I think that concurrent sessions to the web server are more important than concurrent users, especially if you have auto page refresh set to a low value. With auto page refresh, one user that leaves a lot of browser tabs open all day can really hammer the server. I saw a big improvement in the user experience by increasing the page refresh interval to 60 mins.
You can poll OID 18.104.22.168.4.1.322.214.171.124.1.13 on your solarwinds web server to see concurrent sessions in IIS.
So I was asked in a PM how did I set this up. I did this though orion UDP (pictured below,) then added a universal device poller chart to my orion's node summary page (botom pic.) I hope this helps.
To understand this a bit better, you really have to think of how the different parts of the program work. The polling engine is an application all on its own that runs constantly on your system, this is one of the bigger loads on most SW systems.
The web interface that people log into, is a series of programs that execute, return some info (ie: the web page) and then stop running. So lets say one of your users logs in once a day to do a simple report, they would really only consume resources while that report was generating. Another user, a network engineer, might be constantly watching the main page to see whats broken and actively going into nodes to see whats up and such. He will be using the server quite a bit. The screen in your NOC that rotates through 5 pages every minute, they're only active once a minute while each page is generating.
I'm trying to impress how transient web transactions can be, that saying it will support 20 users is just a guestimate based on an average server with average use. If you have mostly light users, you might be able to get substantially more users. On the other hand if you have a bunch of users who are always active, or a bunch of pages being displayed that consume a lot of processing power to generate, you might get less than 20 users.
Putting a hard limit on something like this is nearly impossible. So what do you do? Monitor your server in Solarwinds! Maybe enable the "Quality of Experience Application Stats" on the HTTP service. Watch how your server is doing serving up pages and if you start seeing problems, add on an AWS to compensate. Hint, if you add an AWS, have all users use it as the main server to offload your polling engine, cheap way of getting some extra power on the poller...
The primary polling engine and website should support 15-20 concurrent users of the website. Above this you should consider using the optional "Additional Website" which would offload the CPU overhead from the Primary Polling Engine.
it always depends on the Ad Web machine configuration and type of operations(e.g. speed of browsing, which resources are displaying, used limitations), but from my experience the machine, which is strong enough (8 Core, 8GB RAM) should be able to handle ~20 users (acceptable user experience, of course the higher the load is, the slower the website might be).
You could review IIS logs for that info. Within inetpub folder (review your IIS settings for where you should expect to find your logs if necessary).
\some_drive\inetpub\logs\LogFiles\W3SVC2\ in my environment. Yours may be similar.
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