First, create the stream you'd like to use for Nagios notifications, and subscribe all interested parties to this stream. The integration will use the default stream nagios if no stream is supplied in the configuration; you still need to create the stream even if you are using this default.

Next, download and install our Python bindings and example scripts on your Nagios server.

Next, open integrations/nagios/zuliprc.example in your favorite editor, and change the following lines to specify the email address and API key for your Nagios bot, saving it to /etc/nagios3/zuliprc on your Nagios server:

[api]
email = NAGIOS_BOT_EMAIL_ADDRESS
key = NAGIOS_BOT_API_KEY
{% if api_site_required %}site = {{ external_api_uri_subdomain }}{% endif %}

Copy integrations/nagios/zulip_nagios.cfg to /etc/nagios3/conf.d on your Nagios server.

Finally, add zulip to the members list for one or more of the contact groups in the CONTACT GROUPS section of /etc/nagios3/conf.d/contacts.cfg, doing something like:

define contactgroup {
    contactgroup_name       admins
    alias                   Nagios Administrators
    members                 monitoring, zulip
}

Congratulations! You're done!
When your Nagios system makes an alert, you'll see a message like the following, to the stream nagios (to change this, edit the arguments to nagios-notify-zulip in /etc/nagios3/conf.d/zulip_nagios.cfg) with a topic indicating the service with an issue:

Testing
If you have external commands enabled in Nagios, you can generate a test notice from your Nagios instance by visiting using the Send custom service notification command in the Service Commands section of any individual service's page on your Nagios instance.

Troubleshooting
You can confirm whether you've correctly configured Nagios to run the Zulip plugin by looking for SERVICE NOTIFICATION lines mentioning zulip in /var/log/nagios3/nagios.log. You can confirm whether you've configured the Zulip plugin code correctly by running /usr/local/share/zulip/integrations/nagios/nagios-notify-zulip directly.