title: Spring boot application gives 503 Service unavailable in the first minute
body: <p>After my application starts up I see this message in the log:</p>
  
  <pre><code>Started Application in 22.609 seconds (JVM running for 24.342)
  </code></pre>
  
  <p>but when I access the application in the browser I get a 503 error for a certain period of time. Not always the same, so not likely a timeout.</p>
  
  <p>Is this normal? What is taking so long? How can I debug this?</p>
  
  <p>Great idea to access port 8080 directly. Here I get a different behavior: The browser waits and after some time I see this:
  2017-11-10 09:40:37,276 [http-nio-8080-exec-1] WARN  o.a.c.util.SessionIdGeneratorBase - Creation of SecureRandom instance for session ID generation using [SHA1PRNG] took [88,709] milliseconds.
  I'll try -Djava.security.egd=file:/dev/./urandom now</p>