Migration from Traditional Infrastructure · Architecture as Code: the course

All courses / Architecture as Code / Module 4 / Chapter 16

Learning objectives

After the lesson the participant can:

Describe what a migration assessment must contain before a strategy is chosen.
Compare the four migration strategies and match each to a type of application.
Plan migration waves that balance technical dependencies with business priorities.
Explain why imported resources are checked for drift before any further change.

Key concepts

Migration assessment: The foundation of a migration: inventory of existing resources, dependency mapping, risk assessment that identifies critical systems, single points of failure and compliance dependencies, and cost-benefit analysis that informs strategy and timeline.
Lift-and-improve: A hybrid strategy that selectively re-architects critical components while keeping most unchanged. It balances speed with modernisation and suits phased, risk-balanced approaches and the majority of enterprise migrations.
Migration wave planning: Planning that balances technical dependencies with business priorities to minimise risk and maximise value. Pilot projects with non-critical systems enable team learning and process refinement before critical systems are migrated.
Gradual codification: Systematic conversion of existing resources to code management through import tooling, standardisation into reusable modules, reconciliation of existing configurations with the desired state, and Git-based tracking of progress with rollback.
Import followed by drift detection: The chapter's pattern for legacy import: a reviewed change set that neither creates nor deletes resources, followed by drift detection, so that the template is proven to describe reality before any further update touches the resources.

Interactive exercises

Do them here and get feedback at once. Choose a card and then where it belongs, or drag it.

Interactive exercise 1 · Sort

Which migration strategy fits

Sort each description into the migration strategy to which the chapter's table assigns it.

Interactive exercise 2 · Put in order

Importing legacy resources into code

Put the steps of the chapter's CloudFormation legacy import in order.

Teaching plan

15 min	Teacher presents the migration process from assessment to full adoption and the hybrid period in which legacy and code-managed resources coexist.
15 min	Sorting activity: participants receive short descriptions of applications and assign each to one of the four strategies, defending the choice with the table's criteria.
10 min	Teacher explains gradual codification, the import pattern and the transition of systems administrators and network engineers.
30 min	Exercise in groups: a wave plan for part of the participant's own estate.
5 min	Close with the summary: migration is a sequence of small, reversible steps, and it depends on organisational readiness.

Discussion

Lift-and-shift is the fastest route but brings limited cloud-native benefits. When is that trade-off the right one, according to the chapter's criteria?
What does a team learn from a pilot on a non-critical system that it could not learn from planning alone?
How would you support experienced systems administrators so that code-based workflows build on their knowledge instead of displacing it?

Written exercise

Exercise · 30 minutes

A migration wave plan

Take six to eight systems from your own organisation that are still configured by hand. For each, record its criticality, its main dependencies, any compliance dependency or downtime restriction, and its business value. Assign each system one of the four strategies: lift-and-shift, re-architecting, lift-and-improve or application retirement, with one sentence of justification from the chapter's table. Group the systems into three waves, beginning with a pilot wave of non-critical systems, and state what the team must have learned before the next wave starts. For the pilot wave describe the codification steps: import, review, drift detection, and the rollback available at each step.

Deliverable: A system inventory table with strategy per system, a three-wave plan with entry conditions, and the codification steps with rollback for the pilot wave.

Your work

Self-test

Choose an answer to see whether it is right, or open the answer below each question.

Which migration strategy does the chapter's table describe as suited to the majority of enterprise migrations?
Show the answer
D. Lift-and-improve (hybrid)
Lift-and-improve selectively re-architects critical components while keeping most unchanged, and the table lists it as best suited for phased modernisation, risk-balanced approaches and the majority of enterprise migrations.
Why does the chapter follow an import of existing resources with drift detection?
Show the answer
A. To prove the template describes reality before any further update
The import is a reviewed change set followed by drift detection, so that the template is proven to describe reality before any further update touches the resources.
What does the chapter recommend doing before critical systems are migrated?
Show the answer
B. Running pilot projects with non-critical systems
Pilot projects with non-critical systems enable team learning and process refinement before critical systems migration commences.