When asked to design an API gateway, I began by discussing the fundamental responsibilities such as request routing, authentication, and rate limiting. I emphasized the importance of load balancing and how different protocols could be supported. The interviewer seemed engaged but challenged my approach on handling security issues, prompting me to elaborate more on token validation and data encryption, which I felt was a bit of a red flag in my response.

As I progressed, I introduced the concept of microservices and how they communicate with the gateway. I mentioned using tools like NGINX for routing and Kong for API management. The interviewer asked follow-up questions regarding scaling, especially about handling large volumes of concurrent requests. I provided some examples but could have been clearer on the use of caching strategies and connection pooling.

The conversation shifted towards error handling strategies, and I mentioned implementing circuit breakers and fallback mechanisms. However, I overlooked discussing how to log and monitor API usage effectively, which the interviewer seemed to appreciate but pointed out was crucial for maintaining performance. This is an area I need to improve on; being more comprehensive in my approach could strengthen my design.

Towards the end, I had the opportunity to discuss deployment strategies like using Docker containers and Kubernetes for orchestration. The interviewer seemed satisfied with this part, as I tied back the scalable deployment to the initial design principles we had established. I felt a sense of relief as I was finally directing the flow of the conversation effectively, helping to showcase my experience.

Despite some areas where I faltered, I sensed that overall, the discussion was productive, particularly in touching on real-world implications of API design. The interviewer expressed interest in my potential fit for Shopify's fast-paced environment, which I took as a positive sign, yet there were still some topics that left me unsettled. Ultimately, I left the interview with a feeling of mixed emotions, knowing I had potential to show more clarity on certain points but also feeling engaged in the process.