Experience case study • Platform migration

Migrating a legacy framework containing thousands of tests to a distributed CI/CD platform

I led a six-month migration while product development and release validation continued on the legacy framework.

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This page answers:How do you replace a live validation framework containing thousands of tests while development continues?

Problem

One optical-networking product depended on a legacy automation framework containing thousands of tests, but execution, logs, history, and workflows were not centralized.

Challenge

Release validation and product development could not stop during the six-month migration. The legacy and replacement frameworks therefore evolved in parallel, making synchronization and behavioral equivalence more important than migrated-test counts.

My Contribution

I led a two-person migration effort.

  • I migrated the entire shared-library layer.
  • I owned integration with the distributed platform and CI/CD workflows.
  • The other engineer focused primarily on migrating individual test scripts.
  • Together, we migrated thousands of test cases across the sanity, smoke, and regression suites.
  • I built a dashboard to track progress, ownership, and synchronization.
  • I ensured ongoing legacy changes were reflected in migrated components.
  • I delivered code walkthroughs and training to support the team’s transition.

Migration architecture

From parallel operation to controlled cutoverThe legacy path stayed live while synchronization, staged migration, and equivalence checks prepared the replacement.
  • Legacy pathDevelopment and release validation continue
  • Migration controlOwnership, dependencies, and changes stay synchronized
  • New platformDistributed execution and CI/CD become the destination

Controlled replacement path

Progress is necessary; equivalent behaviour is the cutover gate.

  1. OperateKeep liveLegacy validation continues
  2. ControlSynchronizeTrack changes and ownership
  3. MigrateMove foundationsLibraries before scripts
  4. VerifyCompareScenarios, results, and time
  5. CutoverReplaceRetire the legacy path

Cutover guardrailLegacy-framework engineers verify required scenarios before retirement; confidential implementation details remain excluded.

Engineering Decisions

Migrate while development continued

Freezing the legacy framework would have simplified synchronization, but it would also have interrupted ongoing product work and release validation. I chose parallel operation and treated every relevant legacy change as migration work until cutover. This increased coordination cost, but protected delivery continuity.

Solve migration visibility early

I created a centralized dashboard for progress, ownership, and synchronization before the project became too large to coordinate informally. A shared view made drift and responsibility visible without depending on repeated status reconstruction. Maintaining the dashboard added process overhead, but reduced ambiguity across the six-month effort.

Migrate shared libraries before individual tests

I prioritized the common library layer because every migrated test depended on those foundations. This reduced duplicated adaptation work and gave the second engineer a more stable base for moving individual scripts. The trade-off was slower visible test-count progress at the beginning in exchange for less downstream rework.

Use equivalence—not volume—as the cutover gate

Thousands of migrated tests did not by themselves prove that the replacement was ready. We compared scenarios, results, coverage, and execution time, with legacy-framework engineers verifying the preserved behavior. This made retirement more deliberate, but prevented progress metrics from being mistaken for operational readiness.

Outcome

Before

Legacy execution on remote servers, fragmented logs and history, and engineer-managed infrastructure.

After

The legacy framework was retired; distributed execution, logs, history, and CI/CD workflows became centralized without interrupting release validation.

Evidence

Parallel execution comparisonEquivalent scenarios ran through both frameworks and results were compared for behavioral differences.
Suite-level timingSanity and full-regression execution times were compared before retirement.
Legacy-expert verificationEngineers who knew the original framework verified that required scenarios were preserved.
Migration architectureThe sanitized diagram above records sequencing, synchronization, and the cutover boundary.

What other engineers can reuse

Treat synchronization as migration work

When old and new systems evolve together, every relevant legacy change needs an explicit reconciliation path.

Migrate shared dependencies first

Moving common libraries before individual tests reduces duplicated effort and downstream rework.

Measure equivalence, not progress

A migrated test count does not prove readiness. Compare scenarios, results, coverage, and execution time.

Include legacy experts

Engineers who understand the original system can identify behavioural gaps that automated comparisons may miss.

Plan knowledge transfer

A replacement is not operationally complete until its future maintainers can understand and support it.

Key takeaway

A migration is complete only when the new system reproduces the required behaviour, the two implementations have stopped drifting, and the receiving team can operate the replacement independently.

Public evidence boundary: This case study excludes confidential architecture, product details, internal measurements, staffing information, and customer information.

What This Project Demonstrates

Platform Engineering Leadership

Led the integration and shared-library work that moved thousands of tests onto a distributed execution platform.

Change Management

Kept two evolving frameworks synchronized while development and release validation continued.

Evidence-Based Cutover

Used scenario, result, coverage, and execution-time comparisons—not migration counts—as the retirement gate.

Operational Continuity

Sequenced the migration so release validation continued throughout the six-month replacement effort.

Knowledge Transfer

Included legacy experts in verification and prepared the receiving team to operate the replacement independently.

This project demonstrates my ability to lead a live platform migration while balancing technical execution, operational continuity, and organizational adoption.

Reflection

I would make the same core decisions: keep delivery running, migrate shared foundations first, and require behavioral equivalence before retirement. With today’s knowledge, I would automate more of the synchronization and comparison evidence where confidentiality and platform constraints allow, so the dashboard records fewer manually reconciled signals.

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