Robin Dickie, head of technology and delivery at Viare and eStar, discusses how to upgrade systems without disrupting the business.
Retail technology projects frequently stall, overrun budgets, or fail to deliver – not because the new technology is "wrong," but because implementation is often wired for a "Big Bang." So, how do we modernise without the meltdown? The answer lies in a methodology that allows for a gradual, controlled transition: the Strangler Fig.
What is the Strangler Fig Pattern?
In nature, a Strangler Fig begins in the upper branches of a host tree. It slowly sends roots to the ground, gradually enveloping the original tree until the fig becomes the new, stable structure and the host is no longer needed.
In practical terms, we treat the legacy system as a host: stable and functional, but rigid. By building a modern, agile layer that wraps around this core, we begin to divert the "nutrients" the data and customer traffic to newer, more flexible services. Much like the fig, the new system doesn't replace the host immediately; it supports the business while gradually assuming its vital functions, eventually becoming the new primary structure.
Amazon’s "Obidos" Evolution
In the early 2000s, Amazon was struggling under a monolithic application known as "Obidos." As they grew, this single, massive codebase became a bottleneck.
Instead of pausing the business for a multi-year rebuild, Amazon’s leadership committed to a Strangler Fig approach. They began decoupling specific business functions starting with simple services like "customer reviews" and "recommendations" and moving them into independent microservices.
By the time the transition was complete, Amazon had evolved into a web of thousands of independent services. They didn't stop the business to rebuild; they rebuilt while the business grew. This shift is what allowed them to scale from a book retailer into a global infrastructure giant. It proved that the competitive edge isn't just the code you write, but the discipline with which you deliver it.
From Roots to Results: The 4 Stages of the Shift
This shift moves from a high-risk "Big Bang" mindset to one of continuous value delivery. By deconstructing the transition, you provide immediate operational benefits in manageable stages while protecting the stability of the existing core.
1. Identify the Highest Value Target Implementation discipline starts with resisting the urge to fix everything at once. Identify one high-friction business capability that is independent enough to be isolated – for example, Inventory Lookup or Loyalty Calculation. By focusing on a single vertical, you reduce the surface area for failure and deliver a tangible win to the business in months, rather than years.
2. Establish the Interception Layer The transition requires an API Gateway or "Proxy" positioned between your front-end (e.g., eCommerce site or POS) and your legacy back-end. Initially, this gateway simply passes requests through to the old system. However, it provides the "hook" needed to reroute traffic. Once in place, you can point specific requests to your new microservice without the front-end or the customer ever knowing a change has occurred.
3. Build and "Shadow" the New Service Before going live, run your new service in Shadow Mode. Every time a request is made, the Interception Layer sends it to both the legacy system and the new service simultaneously. You compare the results in the background, only switching over once the new logic matches the legacy output perfectly across thousands of real-world transactions. This ensures the new engine is battle-hardened before it ever carries a live load.
4. Managed Cutover and Legacy Decommission The final stage is a controlled "Canary" migration. You route a small fraction of traffic—perhaps 5%—to the new service while monitoring performance in real-time. As confidence grows, you incrementally dial up the traffic to 100%. Once the new service is stable, the legacy code path is physically removed to prevent "technical debt," and the cycle repeats for the next business vertical.
The competitive edge in delivery belongs to those who treat modernisation as a persistent, low-risk capability. By following this gated, incremental process, you ensure technology supports growth instead of acting as an anchor. You don't need to replace the whole plane to upgrade the engines; you just need the discipline to change one part at a time.
This is a partnered content series with Viare and eStar.