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In 2023, there are few software projects that are true greenfield endeavors. Instead, migrations of existing systems are the new normal. Migrations done wrong can introduce substantial business and timeline risks into any software project. An incremental migration strategy can minimize those risks while pulling forward validation of business impact.

Vercel’s product is designed to support incremental migration from the ground up. In this post you'll get a high-level overview of incremental migration strategies and considerations.

Why migrate incrementally?

Almost all software projects that require migrations should aim for incremental migrations in order to:

• Minimize risk by reducing the scope of the individual steps of the migration.
• Minimize risk by having a more natural path to rolling back in the case of unexpected issues.
• Allow validating the technical implementation and business value substantially earlier in the process.
• Achieve downtime-free migration without maintenance windows.

Understanding big bang migrations

Big bang migrations are migrations in which a system is replaced in a one-time full switchover. There may be intermediate steps, but they are all performed in very short order. Basically, you pick a date, and on that date, all usage is moved from the legacy system to the new system.

Problems with big bang migrations can include:

You may go through the entire process only to learn that there are product problems that are very expensive to fix this late in the program. Rehearsals are inherently difficult to execute, making it hard to assess upfront whether a migration will succeed. You may reach a point of no return where a migration has to be completed even if major problems are noticed while it is happening. It may be required to take the legacy system offline while the migration is happening leading to lost business. Such maintenance windows often escalate in duration as issues are only discovered while the migration is running.