django-watchman

django-watchman exposes a status endpoint for your backing services like databases, caches, etc.

Documentation

The full documentation is at http://django-watchman.rtfd.org.

Testimonials

We're in love with django-watchman. External monitoring is a vital part of our service offering. Using django-watchman we can introspect the infrastructure of an application via a secure URL. It's very well written and easy to extend. We've recommended it to many of our clients already.

— Hany Fahim, CEO, VM Farms.

Quickstart

1. Install django-watchman:

   pip install django-watchman
   

2. Add watchman to your INSTALLED_APPS setting like this:

   INSTALLED_APPS = (
       ...
       'watchman',
   )
   

3. Include the watchman URLconf in your project urls.py like this:

   url(r'^watchman/', include('watchman.urls')),
   

4. Start the development server and visit http://127.0.0.1:8000/watchman/ to get a JSON response of your backing service statuses:

   {
       "databases": [
           {
               "default": {
                   "ok": true
               }
           }
       ],
       "caches": [
           {
               "default": {
                   "ok": true
               }
           }
       ],
       "storage": {"ok": true}
   }
   

Pycon Canada Presentation (10 minutes)

Features

Token based authentication

If you want to protect the status endpoint, you can add a WATCHMAN_TOKEN to your settings. When this setting is added, you must pass that value in as the watchman-token GET parameter:

GET http://127.0.0.1:8000/watchman/?watchman-token=:token

Or by setting the Authorization: WATCHMAN-TOKEN header on the request:

curl -X GET -H "Authorization: WATCHMAN-TOKEN Token=\":token\"" http://127.0.0.1:8000/watchman/

If you want to change the token name, you can set the WATCHMAN_TOKEN_NAME. The value of this setting will be the GET parameter that you must pass in:

WATCHMAN_TOKEN_NAME = 'custom-token-name'

GET http://127.0.0.1:8000/watchman/?custom-token-name=:token

Custom authentication/authorization

If you want to protect the status endpoint with a customized authentication/authorization decorator, you can add WATCHMAN_AUTH_DECORATOR to your settings. This needs to be a dotted-path to a decorator, and defaults to watchman.decorators.token_required:

WATCHMAN_AUTH_DECORATOR = 'django.contrib.admin.views.decorators.staff_member_required'

Note that the token_required decorator does not protect a view unless the WATCHMAN_TOKEN is set in settings.

Custom checks

django-watchman allows you to customize the checks which are run by modifying the WATCHMAN_CHECKS setting. In settings.py:

WATCHMAN_CHECKS = (
    'module.path.to.callable',
    'another.module.path.to.callable',
)

Checks take no arguments, and must return a dict whose keys are applied to the JSON response. Use the watchman.decorators.check decorator to capture exceptions:

from watchman.decorators import check

@check
def my_check():
    return {'x': 1}

In the absence of any checks, a 404 is thrown, which is then handled by the json_view decorator.

Run a subset of available checks

A subset of checks may be run, by passing ?check=module.path.to.callable&check=... in the request URL. Only the callables given in the querystring which are also in WATCHMAN_CHECKS should be run, eg:

curl -XGET http://127.0.0.1:8080/watchman/?check=watchman.checks.caches

Skip specific checks

You can skip any number of checks, by passing ?skip=module.path.to.callable&skip=... in the request URL. Only the checks in WATCHMAN_CHECKS which are not in the querystring should be run, eg:

curl -XGET http://127.0.0.1:8080/watchman/?skip=watchman.checks.email

Django management command

You can also run your checks without starting the webserver and making requests. This can be useful for testing your configuration before enabling a server, checking configuration on worker servers, etc. Run the management command like so:

python manage.py watchman

By default, successful checks will not print any output. If all checks pass successfully, the exit code will be 0. If a check fails, the exit code will be 1, and the error message including stack trace will be printed to stderr.

If you'd like to see output for successful checks as well, set verbosity to 2 or higher:

python manage.py watchman -v 2
{"storage": {"ok": true}}
{"caches": [{"default": {"ok": true}}]}
{"databases": [{"default": {"ok": true}}]}

If you'd like to run a subset of checks, use -c and a comma-separated list of python module paths:

python manage.py watchman -c watchman.checks.caches,watchman.checks.databases -v 2
{"caches": [{"default": {"ok": true}}]}
{"databases": [{"default": {"ok": true}}]}

If you'd like to skip certain checks, use -s and a comma-separated list of python module paths:

python manage.py watchman -s watchman.checks.caches,watchman.checks.databases -v 2
{"storage": {"ok": true}}

Use -h to see a full list of options:

python manage.py watchman -h

Custom response code

By default, watchman will return a 200 HTTP response code, even if there's a failing check. You can specify a different response code for failing checks using the WATCHMAN_ERROR_CODE setting:

WATCHMAN_ERROR_CODE = 500

Available checks

caches

For each cache in django.conf.settings.CACHES:

• Set a test cache item
• Get test item
• Delete test item

databases

For each database in django.conf.settings.DATABASES:

• Verify connection by calling connections[database].introspection.table_names()

email

Send a test email to [email protected] using django.core.mail.send_mail.

If you're using a 3rd party mail provider, this check could end up costing you money, depending how aggressive you are with your monitoring. For this reason, this check is not enabled by default.

For reference, if you were using Mandrill, and hitting your watchman endpoint once per minute, this would cost you ~$5.60/month.

Custom Settings

• WATCHMAN_EMAIL_RECIPIENTS (default: [[email protected]]): Specify a list of email addresses to send the test email
• WATCHMAN_EMAIL_HEADERS (default: {}): Specify a dict of custom headers to be added to the test email

storage

Using django.core.files.storage.default_storage:

• Write a test file
• Check the test file's size
• Read the test file's contents
• Delete the test file

Default checks

By default, django-watchman will run checks against your databases (watchman.checks.databases), caches (watchman.checks.caches), and storage (watchman.checks.storage).

Paid checks

Currently there is only one "paid" check - watchman.checks.email. You can enable it by setting the WATCHMAN_ENABLE_PAID_CHECKS to True, or by overriding the WATCHMAN_CHECKS setting.

Trying it out with Vagrant

A sample project is available along with a Vagrantfile to make it easy to try out django-watchman.

Requirements

• Vagrant
• Virtualbox
• Ansible

Instructions

1. Launch vagrant box: vagrant up
2. SSH into vagrant: vagrant ssh
3. Activate the virtualenv: workon watchman
4. Launch the development server: python manage.py runserver 0.0.0.0:8000
5. Visit watchman json endpoint in your browser: http://127.0.0.1:8000/watchman/
6. Visit watchman dashboard in your browser: http://127.0.0.1:8000/watchman/dashboard/