Wafflehaus is a collection of WSGI middleware for OpenStack that adds functionality with zero impact to code.
Each middleware is lovingly called a waffle.
Cloud providers of all sizes have problems dealing with business-requirements of their cloud and diverging from upstream. By putting business logic into middleware providers can create special cases without changing upstream code.
Not diverging from upstream is wonderful because:
- You do not need to handle merge conflicts
- The review process for wafflehaus is shorter especially if you fork it
- Although your requirement may not benefit OpenStack as a whole, it still fits in Wafflehaus
Beyond the above benefits, other benefits of using wafflehaus are:
- You gain access to plenty of predefined waffles that can usually be configured to support your special case
- All of the waffles in wafflehaus are designed to be configured in the api-paste.ini file and thus can be distributed however you wish (puppet, chef, ansible)
- It is a fairly democratic and simple way to test new openstack features and designs as if many people use a particular waffle it should be added to the relevant projects' feature set
Finally, although Wafflehaus was intended to work with OpenStack, it is possible to use it in front of any WSGI compliant service.
The official channel for wafflehaus support in on freenode in #wafflehaus.
Using wafflehaus is simple! A stable version is available on pypi but you can always install wafflehaus using pip+git. Modify your api-paste.ini to include your waffle of choice and add the waffle where you wish in the composite that defines your app.
Example using dns_filter:
[composite:neutronapi_v2_0]
use = call:neutron.auth:pipeline_factory
noauth = dns_filter request_id catch_errors extensions neutronapiapp_v2_0
keystone = dns_filter request_id catch_errors authtoken keystonecontext
extensions neutronapiapp_v2_0
# This is the waffle
[filter:dns_filter]
paste.filter_factory = wafflehaus.dns_filter.whitelist:filter_factory
whitelist = mydomain.com
# Uncomment the line below to activate the waffle
# enabled = true
Then restart the service (or SIGHUP if it applies). If you have an error in your configuration you'll see it in your logs very early, fix that and you'll be rolling.
Note: All waffles are disabled until explicitly set to enabled with the enabled = true configuration flag. This allows you to deploy a waffle without concerns (beyond configuration being correct or not).
It is difficult to test wafflehaus in CI environments because of how PasteDeploy works. The server will need to be restarted for new configurations (api-paste) to be loaded. Runtime reconfiguring allows you to change the configurations using headers. Each waffle that wants to support this will need to override the WafflehausBase:_override method, and will need to call the base's __call__.
Finally to enable this the global configuration (nova.conf, neutron.conf) needs to have the following:
[WAFFLEHAUS] runtime_reconfigurable = True
All waffles that, at a minimum, call the base's __call__ will support runtime enable/disable and toggling of testing with the following headers:
- X_WAFFLEHAUS_CLASSNAME_ENABLED
- X_WAFFLEHAUS_CLASSNAME_TESTING
where CLASSNAME is the upper() of the class name of the waffle.
Right now all the subprojects do not include wafflehaus in their requirements file. This is because of weird quirks we have been happening while deploying wafflehaus' subprojects. We are working to get those fixed but please do note: the subprojects do require wafflehaus to be installed.
- Typical github-etiquette expected
- Conform to the guidelines below
- Provide a solution in its most shareable form
- Add reusuable functionality to wafflehaus as a whole (see resource_filter)
- Do not configure in code; configure from external files
- Do not depend on specific OpenStack projects
- If you must depend on a specific OpenStack project, look for the corresponding wafflehaus subproject
- Each package should have a README.rst
- Provide an example use-case of your middleware in the documentation
- Do not raise exceptions, return them
- Do not assume any other waffle exists if you can; document if you can't
- Readable code is preferred over clever code
The reason why exceptions are returned instead of raised is due to interactions with eventlet. When an exception is raised it causes eventlet to halt so it can process the exception.
This has certain interactions with faultwrapper because it only catches raised exceptions. If you rely on faultwrapper then you may raise the exception or, if you are using a subproject that has access to it, you may do the following:
from nova.api.openstack import wsgi
return wsgi.Fault(your_exception)
In this situation the waffle would be in the wafflehaus.nova subproject (as it makes use of nova libraries).
In some situations it is impossible to completely ignore a dependency on a project. In those situations there are subprojects for those dependencies:
If a subproject is not listed here it may still exist. Also new ones can be made at any time.