question

I would try running the Experimenter (rather than the optimizer) first. Note that if you have lots of instances set up, it can take a long time (like 120 seconds or more) to actually start running replications, once you click the Run Experiment button.

If you can do an Experiment, then you should be able to do an Optimization. If you can't do an experiment, then be sure to double check each of the steps in the article you linked. If Amazon's interface has changed, then maybe we'll need to update the article. But, as far as I know, FlexSim's steps haven't changed at all.

It is difficult to provide an example, because so much depends on your server configuration. Most issues are with server/network configuration, not with FlexSim itself.

One way to test whether the distributed cores feature is working for you at all is to use localhost as one of your remote nodes. Just be sure that the webserver is running on your local machine. If that works, then you know that the distributed cores feature works.

To test the instances, try to go to the webserver running on each instance (which you need to do anyways to use distributed CPUs). If you can't get the webserver page, then you won't be able to run an experiment on that machine, either.