manila/doc/source/contributor/api_microversion_dev.rst
chengebj5238 3a5ea7184a fix http link to https link
Change-Id: I07e1a7ed99a79b774a7a7ba58f407972f3b724c3
2018-12-14 08:33:03 +00:00

322 lines
11 KiB
ReStructuredText

API Microversions
=================
Background
----------
Manila uses a framework we called 'API Microversions' for allowing changes
to the API while preserving backward compatibility. The basic idea is
that a user has to explicitly ask for their request to be treated with
a particular version of the API. So breaking changes can be added to
the API without breaking users who don't specifically ask for it. This
is done with an HTTP header ``X-OpenStack-Manila-API-Version`` which
is a monotonically increasing semantic version number starting from
``1.0``.
If a user makes a request without specifying a version, they will get
the ``DEFAULT_API_VERSION`` as defined in
``manila/api/openstack/api_version_request.py``. This value is currently ``2.0``
and is expected to remain so for quite a long time.
The Nova project was the first to implement microversions. For full
details please read Nova's `Kilo spec for microversions
<https://specs.openstack.org/openstack/nova-specs/specs/kilo/implemented/api-microversions.html>`_
When do I need a new Microversion?
----------------------------------
A microversion is needed when the contract to the user is
changed. The user contract covers many kinds of information such as:
- the Request
- the list of resource urls which exist on the server
Example: adding a new shares/{ID}/foo which didn't exist in a
previous version of the code
- the list of query parameters that are valid on urls
Example: adding a new parameter ``is_yellow`` servers/{ID}?is_yellow=True
- the list of query parameter values for non free form fields
Example: parameter filter_by takes a small set of constants/enums "A",
"B", "C". Adding support for new enum "D".
- new headers accepted on a request
- the Response
- the list of attributes and data structures returned
Example: adding a new attribute 'locked': True/False to the output
of shares/{ID}
- the allowed values of non free form fields
Example: adding a new allowed ``status`` to shares/{ID}
- the list of status codes allowed for a particular request
Example: an API previously could return 200, 400, 403, 404 and the
change would make the API now also be allowed to return 409.
- changing a status code on a particular response
Example: changing the return code of an API from 501 to 400.
- new headers returned on a response
The following flow chart attempts to walk through the process of "do
we need a microversion".
.. graphviz::
digraph states {
label="Do I need a microversion?"
silent_fail[shape="diamond", style="", label="Did we silently
fail to do what is asked?"];
ret_500[shape="diamond", style="", label="Did we return a 500
before?"];
new_error[shape="diamond", style="", label="Are we changing what
status code is returned?"];
new_attr[shape="diamond", style="", label="Did we add or remove an
attribute to a payload?"];
new_param[shape="diamond", style="", label="Did we add or remove
an accepted query string parameter or value?"];
new_resource[shape="diamond", style="", label="Did we add or remove a
resource url?"];
no[shape="box", style=rounded, label="No microversion needed"];
yes[shape="box", style=rounded, label="Yes, you need a microversion"];
no2[shape="box", style=rounded, label="No microversion needed, it's
a bug"];
silent_fail -> ret_500[label="no"];
silent_fail -> no2[label="yes"];
ret_500 -> no2[label="yes [1]"];
ret_500 -> new_error[label="no"];
new_error -> new_attr[label="no"];
new_error -> yes[label="yes"];
new_attr -> new_param[label="no"];
new_attr -> yes[label="yes"];
new_param -> new_resource[label="no"];
new_param -> yes[label="yes"];
new_resource -> no[label="no"];
new_resource -> yes[label="yes"];
{rank=same; yes new_attr}
{rank=same; no2 ret_500}
{rank=min; silent_fail}
}
**Footnotes**
[1] - When fixing 500 errors that previously caused stack traces, try
to map the new error into the existing set of errors that API call
could previously return (400 if nothing else is appropriate). Changing
the set of allowed status codes from a request is changing the
contract, and should be part of a microversion.
The reason why we are so strict on contract is that we'd like
application writers to be able to know, for sure, what the contract is
at every microversion in manila. If they do not, they will need to write
conditional code in their application to handle ambiguities.
When in doubt, consider application authors. If it would work with no
client side changes on both manila versions, you probably don't need a
microversion. If, on the other hand, there is any ambiguity, a
microversion is probably needed.
