I have two questions for which I couldn't find any popular/widely accepted solutions:
What is the easiest way to start zookeeper server using Java Program?
And, is it possible to add servers to zookeeper cluster without having to manually go to each machine and update their config files with new node's id and ip:port entry?
Can someone please help? Thanks!
If you want to start a new ZooKeeper server process from your Java code, you would do it the same way you would start any other external process from Java, e.g. using a ProcessBuilder. There is nothing special here in case of ZooKeeper. You can check the official docs on how the actual command should look like. It gets complicated if you want to supervise the process for production use, so in that case it would be better to use something provided on your OS (e.g. upstart, runit, etc...), or take a look at Exhibitor for code examples: https://github.com/Netflix/exhibitor.
If you are asking about starting a ZooKeeper cluster from your Java program, then you complicate things further, since you would basically need to supervise multiple ZooKeeper JVM processes on different hosts. Also take a look at Exhibitor.
If your question is about starting a ZooKeeper server instance inside the same JVM process as your Java code (embedded), then it is also possible. There are a few important details to keep in mind, take a look at this answer: Is it possible to start a zookeeper server instance in process, say for unit tests?
Regarding your second question, real support for dynamic cluster reconfiguration was added just recently, in 3.5.0: http://zookeeper.apache.org/doc/trunk/zookeeperReconfig.html.
Prior to this, you can still "add servers to zookeeper cluster without having to manually go to each machine and update their config", but you have to use a configuration management tool like Chef, Puppet or similar, and in this case you would also need to do a restart of the cluster to uptake new config.
