Whats the best way to load test?

Question

So our app is ready for prime time and we are concerned about response times whether we will survive 100 simultaneous users.
It would be additionally useful if I knew how many users we could tolerate simulataneously.
I attempted running jmeter but I didn't spend a lot of time with it and it didn't overwhelm me with information.
I get the sense that I would probably have to spend a couple weeks to really create useful, valid test simulations which I didn't have time for.
Also, is it even legitimate? The fact that it is one single machine trying to simulate a hundred users on distributed machines?
So, I really lacked a lot of confidence in my test.
In fantasyland it would be great, if say there were some distributed google cloud machines that could simulate 100 users and start firing away at my app.
Starting at 10 users and ramping up until no longer responsive and then providing those results.
The fact is I don't have a lot of experience with this and would appreciate insight.
Also, it just occurred to me that this is an internal app inaccessible from outside the organization.
Does anyone have something they might consider the holy grail of load testing or good advice? Thx.

Answer 1

If you have money to spend, I would recommend using Oracle's Application Test Suite (ATS) since it is the only test tool I know of that allows you to create a functional test and then convert it to a load test. The capabilities of this tool are pretty amazing considering that it is a single tool where the go to toolset in the past was Win Runner / Load Runner. With Win Runner, you needed 50 machines (or VMs) if you wanted to generate front end load for 50 users. With ATS, you record a script with your browser, and then convert it into a load test. You can adjust things like think time, ramp up time, sustained load, etc.
What a lot of people miss is that testing tools can be used indefinitely, not just for getting through a migration. If you script your tests appropriately (which means that your user base trusts them), you can use them for every code release because it takes very little effort to run a test script. On top of that, you can set up strategically placed machines around your network that are set up to run a specific test script (think of a common transaction) so that performance metrics can be captured. I worked for a company that had 160 locations around the world and we used our testing tool as a performance monitor in the locations with the worst performance. Having a tool allowed us to see whether our performance issues were related to network, database, app servers, etc. This took the burden of explaining performance issues off of the users. Most users can't really articulate what the problems are anyway (and they aren't expected to).
If budget is an issue, you can use JMeter from Apache, which will give you the load testing capability but you will miss out on the excellent reporting and management capabilities of the Oracle Application Test Suite.