title: Connection pooling with HikariCP, springboot and kubernetes
body: <p>I am using hikariCP for connection pooling in my reactive spring boot application running in kubernetes cluster. There will be lots of blocking calls and multiple database queries, so ideally more no of database connections would help, provided the availability of cpu cores.
  Providing all the cpu core to one kubernetes container will waste resource as the spike in requests will not always be there. So I am trying to explore how to utilize the autoscaler in kubernetes so that new application containers can be spinned up with increase in the no of requests. Two concerns:</p>
  
  <ul>
  <li>I tried the hikari configuration <strong>com.zaxxer.hikari.blockUntilFilled=true</strong> to keep the no of connections filled up during the application startup. But when using autoscaler with increasing no of requests, this will cause delays in the response as connection creation in the pool would take time. Is it better to use hikari's dynamic connection creation based on spike in demand rather than creating all the connections at once (during the startup).</li>
  <li>Also, each kubernetes container will be    a new instance of application, how do we manage the no of database connections created.</li>
  </ul>
  
  <p>I did a sample load test with jmeter and could see improved performance (and no timeouts etc) with large no of requests when using a fixed no of active database connections. There were large no of thread interrupted exceptions when there was no fixed connection pool size provided and connections were getting created dynamically with increased no of requests.</p>
  
  <p>Any insights will help.</p>