Optimizing Spring Boot Warm-up Logic with Custom Annotations and Reflection

Spring Boot applications can experience latency due to a Cold Start on the first request to external resources (DB, Redis, etc.) right after startup. This causes degraded user experience and timeouts.

The existing WarmUpRunner approach required manually calling each service, resulting in a lot of code duplication, and it operated synchronously, which had the limitation of lengthening the application startup time.

To improve this, the @WarmUp annotation and AppStartupWarmupRunner were introduced. This approach has the following characteristics.

• Automation and extensibility: Since methods annotated with @WarmUp are automatically discovered and executed via reflection, no separate modification is needed when adding a new service.
• Asynchronous parallel processing: By leveraging Kotlin Coroutine, multiple warm-up tasks are performed asynchronously and concurrently, reducing initialization time.
• Flexible configuration: By specifying WarmUpType and parameters in the annotation, warm-up can be performed to fit various scenarios and conditions.