Hi Paul,
In the original post, Bryson said he is using Server 10.2, which would imply he is also using Portal 10.2. This was the first COTS release of Portal and in that release, our documentation said it was possible to use a single Web Adaptor for both Server and Portal. Since the 10.2 release, we've learned that it is not good to use a single Web Adaptor for both. So, in order to NOT contradict the 10.2 help documentation, I used the term "best practice".
> I thought it was required that if using a Web Adaptor (WA) with both Portal and ArcGIS Server (AGS) that you had to use two independent WAs. True?
Yes, you are correct. And in post 10.2 Server releases, the help doc says this.
> You don't have to use a WA except in some settings, such as federation, reverse proxy, DMZ usage or NLB. True?
The Web Adaptor is optional for ArcGIS Server (aka. GIS Server). The Web Adaptor is required for Portal for ArcGIS to work.
> Regarding your comment about best practice: does that mean you can run Portal and AGS on one WA but its not recommended ...
Incorrect. Please see my opening statements above - referring back to the 10.2 Server and Portal help documentation.
> ... or are you saying that you could run AGS on a WA and Portal with out a WA (or vice versa) but that the latter setup of only one server using a WA is not considered best practice?
The first statement is false and incorrect. The second option: Portal for ArcGIS with Web Adaptor + GIS Server without a Web Adaptor is a possible deployment option, it depends on your business requirements.
> I will always set it up with two independent WAs and just thought that was required if you want to use a WA. It's easy enough to install a second one and the overhead seems fairly minimal.
I always do the same. Keeps the Web GIS deployment "simple".
Hope this helps,
Derek