===================
django-health-check
===================

|version| |ci| |coverage| |health| |license|

This project checks for various conditions and provides reports when anomalous
behavior is detected.

The following health checks are bundled with this project:

- cache
- database
- storage
- disk and memory utilization (via ``psutil``)
- AWS S3 storage
- Celery task queue
- RabbitMQ

Writing your own custom health checks is also very quick and easy.

We also like contributions, so don't be afraid to make a pull request.

Use Cases
---------

The primary intended use case is to monitor conditions via HTTP(S), with
responses available in HTML and JSON formats. When you get back a response that
includes one or more problems, you can then decide the appropriate course of
action, which could include generating notifications and/or automating the
replacement of a failing node with a new one. If you are monitoring health in a
high-availability environment with a load balancer that returns responses from
multiple nodes, please note that certain checks (e.g., disk and memory usage)
will return responses specific to the node selected by the load balancer.

Supported Versions
------------------

We officially only support the latest version of Python as well as the
latest version of Django and the latest Django LTS version.

.. note:: The latest version to support Python 2 is 2.4.0

Installation
------------

First install the ``django-health-check`` package:

.. code::

    pip install django-health-check

Add the health checker to a URL you want to use:

.. code:: python

    urlpatterns = [
        # ...
        url(r'^ht/', include('health_check.urls')),
    ]

Add the ``health_check`` applications to your ``INSTALLED_APPS``:

.. code:: python

    INSTALLED_APPS = [
        # ...
        'health_check',                             # required
        'health_check.db',                          # stock Django health checkers
        'health_check.cache',
        'health_check.storage',
        'health_check.contrib.celery',              # requires celery
        'health_check.contrib.psutil',              # disk and memory utilization; requires psutil
        'health_check.contrib.s3boto_storage',      # requires boto and S3BotoStorage backend
        'health_check.contrib.rabbitmq',            # requires RabbitMQ broker
        'health_check.contrib.redis',               # required Redis broker
    ]

(Optional) If using the ``psutil`` app, you can configure disk and memory
threshold settings; otherwise below defaults are assumed. If you want to disable
one of these checks, set its value to ``None``.

.. code:: python

    HEALTH_CHECK = {
        'DISK_USAGE_MAX': 90,  # percent
        'MEMORY_MIN': 100,    # in MB
    }

If using the DB check, run migrations:

.. code::

    django-admin migrate

To use the RabbitMQ healthcheck, please make sure that there is a variable named ``BROKER_URL``
on django.conf.settings with the required format to connect to your rabbit server. For example:

.. code::

    BROKER_URL = amqp://myuser:mypassword@localhost:5672/myvhost

To use the Redis healthcheck, please make sure that there is a variable named ``REDIS_URL``
on django.conf.settings with the required format to connect to your redis server. For example:

.. code::

    REDIS_URL = redis://localhost:6370

Setting up monitoring
---------------------

You can use tools like Pingdom_ or other uptime robots to monitor service status.
The ``/ht/`` endpoint will respond a HTTP 200 if all checks passed
and a HTTP 500 if any of the tests failed.

.. code::

    $ curl -v -X GET -H http://www.example.com/ht/

    > GET /ht/ HTTP/1.1
    > Host: www.example.com
    > Accept: */*
    >
    < HTTP/1.1 200 OK
    < Content-Type: text/html; charset=utf-8

    <!-- This is an excerpt -->
    <div class="container">
        <h1>System status</h1>
        <table>
            <tr>
                <td class="status_1"></td>
                <td>CacheBackend</td>
                <td>working</td>
            </tr>
            <tr>
                <td class="status_1"></td>
                <td>DatabaseBackend</td>
                <td>working</td>
            </tr>
            <tr>
                <td class="status_1"></td>
                <td>S3BotoStorageHealthCheck</td>
                <td>working</td>
            </tr>
        </table>
    </div>

Getting machine readable JSON reports
-------------------------------------

If you want machine readable status reports you can request the ``/ht/``
endpoint with the ``Accept`` HTTP header set to ``application/json``
or pass ``format=json`` as a query parameter.

