Migration Guides
Practical, battle-tested paths for migrating legacy technology stacks without breaking production or burning out your team
Technology migrations are one of the biggest sources of technical debt. A botched migration doubles your maintenance burden instead of eliminating it. These guides give you proven strategies, realistic timelines, and the hard-won lessons that keep migrations on track.
Why Migrations Create So Much Debt
Most teams start a migration with good intentions and a clean plan. Then reality hits. The old system has undocumented behaviors. The new platform does not support a feature you assumed it would. A critical deadline forces you to ship half-migrated code. Suddenly you are maintaining two systems instead of one, and the "temporary" bridge code becomes permanent.
Industry data tells the story: 70% of large-scale migrations exceed their original timeline by 50% or more. The most common reason is not technical complexity - it is underestimating the scope of what needs to change and overestimating how much can run in parallel.
The guides below break down specific migration paths into phases you can execute incrementally. No big-bang rewrites. No "we will figure it out as we go." Just structured approaches that teams have actually used to ship successfully.
Migration Paths
Legacy .NET to Modern .NET
Migrate from .NET Framework 4.x to .NET 8+ without a risky rewrite. Covers Web Forms to Razor/Blazor, WCF to gRPC, Entity Framework 6 to EF Core, and the Strangler Fig approach for incremental adoption.
jQuery to Modern JavaScript
Remove jQuery dependencies one pattern at a time. Covers DOM manipulation, AJAX to fetch, event delegation, animation replacements, plugin alternatives, and how to run jQuery and vanilla JS side by side during the transition.
Universal Migration Principles
These principles apply to every technology migration, regardless of the stack. Ignore them at your own risk.
Migrate Incrementally
Ship value at every phase. If the migration gets paused or cancelled, whatever you have completed should still be usable. Never bet everything on a single cutover date.
Test Both Systems
Run the old and new systems in parallel. Verify that outputs match before cutting over. Automated comparison tests catch discrepancies that manual testing misses.
Always Have a Rollback Plan
Every migration step should be reversible. If you cannot explain how to undo a change in under five minutes, the change is too large. Feature flags, database versioning, and blue-green deployments are your safety net.
Audit Before You Build
Document every behavior of the old system before writing a line of new code. Undocumented business rules, edge cases, and implicit dependencies are where migrations fail. Inventory first, migrate second.
Align the Whole Team
Migrations fail when only part of the team buys in. QA, ops, product, and support all need to know the plan, the timeline, and what changes for them. Surprises kill migrations.
Measure Progress, Not Effort
Track the percentage of traffic or features running on the new system, not hours spent. "We completed 200 story points" means nothing if production still runs on the old stack.
Migration Anti-Patterns
These are the patterns that sink migrations. If you recognize any of these in your current plan, stop and course-correct before you go further.
The Big Bang Rewrite
"We will rewrite everything from scratch and flip the switch on launch day." This almost never works. The old system keeps evolving while the new one is being built, requirements drift, and the cutover becomes a terrifying all-or-nothing gamble. Joel Spolsky called this the single worst strategic mistake a software company can make. Use the Strangler Fig pattern instead.
No Rollback Plan
"If something goes wrong, we will figure it out." This is not a plan - it is a prayer. Every migration step needs a tested, documented rollback procedure. If you cannot roll back a deployment in under 15 minutes, your migration steps are too large. Practice rollbacks in staging before you need them in production.
Skipping Tests
"We will add tests after the migration." No, you will not. Migrations without comprehensive tests are just moving bugs from one system to another. Write characterization tests for the old system first, then use those same tests to validate the new system produces identical results. The test suite is your proof that the migration worked.
Migrating Everything at Once
"While we are at it, let us also upgrade the database, redesign the UI, and restructure the team." Scope creep is the silent killer of migrations. Each migration should change exactly one major thing. If you need to modernize the database and the framework and the frontend, those are three separate migration projects with their own timelines and rollback plans.
Timeline Planning Reality Check
Every migration estimate is wrong. The question is how wrong. Use these guidelines to build timelines that account for reality.
Typical Timeline Multipliers
- 1.5x Well-documented system, strong test coverage, experienced team
- 2-3x Moderate documentation, some tests, team has done a migration before
- 3-5x Poor documentation, few tests, first migration for the team
- 5x+ No documentation, no tests, no one who built the original system is still on the team
Phase Planning Checklist
- Discovery and audit (2-4 weeks minimum)
- Proof of concept with the riskiest component first
- Pilot migration of one non-critical module
- Phased rollout with checkpoints and go/no-go gates
- Decommission old system only after full validation
- Post-migration retrospective and documentation update
Pro tip: Build "migration buffer" into every sprint. Expect that 20-30% of your migration effort will go toward unexpected discoveries - undocumented APIs, hidden dependencies, data format inconsistencies. If you do not use the buffer, ship the next phase early. But you will use it.
Related Resources
Migrations do not happen in a vacuum. These resources cover the strategies and patterns that support successful migrations.
Frequently Asked Questions
Migrate when the platform itself is the bottleneck - when the framework is end-of-life, when security patches are no longer available, or when hiring developers who know the old stack is becoming impossible. If you can still deliver features and maintain security on the current platform, refactoring is usually the better investment. Migration is expensive and risky; do not do it for aesthetics or resume-driven development.
No. A feature freeze signals to the business that engineering is a cost center, not a value driver. The whole point of incremental migration is that you can keep shipping features on the old system while migrating piece by piece. New features in already-migrated areas should use the new stack. New features in not-yet-migrated areas use the old stack. This is messy but realistic - and it keeps your stakeholders on your side.
Separately. Data migration has its own risks and timeline. Start by supporting dual reads - the new code reads from both old and new data stores. Migrate data in batches with validation checks, not in one shot. Keep the old data store read-only as a fallback until you have verified every record. Schema differences, encoding issues, and orphaned records will surprise you, so budget time for data cleanup.
Most successful migrations allocate 20-30% of sprint capacity. This is enough to make steady progress without starving feature development. During critical cutover phases, you might temporarily bump to 40-50%, but communicate this to stakeholders well in advance. The worst approach is 100% migration for months followed by a panicked return to features - that pattern destroys team morale and stakeholder trust.
Frame it in business terms: security risk (end-of-life means no patches), hiring costs (fewer developers know the old stack), velocity impact (features take 3x longer in the legacy system), and opportunity cost (competitors ship faster). Quantify everything. "We lose 40 developer-hours per sprint to workarounds in the legacy payment module" is more convincing than "the code is old." See our selling to management guide for detailed frameworks.
If you migrated incrementally, you are in a recoverable position. The pieces you already migrated are working on the new stack. The pieces you have not migrated are still working on the old stack. You can pause, reassess, and decide whether to continue, change approach, or accept a hybrid state. This is exactly why incremental migration beats big-bang rewrites - a "failed" incremental migration still leaves you in a better position than when you started.
Ready to Plan Your Migration?
Start with the guide that matches your stack, or download our migration playbook template for a structured planning framework.