Original post

From LinkedIn: https://www.linkedin.com/posts/matthias-patzak_cto-technology-activity-7312449287647375360-ogNg?utm_source=share&utm_medium=member_desktop&rcm=ACoAAAAWqBcBNS5uEX9jPi1JPdGxlnWwMBjXwaw

Summary of the question

As CTO for a mainframe rebuild (core banking/insurance/retail app, 100 teams/1000 people with Cobol expertise), considering Java/Kotlin, TypeScript/Node.js, Go, and Python. Key decision criteria are technical maturity/stability, robust community, and innovation/adoption. The CTO finds these criteria sound and seeks a language recommendation.

TL;DR: my response

• Team, mainframe rebuild: Java/Kotlin are frontrunners due to maturity, ecosystem, and team’s Java-adjacent skills. Go has niche potential. TypeScript/Node.js and Python less ideal for core.
• Focus now: deep PoC comparing Java (Spring Boot) vs. Kotlin on our use cases. Evaluate developer productivity, readability, interoperability, performance.
• Develop comprehensive Java/Kotlin training for our 100 Cobol-experienced teams.
• Strategic adoption plan (Java, Kotlin, or hybrid) based on PoC and team input is next.
• This balances proven stability with modern practices on the JVM for our core.

My detailed opinion

As a CTO with experience in these large-scale transformations, my priority remains a solution that balances technical strength with the pragmatic realities of our team’s current expertise and long-term maintainability.

While Go offers compelling performance characteristics, the specific demands of our core business application – be it in banking, insurance, or retail – often prioritize a mature ecosystem, robust enterprise patterns, and a more gradual transition path for our significant team. Given our 100 teams deeply skilled in Cobol, the learning curve and the availability of readily transferable concepts become key considerations.

Therefore, while acknowledging Go’s strengths in certain cloud-native scenarios, I want to emphasize the strategic advantages of the Java/Kotlin ecosystem for our primary language choice, with a deliberate hesitation and deeper exploration between these two JVM-based options.

Re-emphasizing Java and Exploring Kotlin More Deeply:

• Java’s Enduring Strength: Java’s decades of proven stability in building mission-critical enterprise systems cannot be overstated. The JVM’s resilience, the vast array of mature libraries and frameworks (especially Spring Boot), and the well-established architectural patterns provide a solid and predictable foundation. Moreover, the sheer size of the Java developer community ensures a deep pool of talent and readily available support for our teams as they transition. For a core system in a regulated industry, this level of established maturity significantly mitigates risk.

• Kotlin’s Modern Edge and Interoperability: Kotlin presents a compelling evolution on the JVM. Its modern syntax, null safety features, and concise code can lead to increased developer productivity and reduced boilerplate – benefits I’ve witnessed firsthand in JVM-based projects. Crucially, Kotlin’s seamless interoperability with Java is a major strategic advantage. It allows us to:

  • Gradually adopt Kotlin: Teams can start by integrating Kotlin into existing Java codebases, allowing for a phased learning process without a complete overhaul.
  • Leverage the entire Java ecosystem: Kotlin developers can effortlessly use any Java library or framework, giving us access to the vast resources of the Java world.
  • Attract modern talent: Kotlin’s growing popularity can help us attract developers who are excited about working with a modern, yet stable, language on a proven platform.

Why Hesitate Between Java and Kotlin?

The decision of whether to primarily adopt Java or Kotlin (or a strategic mix) requires careful consideration of our team’s specific needs and the long-term vision:

• Learning Curve: While Kotlin is designed to be approachable for Java developers, there is still a learning curve associated with its new syntax and features. We need to assess how quickly our large Cobol-experienced team can become proficient in Kotlin.
• Team Preference and Buy-in: Understanding our developers’ preferences and ensuring buy-in for the chosen language is crucial for successful adoption.
• Long-Term Ecosystem Evolution: While both Java and Kotlin have strong futures on the JVM, we need to consider the long-term trends and the level of investment in each language within the enterprise space.
• Specific Use Cases: Certain parts of our system might benefit more from Kotlin’s conciseness or specific features, while other more established components might initially remain in Java.

Proposed Next Steps (Revised Focus):

1. Targeted Proof of Concept (PoC) – Deep Dive into Java and Kotlin: Instead of a broad PoC including Go, let’s focus our initial efforts on a detailed comparison of Java (using Spring Boot) and Kotlin on representative use cases from our core business application. This PoC should specifically evaluate:
   • Developer Productivity: How quickly can teams with a Java-adjacent mindset (after initial training) develop and maintain code in both languages?
   • Code Readability and Maintainability: How do the resulting codebases compare in terms of clarity and ease of understanding for a large team?
   • Interoperability Scenarios: How seamlessly can Java and Kotlin code coexist and interact within the same project?
   • Performance Benchmarking: While the JVM provides a solid base, are there noticeable performance differences for our specific workloads?
2. Comprehensive Training and Upskilling Program: We need to develop a detailed training program that caters to our team’s Cobol background and provides clear pathways for learning both Java and Kotlin. This program should include hands-on exercises and mentorship opportunities.
3. Strategic Adoption Plan: Based on the PoC results and team feedback, we’ll develop a strategic adoption plan that outlines whether we’ll primarily focus on Java, Kotlin, or a hybrid approach. This plan should consider the long-term maintainability and talent acquisition goals.

While Go remains a valuable technology for specific niches, for the core of our mainframe rebuild, our focus should now be on leveraging the mature and evolving Java/Kotlin ecosystem and strategically determining the optimal path for our large and experienced team. This approach minimizes risk while embracing modern development practices on a proven platform.