HADOOP-9181 went in, the secondary namenode immediately shuts down after it is started. From the startup logs:
I looked into the issue, and it's shutting down because SecondaryNameNode.main starts a bunch of daemon threads then returns. With nothing but daemon threads remaining, the JVM sees no reason to keep going and proceeds to shutdown. Apparently we were implicitly relying on the fact that the HttpServer QueuedThreadPool threads were not daemon threads to keep the secondary namenode process up.