# Hosting multiple organizations¶

The vast majority of Zulip servers host just a single organization (or “realm”, as the Zulip code calls organizations). This article documents what’s involved in hosting multiple Zulip organizations on a single server.

Throughout this article, we’ll assume you’re working on a Zulip server with hostname zulip.example.com. You may also find the more technically focused article on realms to be useful reading.

## Subdomains¶

Zulip’s approach for supporting multiple organizations on a single Zulip server is for each organization to be hosted on its own subdomain. E.g. you’d have org1.zulip.example.com and org2.zulip.example.com.

Web security standards mean that one subdomain per organization is required to support a user logging into multiple organizations on a server at the same time.

When you want to create a new organization, you need to do a few things:

• If you’re using Zulip older than 1.7, you’ll need to set REALMS_HAVE_SUBDOMAINS=True in your /etc/zulip/settings.py file. That setting is the default in 1.7 and later.

• Make sure you have SSL certificates for all of the subdomains you’re going to use. If you’re using our Let’s Encrypt instructions, it’s easy to just specify multiple subdomains in your certificate request.

• If necessary, modify your nginx configuration to use your new certificates.

• Use ./manage.py generate_realm_creation_link again to create your new organization. Review the install instructions if you need a refresher on how this works.

• If you’re planning on using GitHub auth or another social authentication method, review the notes on SOCIAL_AUTH_SUBDOMAIN below.

For servers hosting a large number of organizations, like zulip.com, one can set ROOT_DOMAIN_LANDING_PAGE = True in /etc/zulip/settings.py so that the homepage for the server is a copy of the Zulip homepage.

### SSL certificates¶

You’ll need to install an SSL certificate valid for all the (sub)domains you’re using your Zulip server with. You can get an SSL certificate covering several domains for free by using our Certbot wrapper tool, though if you’re going to host a large number of organizations, you may want to get a wildcard certificate. You can also get a wildcard certificate for free using Certbot, but because of the stricter security checks for acquiring a wildcard cert, it isn’t possible for a generic script like setup-certbot to create it for you; you’ll have to do some manual steps with your DNS provider.

### Other hostnames¶

If you’d like to use hostnames that are not subdomains of each other, you can set the REALM_HOSTS setting in /etc/zulip/settings.py to a Python dictionary, like this:

REALM_HOSTS = {
'mysubdomain': 'hostname.example.com',
}


What this will do is map the hostname hostname.example.com to the realm whose subdomain in the Zulip database is mysubdomain.

In a future version of Zulip, we expect to move this configuration into the database.

### The root domain¶

Most Zulip servers host a single Zulip organization on the root domain (e.g. zulip.example.com). The way this is implemented internally involves the organization having the empty string ('') as its “subdomain”.

You can mix having an organization on the root domain and some others on subdomains (e.g. subdivision.zulip.example.com), but this only works well if there are no users in common between the two organizations, because the auth cookies for the root domain are visible to the subdomain (so it’s not possible for a single browser/client to be logged into both). So we don’t recommend that configuration.

### Authentication¶

Many of Zulip’s supported authentication methods (Google, GitHub, SAML, etc.) can require providing the third-party authentication provider with a whitelist of callback URLs to your Zulip server (or even a single URL). For those vendors that support a whitelist, you can provide the callback URLs for each of your Zulip organizations.

The cleaner solution is to register a special subdomain, e.g. auth.zulip.example.com with the third-party provider, and then set SOCIAL_AUTH_SUBDOMAIN = 'auth' in /etc/zulip/settings.py, so that Zulip knows to use that subdomain for these authentication callbacks.

### The system bot realm¶

This is very much an implementation detail, but worth documenting to avoid confusion as to why there’s an extra realm when inspecting the Zulip database.

Every Zulip server comes with 1 realm that isn’t created by users: the zulipinternal realm. By default, this realm only contains the Zulip “system bots”. You can get a list of these on your system via ./scripts/get-django-setting INTERNAL_BOTS, but this is where bots like “Notification Bot”, “Welcome Bot”, etc. exist. In the future, we’re considering moving these bots to exist in every realm, so that we wouldn’t need the system realm anymore.

### Migrating / troubleshooting¶

If you’re migrating from a configuration using the root domain to one with realms hosted on subdomains, be sure to clear cookies in any browsers that were logged in on the root domain; otherwise, those browsers will experience weird/confusing redirects.