Want to deploy to servers in parallel using Groovy - multithreading

Question

I am trying to Deploy to a list of servers in parallel to save some time. The names of servers are listed in a collection: serverNames
The original code was:
serverNames.each({
def server = new Server([steps: steps, hostname: it, domain: "test"])
server.stopTomcat()
server.ssh("rm -rf ${WEB_APPS_DIR}/pc*")
PLMScriptUtils.secureCopy(steps, warFileLocation, it, WEB_APPS_DIR)
})
Basically i want to stop the tomcat, rename a file and then copy a war file to a location using the following lines:
server.stopTomcat()
server.ssh("rm -rf ${WEB_APPS_DIR}/pc*")
PLMScriptUtils.secureCopy(steps, warFileLocation, it, WEB_APPS_DIR)
The original code was working properly and it took 1 server from the collection serverNames and performed the 3 line to do the deploy.
But now i have requirement to run the deployment to the servers listed in serverNames parallely
Below is my new modified code:
def threads = []
def th
serverNames.each({
def server = new Server([steps: steps, hostname: it, domain: "test"])
th = new Thread({
steps.echo "doing deployment"
server.stopTomcat()
server.ssh("rm -rf ${WEB_APPS_DIR}/pc*")
PLMScriptUtils.secureCopy(steps, warFileLocation, it, WEB_APPS_DIR)
})
threads << th
})
threads.each {
steps.echo "joining thread"
it.join()
}
threads.each {
steps.echo "starting thread"
it.start()
}
The echo statements were added to visualize the flow.
With this the output is coming as:
joining thread
joining thread
joining thread
joining thread
starting thread
starting thread
starting thread
starting thread
The number of servers in the collection was 4 hence 4 times the thread is being added and started. but it is not executing the 3 lines i want to run in parallel, which means "doing deployment" is not being printed at all and later the build is failing with an exception.
Note that i am running this Groovy code as a pipeline through Jenkins this whole piece of code is actually a function called deploy of the class deployment and my pipeline in jenkins is creating an object of the class deployment and then calling the deploy function
Can anyone help me with this ? I am stuck like hell with this one. :-(

Answer 1

Have a look at the parallel step. In scripted pipelines (which you seem to be using), you can pass it a map of thread name to action (as a Groovy closure) which is then run in parallel.
deployActions = [
Server1: {
// stop tomcat etc.
},
Server2: {
...
}
]
parallel deployActions
It is much simpler and the recommended way of doing it.