Readme about how to add Integrations and Zabbix Integration (#653)

* Readme and zabbix

* Typos

* Linking

DEVELOPER.md

@@ -20,6 +20,8 @@
 
 ## Developer quickstart
 
+Related: [How to develop integrations](/engine/config_integrations/README.md)
+
 ### Code style
 
 - [isort](https://github.com/PyCQA/isort), [black](https://github.com/psf/black) and [flake8](https://github.com/PyCQA/flake8) are used to format backend code

README.md

@@ -87,5 +87,6 @@ See [Grafana docs](https://grafana.com/docs/grafana/latest/administration/plugin
 
 - _Migration from the PagerDuty_ - [Migrator](https://github.com/grafana/oncall/tree/dev/tools/pagerduty-migrator)
 - _Documentation_ - [Grafana OnCall](https://grafana.com/docs/grafana-cloud/oncall/)
+- _How To Add Integration_ - [How to Add Integration](https://github.com/grafana/oncall/tree/dev/engine/config_integrations/README.md)
 - _Blog Post_ - [Announcing Grafana OnCall, the easiest way to do on-call management](https://grafana.com/blog/2021/11/09/announcing-grafana-oncall/)
 - _Presentation_ - [Deep dive into the Grafana, Prometheus, and Alertmanager stack for alerting and on-call management](https://grafana.com/go/observabilitycon/2021/alerting/?pg=blog)

engine/config_integrations/README.md

@@ -0,0 +1,21 @@
+# Contribute the new Integration to OnCall
+
+Related: [DEVELOPER.md](/DEVELOPER.md)
+
+"Integration" in OnCall is a pre-configured webhook for alert consumption from alert sources. Usually, alert sources are monitoring systems such as Grafana or Zabbix.
+
+Integration is a set of "templates" which are dumped from the integration config once the integration is created. Further changes to "templates" don't reflect on the integration config. Read more about templates [here](https://grafana.com/docs/oncall/latest/integrations/create-custom-templates/).
+
+This instruction is supposed to help you to build templates to integrate OnCall with a new source of alerts. If you don't want to contribute to OnCall and are looking for a help integrating with custom alert source as a user, refer to [this](https://grafana.com/docs/oncall/latest/integrations/create-custom-templates/) instruction.
+
+# Files related to Integrations
+0. Refer to "Grafana" integration as the most complete example.
+1. Each integration should have a `{{integration_name_in_snake_case}}.py` file in `/engine/config_integrations`. There you'll find Templates that will be copied to the Integration Templates once the integration is created by the user in the OnCall UI; Example Payload; and Tests which should match the result of the rendering of Example Payload as using Templates. The best way to build such a file is to create Webhook Integration, write & debug templates in the UI first and copy-paste them to the file after.
+2. Each integration should be listed in the `/engine/settings/base.py` file, section `INSTALLED_ONCALL_INTEGRATIONS`.
+3. Each integration should have "How to connect" instruction stored as `integration_{{integration_name_in_snake_case}}.html` in the `engine/apps/integrations/html` folder. `.py` file has a `slug` field that is used to locate `.html` file.
+
+# What do we expect from high-quality integration?
+
+1. User-friendly integration instruction.
+2. Proper grouping following source's logics. If source generates multiple alerts per "detection" it would be nice to provide suitable grouping & resolving configuration in the templates.
+3. Awesome rendering. We all love when alerts look good in Slack, SMS and all other rendering destinations.

engine/config_integrations/zabbix.py

@@ -0,0 +1,62 @@
+# Main
+enabled = True
+title = "Zabbix"
+slug = "zabbix"
+short_description = None
+description = None
+is_displayed_on_web = True
+is_featured = False
+is_able_to_autoresolve = True
+is_demo_alert_enabled = True
+
+description = None
+
+# Default templates
+slack_title = """\
+*<{{ grafana_oncall_link }}|#{{ grafana_oncall_incident_id }} {{ payload.get("title", "Title undefined (check Slack Title Template)") }}>* via {{ integration_name }}
+{% if source_link %}
+ (*<{{ source_link }}|source>*)
+{%- endif %}"""
+
+slack_message = '{{ payload.get("message", "") }}'
+
+slack_image_url = '{{ payload.get("image_url", "") }}'
+
+web_title = '{{ payload.get("title", "Title undefined (check Web Title Template)") }}'
+
+web_message = slack_message
+
+web_image_url = slack_image_url
+
+sms_title = web_title
+
+phone_call_title = sms_title
+
+email_title = web_title
+
+email_message = web_message
+
+telegram_title = sms_title
+
+telegram_message = slack_message
+
+telegram_image_url = slack_image_url
+
+source_link = "{{ payload.link_to_upstream_details }}"
+
+grouping_id = '{{ payload.get("alert_uid", "")}}'
+
+resolve_condition = '{{ payload.get("state", "").upper() == "OK" }}'
+
+acknowledge_condition = None
+
+group_verbose_name = web_title
+
+example_payload = {
+    "alert_uid": "08d6891a-835c-e661-39fa-96b6a9e26552",
+    "title": "TestAlert: The whole system is down",
+    "image_url": "https://upload.wikimedia.org/wikipedia/commons/e/ee/Grumpy_Cat_by_Gage_Skidmore.jpg",
+    "state": "alerting",
+    "link_to_upstream_details": "https://en.wikipedia.org/wiki/Downtime",
+    "message": "This alert was sent by user for the demonstration purposes\nSmth happened. Oh no!",
+}

engine/settings/base.py

@@ -586,6 +586,7 @@ INSTALLED_ONCALL_INTEGRATIONS = [
     "config_integrations.maintenance",
     "config_integrations.manual",
     "config_integrations.slack_channel",
+    "config_integrations.zabbix",
 ]
 
 if OSS_INSTALLATION: