We're always eager to learn about the impactful work that candidates have done in their careers. Could you describe the experience you are most proud of, elaborating on your role, the challenges you faced, and the positive impact your work had?

Proudest Accomplishment

As a senior software engineer with 8 years of experience, primarily at Google and now at a smaller startup in San Francisco, I've contributed to numerous projects. However, the accomplishment I'm most proud of is leading the migration of a critical, high-traffic service from a legacy monolithic architecture to a microservices-based architecture.

Background

At Google, I was part of a team responsible for a core service that handled user authentication and authorization. This service was monolithic, difficult to scale, and a bottleneck for many other teams. It was also using older technologies which made maintenance increasingly challenging.

The Challenge

The existing system was fragile, any changes had the potential for cascading failures. We had several critical requirements:

• Zero Downtime Migration: The migration needed to be seamless to users. Any downtime would have significant impact.
• Performance: The new architecture needed to maintain or improve the existing performance levels. Authentication is latency-sensitive, and any increase could noticeably degrade the user experience.
• Scalability: The new architecture needed to scale horizontally to handle increasing user traffic and future growth.
• Maintainability: The new architecture needed to be easier to maintain, test, and deploy.

The Approach (STAR Method)

Situation: We faced the challenge of migrating a critical, monolithic authentication service to a microservices architecture to improve scalability, maintainability, and performance while ensuring zero downtime.

Task: My role as the tech lead was to design and implement the migration strategy, coordinate with multiple teams, and ensure that the new system met all requirements.

Action:

1. Defined a Phased Migration Strategy: We couldn't do a big-bang rewrite. Instead, we opted for a phased approach, gradually migrating functionality to microservices.
2. Developed a Compatibility Layer: To facilitate the migration, we created a compatibility layer that allowed the new microservices to interact seamlessly with the old monolithic system.
3. Implemented Feature Flags: Feature flags were used extensively to control the rollout of new microservices and to quickly rollback if any issues arose.
4. Rigorous Testing: We implemented extensive unit, integration, and end-to-end tests. We also conducted load testing to ensure the new architecture could handle the expected traffic.
5. Monitoring and Alerting: We set up comprehensive monitoring and alerting systems to detect any issues during and after the migration.
6. Collaboration: This was by far the biggest hurdle. Since the system was used across all of Google, communicating the changes and ensuring buy-in from other teams was an absolute necessity.

Result:

The migration was successfully completed with zero downtime. The new microservices architecture significantly improved scalability and maintainability. We saw a 20% reduction in average response time for authentication requests. The team also reported a noticeable decrease in development and deployment time due to the modular nature of the new system.

What I Learned

This project taught me the importance of careful planning, communication, and collaboration when undertaking a large-scale migration. It also reinforced the value of testing and monitoring in ensuring a successful outcome. Furthermore, it highlighted the benefits of microservices in terms of scalability and maintainability.

I'm proud of this accomplishment because it was a complex and challenging project with high stakes, and I was able to lead the team to a successful outcome through careful planning, execution, and collaboration. The skills I developed during this project have been invaluable in my subsequent roles.