I'm coming from the PHP/Python/JS environment where it's a standard to run multiple instances of web application as separate processes and asynchronous tasks like queue processing as separate scripts.
eg. in the k8s environment, there would be
- N instances of web server only, each running in separate pod
- For each queue, dynamic number of consumers, each in separate pod
- Cron scheduling using k8s crontab functionality, leaving the scheduling process to k8s
Such approach matches well the cloud nature where the workload can be scheduled across both smaller number of powerful machines and lot of less powerful machines and allows very fine control of auto scaling (based on the number of messages in specific queue for example).
Also, there is a clear separation between the developer and DevOps responsibility.
Recently, I tried to replicate the same setup with Java Spring Boot application and failed miserably.
Even though Java frameworks say that they are "cloud native", it seems like all the documentation is still built around monolith application, which handles all consumers and cron scheduling in separate threads.
Clear answer to this problem is microservices but that's way out of scope.
What I need is to deploy separate parts of application (like 1 queue listener only) per pod in the cloud yet keep the monolith code architecture.
So, the question is:
How do I design my Spring Boot application so that:
- I can run the webserver separately without queue listeners and scheduled jobs
- I can run one queue listener per pod in the k8s
- I can use k8s cron scheduling instead of App level Spring scheduler?
I found several ways to achieve something like this but I expect there must be some "more or less standard way".
Alternative solutions that came to my mind:
- Having separate module with separate Application definition so that each "command" is built separately
- Using Spring Profiles to instantiate specific services only according to some environment variables
- Implement custom command line runner which would parse command name/queue name and dynamically create appropriate services (this seems to be the most similar approach to the way how it's done in "scripting languages")
What I mainly want to achieve with such setup is:
- To be able to run the application on lot of weak HW instead of having 1 machine with 32 cpu cores
- Easier scaling per workload
- Removing one layer from already complex monitoring infrastructure (k8s already allows very fine resource monitoring, application level task scheduling and parallelism makes this way more difficult)
Do I miss something or is it just that it's not standard to write Java server apps this way? Thank you!
micronauttag as the question doesn't appear to involve Micronaut. – Jeff Scott Brown