Django 1.10 changed the way middleware works, fixing a number of issues and improving performance (eg due to short-circuiting changes, which help with WhiteNoise). However these changes are backwards incompatible, so only take effect when using a new `MIDDLEWARE` option in settings.py. Anything using the old `MIDDLEWARE_CLASSES` setting is run in the old, less performant manner. Before we can just s/MIDDLEWARE_CLASSES/MIDDLEWARE/ in our settings.py, we need to ensure all the middleware we use is actually compatible with the new API. See: https://docs.djangoproject.com/en/1.11/topics/http/middleware/#upgrading-middleware We use the following non-native-Django middleware: * treeherder.middleware.NewRelicMiddleware: -> Will need adjusting: https://github.com/mozilla/treeherder/blob/f7380546f8cf54f3830718575f6bae6b903f4257/treeherder/middleware.py#L54-L61 * treeherder.middleware.CustomWhiteNoise (subclass of WhiteNoise): -> Already compatible (https://github.com/evansd/whitenoise/blob/v3.3.1/whitenoise/middleware.py#L8-L26) * debug_toolbar.middleware.DebugToolbarMiddleware: -> Already compatible (https://github.com/jazzband/django-debug-toolbar/blob/1.8/debug_toolbar/middleware.py#L19-L23) * corsheaders.middleware.CorsMiddleware: -> Already compatible (https://github.com/ottoyiu/django-cors-headers/blob/2.1.0/corsheaders/compat.py#L1-L6) * hawkrest.middleware.HawkResponseMiddleware: -> Will need fixing: https://github.com/kumar303/hawkrest/issues/38#issuecomment-340293738

Commits pushed to master at https://github.com/mozilla/treeherder https://github.com/mozilla/treeherder/commit/d256834a2a1909d77a95164480c88dc4230414af Bug 1412797 - Adapt NewRelicMiddleware for the new middleware API Makes the middleware compatible with the new-style Django middleware API, ready for switching to it in a later commit. See: https://docs.djangoproject.com/en/1.11/topics/http/middleware/#upgrading-middleware https://github.com/mozilla/treeherder/commit/292a2777b80397cecefcd500db6f8dc7123bc878 Bug 1412797 - Adapt HawkResponseMiddleware for the new middleware API Makes the middleware compatible with the new-style Django middleware API, which hasn't yet happened upstream: https://github.com/kumar303/hawkrest/issues/38 https://github.com/mozilla/treeherder/commit/58e6690e645de083f0aa0430b31f02510b57cec2 Bug 1412797 - Switch to Django's new middleware API The old API (`MIDDLEWARE_CLASSES`) has been deprecated in favour of the `MIDDLEWARE` pref. The new API is faster (since it short-circuits) and has more sensible error handling characteristics. See: https://github.com/django/deps/blob/master/final/0005-improved-middleware.rst https://docs.djangoproject.com/en/1.11/topics/http/middleware/#upgrading-middleware Since the new API short-circuits (that is, doesn't run later middleware if an earlier one returns a response), `XFrameOptionsMiddleware` and `CorsMiddleware` must be moved to before the WhiteNoise middleware, to ensure the headers are still set like before - even when WhiteNoise returns early for static content. (Whilst most static content doesn't need CORS headers, `revision.txt` and `contribute.json` do.)