The backend will return a JSON response:

.. code::

    $ curl -v -X GET -H "Accept: application/json" http://www.example.com/ht/

    > GET /ht/ HTTP/1.1
    > Host: www.example.com
    > Accept: application/json
    >
    < HTTP/1.1 200 OK
    < Content-Type: application/json

    {
        "CacheBackend": "working",
        "DatabaseBackend": "working",
        "S3BotoStorageHealthCheck": "working"
    }

    $ curl -v -X GET http://www.example.com/ht/?format=json

    > GET /ht/?format=json HTTP/1.1
    > Host: www.example.com
    >
    < HTTP/1.1 200 OK
    < Content-Type: application/json

    {
        "CacheBackend": "working",
        "DatabaseBackend": "working",
        "S3BotoStorageHealthCheck": "working"
    }

Writing a custom health check
-----------------------------

Writing a health check is quick and easy:

.. code:: python

    from health_check.backends import BaseHealthCheckBackend

    class MyHealthCheckBackend(BaseHealthCheckBackend):
        #: The status endpoints will respond with a 200 status code
        #: even if the check errors.
        critical_service = False

        def check_status(self):
            # The test code goes here.
            # You can use `self.add_error` or
            # raise a `HealthCheckException`,
            # similar to Django's form validation.
            pass

        def identifier(self):
            return self.__class__.__name__  # Display name on the endpoint.

After writing a custom checker, register it in your app configuration:

.. code:: python

    from django.apps import AppConfig

    from health_check.plugins import plugin_dir

    class MyAppConfig(AppConfig):
        name = 'my_app'

        def ready(self):
            from .backends import MyHealthCheckBackend
            plugin_dir.register(MyHealthCheckBackend)

Make sure the application you write the checker into is registered in your ``INSTALLED_APPS``.

Customizing output
------------------

You can customize HTML or JSON rendering by inheriting from ``MainView`` in ``health_check.views``
and customizing the ``template_name``, ``get``, ``render_to_response`` and ``render_to_response_json`` properties:

.. code:: python

    # views.py
    from health_check.views import MainView

    class HealthCheckCustomView(MainView):
        template_name = 'myapp/health_check_dashboard.html'  # customize the used templates

        def get(self, request, *args, **kwargs):
            plugins = []
            # ...
            if 'application/json' in request.META.get('HTTP_ACCEPT', ''):
                return self.render_to_response_json(plugins, status)
            return self.render_to_response(plugins, status)

        def render_to_response(self, plugins, status):       # customize HTML output
            return HttpResponse('COOL' if status == 200 else 'SWEATY', status=status)

        def render_to_response_json(self, plugins, status):  # customize JSON output
            return JsonResponse(
                {str(p.identifier()): 'COOL' if status == 200 else 'SWEATY' for p in plugins}
                status=status
            )

    # urls.py
    import views

    urlpatterns = [
        # ...
        url(r'^ht/$', views.HealthCheckCustomView.as_view(), name='health_check_custom'),
    ]

Django command
--------------

You can run the Django command `health_check` to perform your health checks via the command line,
or periodically with a cron, as follow:

.. code::

    django-admin health_check

This should yield the following output:

.. code::

    DatabaseHealthCheck      ... working
    CustomHealthCheck        ... unavailable: Something went wrong!

Similar to the http version, a critical error will case the command to quit with the exit code `1`.


Other resources
---------------

- django-watchman_ is a package that does some of the same things in a slightly different way.
- See this weblog_ about configuring Django and health checking with AWS Elastic Load Balancer.

.. |version| image:: https://img.shields.io/pypi/v/django-health-check.svg
   :target: https://pypi.python.org/pypi/django-health-check/
.. |ci| image:: https://api.travis-ci.org/KristianOellegaard/django-health-check.svg?branch=master
   :target: https://travis-ci.org/KristianOellegaard/django-health-check
.. |coverage| image:: https://codecov.io/gh/KristianOellegaard/django-health-check/branch/master/graph/badge.svg
   :target: https://codecov.io/gh/KristianOellegaard/django-health-check
.. |health| image:: https://landscape.io/github/KristianOellegaard/django-health-check/master/landscape.svg?style=flat
   :target: https://landscape.io/github/KristianOellegaard/django-health-check/master
.. |license| image:: https://img.shields.io/badge/license-MIT-blue.svg
   :target: LICENSE

.. _Pingdom: https://www.pingdom.com/
.. _django-watchman: https://github.com/mwarkentin/django-watchman
.. _weblog: https://www.vincit.fi/en/blog/deploying-django-to-elastic-beanstalk-with-https-redirects-and-functional-health-checks/
