The Art of Re-Architecture - Droidcon India 2025

Every engineer eventually inherits a legacy codebase — a complex beast that slows down innovation and frustrates teams. But how do you start taming it? What truly constitutes "legacy," and where do you strike first for maximum impact?

This talk shares hard-learnt lessons from the front lines of building and re-architecting some of the world's most complex food delivery apps at Foodpanda, Foodora, and Delivery Hero. We will move beyond theory to offer a practical playbook for transforming large-scale Android applications while navigating the intricate dance of technical vision and business demands.

This session will cover five key lessons:

Defining Legacy: A framework for identifying legacy code, locating architectural hotspots, and strategically choosing your first refactoring target.

The Conundrum of Refactor vs. Rearchitect: Understanding the critical difference, when each approach is relevant, and what they truly entail for your team and timeline.

The Marriage of Product & Engineering: Mastering the balancing act of delivering new features while simultaneously executing a large-scale re-architecture without losing momentum.

Convincing Stakeholders: How to effectively communicate a compelling technical vision, get buy-in from product and business leaders, and become a trusted team player.

Choosing Your Weapons: A pragmatic guide to selecting the right architectural patterns, tools, and modularization strategies for the job at hand.

Join this session and tackle your most daunting legacy challenges in your code-bases, leaving with a playbook that has been tested and proven at scale.

