From monoliths to modular mastery: Choosing your composable commerce migration strategy

Composable commerce promises a more flexible, scalable and innovative future for retailers. But understanding the opportunities offered by composable commerce architectures is only part of the story. The real challenge lies in uncovering if a move to composable architecture could truly benefit a business and identifying the right strategies for a successful migration.

With tight budgets, demanding goals and limited resources, retail CTOs aren’t making significant platform decisions because they’d prefer a prettier architecture. They make the move to composable commerce because their existing system is hurting the business. That might be excessive lead times to launch a campaign, checkout processes buckling during peak demand periods or competitors beating them to new channels and innovative customer experiences. These are all signals that it might be time to migrate to composable architecture.

In this blog, we outline the journey to composable commerce and how to pick a migration path that delivers measurable business outcomes while protecting business continuity.

If you want more detail into the processes and specific tactics, you can read the full migration framework in our ebook “Composable commerce: The blueprint for modern e‑commerce.”

Start with a strategic assessment

Excited by the potential of composable commerce, organisations are often tempted to dive headfirst into implementation. But, before a single line of code is touched, it’s essential to understand the specific elements hurting revenue, development speed or customer experience.

A short discovery workshop can help uncover the domains where modular architecture can add real value, highlight the organisational processes and team topologies that will shape success and pinpoint the specific use cases to focus on. It also enables teams to define service-level baseline metrics so that measurable outcomes can be tracked, communicated and celebrated throughout the migration.

This is more than just a technical exercise. A business-led, domain-driven assessment lays the groundwork for migration and helps avoid the trap of building better architecture without gaining any business benefits. By understanding exactly where the legacy system falls short, gauging readiness for change, and defining what success looks like with measurable outcomes, businesses can build a strong foundation for transformation.

From assessment to execution: Choosing the right migration approach

There is no one-size-fits-all approach to migration. Each strategy involves trade-offs between speed, risk and complexity. But with a clear strategic assessment in hand, organisations can make an informed decision at this crucial juncture in the journey.

Big Bang: Rare, radical but sometimes right

The Big Bang approach involves the single-step wholesale replacement with the legacy platform switched off, and the new stack switched on, in one coordinated release. A common downside of Big Bang migrations is the drive for full feature parity with the legacy system, since there’s limited room to learn and adapt mid-process. This often results in unnecessary features being rebuilt, inflating cost and complexity — and those features rarely get retired later due to sunk cost fallacy.

Best suited for organisations with a brittle platform that would cost more to change than replace or where a business can weather a multi-month freeze while a new solution is built, a big bang offers rewards in agility, performance and scalability.

But with high reward comes high risk. Coordinating the simultaneous replacement of all system components demands meticulous planning, testing, and cross-team collaboration, with integration cut-over, data migration and culture shock all potential pitfalls. A single misstep can lead to widespread outages and disruption, as TSB bank found in 2018 when a failed Big Bang migration left customers unable to access online accounts for several weeks.

Strangler Fig: The safest default, requiring disciplined delivery

The Strangler Fig pattern offers an incremental, evolutionary approach that grows new capabilities around the edges of the legacy until the old is gradually “strangled” and phased out.

Organisations maintain operational continuity while carving out steel threads, such as product search, into self-contained components that are rigorously tested before going live. It enables high-value areas to be prioritised and benefits to be seen earlier in the process, with real-world feedback and performance also helping to shape future plans. Techniques like canary releases (more on that below) help reduce risk as new services are introduced

For a large Australian retailer, this approach helped transform its customer experience and operational efficiency. By replacing product availability and online order sourcing components with microservices, it could calculate real-time stock levels and optimise order fulfilment. During the 2022 Black Friday sales, it reduced manual order fulfilment reassignments between stores from several hundred to just one, a substantial reduction in time while increasing resource efficiency.

However, running the legacy and new systems in parallel can introduce additional complexities in integration, monitoring, reporting and maintenance, demanding a disciplined approach to governance and a robust infrastructure capable of handling hybrid environments.

Hybrid tactics: Blending the benefits of radical and incremental change

Organisations can also take a pick-and-mix approach, borrowing elements from the two extremes to fine‑tune the balance of speed, risk and investment for each context.

Tactics can include:

• Lift-and-shift then refactor – Moving the monolith to a new infrastructure (often cloud‑based) as a first step, followed by a gradual refactoring into microservices.
• Canary releases – Enabling composable components to operate alongside the legacy system, reducing risk by maintaining a fallback option throughout the migration.
  • This tactic is often chosen when teams want to reduce infrastructure costs or exit on-premise data centres quickly, while buying time to plan and execute a gradual decomposition of the monolith. It allows organisations to get early wins from cloud elasticity and managed services before tackling deeper architectural change.
  • Despite the term “lift-and-shift,” these migrations often involve non-trivial code updates — including adapting to cloud-native services, handling new deployment models, and sometimes reworking integrations. So while full refactoring is deferred, the ‘lift’ phase often still requires code and architectural adjustments — from adapting to cloud-native infrastructure to resolving deployment and integration challenges.

Mini-lith consolidation – Combining a small set of tightly coupled services into a single deployable unit can reduce latency, simplify interfaces and ease operational complexity. This pattern can help keep cognitive load manageable, especially when decomposed services prove too granular or interdependent in practice

It’s also important to remember that 100% extraction of the monolith is not always required, as previously explored in our Target Cloud Operating Model whitepaper and heritage services blog series. Many retailers benefit from using modular architectures for their highest-value areas, leaving a smaller, stable legacy core in a “lights-on” mode. This approach can help balance cost and risk in the short term, ensuring that investment is focused where modularity will deliver the most value. However, teams must still plan for eventual replacement, particularly to address maintainability and security concerns that can arise over time.This approach can help balance cost and risk, ensuring that investment is funnelled into domains where modularity will have the biggest impact on the business.

Measuring and maintaining progress

Long-running modernisation programmes can start strong but lose steam as day-to-day demands take over.  Decision drift, talent turnover, increasing pressure and benefit invisibility are all common signs of migration fatigue and stalling progress.

To keep momentum, make progress visible. Publishing a living scoreboard and celebrating micro-milestones that demonstrate the measurable value of the work can help combat fatigue. These can include a reduction in licensing costs, improvements in business agility or savings in operating costs. Combined with ring-fencing of capacity, timeboxing specific migration pieces and rotating the ownership of shrinking legacy components, organisations can also make space for teams to focus on the migration tasks at hand.

Migration is a marathon made of sprints, with the organisations that finish being the ones that continuously prioritise team morale and measure progress.

Align strategy with business ambition 

Composable commerce isn’t a destination. It’s an operating model – one that helps retailers become more adaptable, more innovative and better able to serve their customers. Choosing the right migration strategy – if a migration is required at all – is the most pivotal decision in any retailer’s move to composable commerce and the right choice will be one that aligns with business ambition to unlock value fast.

If you’re planning your migration or are struggling to unlock the real value of composable commerce, Equal Experts can help. Contact our team to start your journey with a focused two-week discovery sprint to clarify your pain points, where modular architecture can create real value and how to achieve your migration goals.

Don’t forget to download our latest eBook, “Composable commerce: The blueprint for modern e‑commerce” for our full migration framework and more insights.