reviewed 2 August 2024 (CC BY 4.0).
• AWS Prescriptive Guidance, Application portfolio assessment guide for AWS Cloud migration.