Transcript

1. The Art of Re-architecture Lessons from the trenches at Foodpanda and Delivery Hero Sid Patil Rutvik Bhatt
2. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt About the speakers 👋 Sid Patil • I work at Delivery hero, based in Berlin 🇩🇪 • Building products for 10+ years • Previously built chat-based UPI payments at Paytm • Into AOSP, co ff ee and photography • Read more at siddroid.com
3. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt About the speakers 👋 Rutvik Bhatt • Engineering lead at Delivery Hero 🇩🇪 • I support 20 engineers across 2 teams • Prev. Experience in Ad-Tech at Taboola 🇹🇭 • Traveler, Road-trip junkie, plays badminton and table tennis • Read my thoughts on rutvikbhatt.com
4. 70 countries and 11 Brands
5. “Re” Architecture
6. Five lessons, one story
7. Home & Vendor Tiles
8. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt
9. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt Vendor Tile
10. You cannot change your starting coordinates. You can only change your trajectory. Lesson 1
11. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt The Myth of the Blank Canvas • There is no starting line. • Start with the messy reality. Don't dream of a blank canvas • Legacy is just a previous success. • Understand before you delete. • Apply the Chesterton’s Fence Principle • Learn the constraint, or you will repeat it.
12. Identifying Legacy
13. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt What is Legacy ❌ Old code, someone else's code, code without tests ✅ Code that prevents you from moving fast Data gets budget. "It feels bad" doesn’t.
14. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt Identifying Legacy It’s not about age. It’s about velocity. The Signal The Symptom Estimate In fl ation A simple 2-day task mysteriously becomes a 2-week struggle. The Hack Ratio You say "Let's just patch this for now" more often than "Let's build this right." API Friction Modern tools (eg Compose, Coroutines) actively fi ght against your architecture. The stark “No” Engineering often has to say “No” to product teams due to technical complexity.
15. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt Our “Legacy” Before we re-architected the Home & Vendor Tiles • The SDUI was tightly coupled with custom SDKs • Integrating new services was not easy • High product development estimates • Older backend stack • Tiles could not be customized dynamically
16. Re-architect? Refactor? Re-write?
17. Lesson 2 Re-architect for the future, Refactor for the now
18. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt The Distinction Refactoring is tactical. Re-architecture is strategic. Refactoring Re-architecting Frequency: Daily / Continuous Frequency: Rare / Phased Scope: Class & Function level Scope: Module & System level Goal: Clean code, Readability Goal: New Capabilities, Scalability Example: Renaming, Decoupling, Testing Example: Static architecture to SDUI
19. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt When to Re-architect? • Fighting architecture daily • Features take 3x longer than they should • Tech debt growing exponentially • The current solution is playing catch-up with Product bets • Rapid experimentation is often di ff i cult
20. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt Re-architecting Vendor Tile Dynamically server driven component via Backend • New backend stack with federated GraphQL • Component level UI customisation • Easy of integration with new services • Improved time-to-deploy • Each component of the tile is customisable
21. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt From our team Home redesign and GraphQL driven vendor tiles • Redesigning the Home-screen: foodpanda, foodora and Yemeksepeti by Aswin Ranganathan • Delivering Faster Cross-Platform UX Iteration at Delivery Hero with Server- Driven Tiles by Arne Wieding & Oluwapelumi Olaoye
22. Marriage of product & engineering
23. Lesson 3 Move the product, not just the tech.
24. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt Making the Marriage Success Product and Engineering • Look at the Product Roadmap fi rst. • The Rule: "Re-architecture is supplicant to product objectives." • Move in parallel tracks. Architecture team enables feature teams. • Adopt the strangler fi g pattern, build new architecture, ship gradually. • Your re-architecture MUST translate to business values.
25. Convincing Stakeholders
26. Lesson 4 Trust enables technical work
27. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt The Hard Sell • Build Trust First • Speak Their Language • Show the Numbers, Show ROI • Frame as Risk Management - Product, Business and Engineering have di ff erent risks, learn all three languages • The Pilot Project Strategy - Start Small, Prove Value
28. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt Pitching the long game We can limp along, or invest now for sustained velocity
29. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt The Diagnosis The Diagnosis Rigid Structure: Can’t Reorder Homescreen Components Slow Time To Market: Changing Vendor Tiles Takes 2 weeks Over fetching Chaos: Scattered Business Logic, fetching 10x needed Data Duplicate Everything: Same feature, 3 implementations Product Evolution Blocked: Architecture can’t support new discovery journeys
30. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt Big Bets: Con fi gurable Vendor Tile & Home Re-arch
31. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt The Journey • Before Pitching, Deep Product Alignment • The Pilot - Start impossibly small. Prove Value! • Prove it at Scale - Con fi gurable Vendor Tiles • The Trust was built. • The Big Move - GraphQL Federation
32. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt
33. Monitoring success
34. Lesson 5 Progress, not perfection.
35. The ship of Theseus
36. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt Chase Progress Never go dark for 6 months. • Progress is success. • Replace the ship plank by plank while it's sailing. • Perfection will never be attained. • Ship incrementally. • A perfect architecture that isn't shipped is worth less THAN a messy one that serves millions of users.
37. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt Visibility & Evangelism • Create visibility: • Build dashboards. "40% of modules migrated." Gamify it. • Build adoption trackers that stakeholders can see. • Do peer-to-peer reviews, understand if junior devs like it • Monitor stability metrics closely: screen performance, business metrics, fi rebase dashboards and alerting
38. The Art of Re-Architecture, Droidcon India 2025 Sid Patil & Rutvik Bhatt The Toolkit Art for the craft Category The Technique The Tool Impact Isolation Safety walls Wrapper Classes / Facades Prevents "legacy rot" from leaking into your clean new modules. You build a wall; the old system talks to the wall, not your new code. Migration Strangler Fig Pattern Routing Rules Allows you to intercept calls to speci fi c features and route them to the new system one by one, gradually "strangling" the old codebase. Safety Branch by Abstraction Feature Flags Lets you merge un fi nished architectural changes into the main branch safely. You can toggle the new architecture on for 1% of users to test stability. Enforcement Fitness Functions Lint Checks (Crucial) Automates your rules. If a developer tries to make the "UI Layer" talk directly to the "Database" (bypassing logic), the build fails automatically. Discovery Hotspot Analysis Code Churn vs. Complexity Graphs Shows you where the "scariest" code lives. Don't rewrite stable code; rewrite the code that changes often and breaks often.
39. Takeaways
40. Our Lessons You can only change your trajectory. Re-architect for the future, Refactor for the now. Move the product, not just the tech. Trust enables technical work. Progress, not perfection.
41. Thank You, Droidcon India! Sid Patil Rutvik Bhatt