# Realms in Zulip

Zulip allows multiple *realms* to be hosted on a single instance.
Realms are the Zulip codebases's internal name for what we refer to in
user documentation as an organization (the name "realm" comes from
[Kerberos](https://web.mit.edu/kerberos/)).

## Creating Realms

There are two main methods for creating realms.

* Using unique link generator
* Enabling open realm creation

#### Using Unique Link Generator

```bash
    ./manage.py generate_realm_creation_link
```

The above command will ouput a URL which can be used for creating a
new realm and an administrator user for that realm. The link expires
after the creation of the realm.  The link also expires if not used
within 7 days. The expiration period can be changed by modifying
`REALM_CREATION_LINK_VALIDITY_DAYS` in settings.py.

### Enabling Open Realm Creation

If you want anyone to be able to create new realms on your server, you
can enable Open Realm Creation.  This will add a **Create new
organization** link to your Zulip homepage footer, and anyone can
create a new realm by visiting this link (**/create_realm**).  This
feature is disabled by default in production instances, and can be
enabled by setting `OPEN_REALM_CREATION = True` in settings.py.

## Subdomains

A reasonable way to deploy a multi-realm Zulip server in production is
to give each realm a unique subdomain. For example if the Zulip
instance is hosted at zulip.example.com and the subdomain of your
organization is acme you can use acme.zulip.example.com for accessing
the organization.  This subdomain feature is not enabled by default,
since it requires additional DNS configuration. You can enable
subdomains by setting the value of `REALMS_HAVE_SUBDOMAINS` to True in
settings.py. For subdomains to work properly, you also have to change
your DNS records so that the subdomains point to your Zulip
installation IP. An `A` record with host name value `*` pointing to
your IP should do the job.

Converting a production Zulip server from not using subdomains to
using subdomains requires some setup work; contact the Zulip
development community for help with this.

### Working With Subdomains In Development Evironment

By default, Linux does not provide a convenient way to use subdomains
in your local development environment.  To solve this problem, we use
the **zulipdev.com** domain, which has a wildcard A record pointing to
127.0.0.1. When `REALMS_HAVE_SUBDOMAINS = True` in
`zproject/dev_settings.py`, you should use zulipdev.com to connect to
your Zulip development server instead of localhost. The default realm
with the Shakespeare users has the subdomain `zulip` and can be
accessed by visiting **zulip.zulipdev.com**.

If you are behind a **proxy server**, this method won't work. When you
make a request to load zulipdev.com in your browser, the proxy server
will try to get the page on your behalf.  Since zulipdev.com points
to 127.0.0.1 the proxy server is likely to give you a 503 error.  The
workaround is to disable your proxy for `*.zulipdev.com`. The DNS
lookup should still work even if you disable proxy for
*.zulipdev.com. If it doesn't you can add zulipdev.com records in
`/etc/hosts` file. The file should look something like this.

 ```
127.0.0.1    localhost

127.0.0.1    zulipdev.com

127.0.0.1    zulip.zulipdev.com

127.0.0.1    testsubdomain.zulipdev.com
```

These records are also useful if you want to e.g. run the casper tests
when you are not connected to the Internet.