Is it possible to have multiple instances of Discourse but that users can log in to all of them with the same ID info?
Let’s say that I have a forum for multiple cities, city1.domain.com, city2.domain.com, city3.domain.com but that users only have to register once.
Thanks for the help in advance 
It is possible using multisite. For user registration process use SSO provider feature in domain.com and SSO client feature in cities city1.domain.com, city2.domain.com.
Yes, you can do it as @vinothkannans described. It’s not required that you use multisite setup to do it, but it would likely make sense.
I started just such a configuration for a client recently.
In addition to the above answers to your question, you might also want to think twice before setting up separate discourse instances for different cities. See this topic for more on this:
This person is seen to want to convert each category of the same forum into subdomains. What I mean is to have separate discourse for each place! However, I am going to assume this also require lots of server resources!
Nope, a multisite setup requires practically the same resources as a single site with the same aggregate traffic profile.
Wow thanks for that info @mpalmer . I was a worried about this, but I guess it mostly depends on the traffic and not the installation itself. That’s good to know.
This is more of a technical question; My plan is to have different sub instances, but they will all contain the same topics. Except for the main one, that will be used basically as the landing page, resgistration, informational purposes, and links directory to all the other discourses.
Is it possible to create the primary discourse for the forums and then replicate it so that one doesn’t have to re enter the categories names and descriptions over and over?
I appreciate you all taking the time to help me out!
Discourse is not a CMS. Don’t try and use it as one, it will not end well.
Thank you again for taking the time.
Domain Name: army.community
I have been in the military for about seven years now. Military members move a lot, about every three years you get transferred to a different duty station. My idea is to have a community forum where soldiers and family members can share ideas, information, and inquiries about X army post. As well as a simple chat between people that have the same interest in common already, the army. Until now the best, and most common way of doing this is by creating a Facebook page, which usually is set up by an army wife. The main problem with this approach is that since military members get moved so often, once they leave, the administrator loses interest in that particular post, and the page ends up dying. Not to mention the risk of getting your whole community wiped out by Facebook itself.
I want to have something like fortriley.army.Community, fortirwin.army.Community, fortdrum.army.Community etc. which will be for this purpose.
The forums will be mostly community driven. NOT a blog or such. Just fair sharing of information.
Nope. Nothing in your plan would be better served by having separate subdomains. Your plan also doesn’t cover why you’d want the same topics in all of them, nor why you would want to put all the other non-discussion stuff into Discourse.
Sure. The reason for this is that every military installation has its community. For example; the information about the Commissary at Fort Irwin may and most likely will not apply to the information at Fort Riley. These military installations are often massive, and each community has its problems and inquiries. When people are about to move to a different duty station, they usually start researching about that next duty station. Believe it or not, even tho they are all military posts (base), this is not a one fit all kind of thing. Stuff like housing, services, education, etc. Will most likely be different from post to post. Also, many service members choose to live in off-post housing. Therefore information about near bay areas are also important.
By the way, I get what you mean about the other information. The landing page could as well be just a regular static one. Like a welcome page.
You can use categories to keep those things separate. Also, people who are at one base might have been at another, having to leave one site to another will be confusing. Or that’s what people who have been using Discourse for a long time think. If you want separate domains with SSO to a main site, you can do that, but it doesn’t seem like a good idea.
Hmm, You do have a valid point there.
I was thinking this way more because of SEO purpose. Also, in my experience in the military, normally people at one military installation, don’t care much about another installation until they have to move there, and the people helping will normally be the ones who are already stationed at the installation they are moving to. Plus it can get to clustered if I compile everything together.
BTW, I love how easy I can quote something with Discourse. The more I use this forum the more I like it. ha, ha, ha!
I think I might be inclined to start with one site to see how Discourse works. Once you’ve got one site up and running you could try starting a new set of categories for a second site or a second site with the first one as the SSO master.
I’d think that there would be lots of things worth discussing that are similar everywhere.
Useful content and a meaningful category name are going to do a lot more for SEO than putting the post in the domain.
I don’t think “siloizing” your Discourse like that would bring any benefit.
Have a look at our site (forums.jag-lovers.com). We have categories for each specific model family, and common categories. Our site has always been organized this way. I see more “cross pollination” between the categories since we changed to Discourse - on the old system there was a bit of a “circle the wagons” mentality. Discourse’s search, latest topics presentation, and the ease with which users can link to posts in other threads are the only UI changes, and our user base is more or less the same, but people are helping each other across “knowledge domains” more than they used to.
The only benefit from multiple instances would be if you wanted to have category/instance specific moderators… but that means more staff/effort/duplication of moderator tasks.
You could use sub categories (Bragg-schooling, Bragg-social, Bragg-offsite) for base specific content and have a few generic categories (Army Life-Army Wife, Military parenting, hobbies).
Set up a user custom field “Current Posting:” for your users to indicate where they are, and get them to populate “About me” with past postings, and display that on their user cards.
You probably won’t need to move many things around because users post in the “wrong” category.
Using one instance will decrease your moderation effort.
Yes absolutely. I’m so what familiar with how the forum work, I’m already running a forum on it. Not related to this.
Good points there. Thanks you so much for taking the time to write 
this. You have some good ideas. I’ll take a look at your community and grab some pointers from it.
I’m building this community because I genuinely believe it will bring some benefit to the Army military community.