In Code
-------
In ``manila/api/openstack/wsgi.py`` we define an ``@api_version`` decorator
which is intended to be used on top-level Controller methods. It is
not appropriate for lower-level methods. Some examples:
Adding a new API method
~~~~~~~~~~~~~~~~~~~~~~~
In the controller class::
@wsgi.Controller.api_version("2.4")
def my_api_method(self, req, id):
....
This method would only be available if the caller had specified an
``X-OpenStack-Manila-API-Version`` of >= ``2.4``. If they had specified a
lower version (or not specified it and received the default of ``2.1``)
the server would respond with ``HTTP/404``.
Removing an API method
~~~~~~~~~~~~~~~~~~~~~~
In the controller class::
@wsgi.Controller.api_version("2.1", "2.4")
def my_api_method(self, req, id):
....
This method would only be available if the caller had specified an
``X-OpenStack-Manila-API-Version`` of <= ``2.4``. If ``2.5`` or later
is specified the server will respond with ``HTTP/404``.
Changing a method's behaviour
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In the controller class::
@wsgi.Controller.api_version("2.1", "2.3")
def my_api_method(self, req, id):
.... method_1 ...
@wsgi.Controller.api_version("2.4") # noqa
def my_api_method(self, req, id):
.... method_2 ...
If a caller specified ``2.1``, ``2.2`` or ``2.3`` (or received the
default of ``2.1``) they would see the result from ``method_1``,
``2.4`` or later ``method_2``.
It is vital that the two methods have the same name, so the second of
them will need ``# noqa`` to avoid failing flake8's ``F811`` rule. The
two methods may be different in any kind of semantics (schema
validation, return values, response codes, etc)
A method with only small changes between versions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A method may have only small changes between microversions, in which
case you can decorate a private method::
@api_version("2.1", "2.4")
def _version_specific_func(self, req, arg1):
pass
@api_version(min_version="2.5") # noqa
def _version_specific_func(self, req, arg1):
pass
def show(self, req, id):
.... common stuff ....
self._version_specific_func(req, "foo")
.... common stuff ....
A change in schema only
~~~~~~~~~~~~~~~~~~~~~~~
If there is no change to the method, only to the schema that is used for
validation, you can add a version range to the ``validation.schema``
decorator::
@wsgi.Controller.api_version("2.1")
@validation.schema(dummy_schema.dummy, "2.3", "2.8")
@validation.schema(dummy_schema.dummy2, "2.9")
def update(self, req, id, body):
....
This method will be available from version ``2.1``, validated according to
``dummy_schema.dummy`` from ``2.3`` to ``2.8``, and validated according to
``dummy_schema.dummy2`` from ``2.9`` onward.
When not using decorators
~~~~~~~~~~~~~~~~~~~~~~~~~
When you don't want to use the ``@api_version`` decorator on a method
or you want to change behaviour within a method (say it leads to
simpler or simply a lot less code) you can directly test for the
requested version with a method as long as you have access to the api
request object (commonly called ``req``). Every API method has an
api_version_request object attached to the req object and that can be
used to modify behaviour based on its value::
def index(self, req):
<common code>
req_version = req.api_version_request
if req_version.matches("2.1", "2.5"):
....stuff....
elif req_version.matches("2.6", "2.10"):
....other stuff....
elif req_version > api_version_request.APIVersionRequest("2.10"):
....more stuff.....
<common code>
The first argument to the matches method is the minimum acceptable version
and the second is maximum acceptable version. A specified version can be null::
null_version = APIVersionRequest()
If the minimum version specified is null then there is no restriction on
the minimum version, and likewise if the maximum version is null there
is no restriction the maximum version. Alternatively a one sided comparison
can be used as in the example above.
Other necessary changes
-----------------------
If you are adding a patch which adds a new microversion, it is
necessary to add changes to other places which describe your change:
* Update ``REST_API_VERSION_HISTORY`` in
``manila/api/openstack/api_version_request.py``
* Update ``_MAX_API_VERSION`` in
``manila/api/openstack/api_version_request.py``
* Add a verbose description to
``manila/api/openstack/rest_api_version_history.rst``. There should
be enough information that it could be used by the docs team for
release notes.
* Update the expected versions in affected tests.
Allocating a microversion
-------------------------
If you are adding a patch which adds a new microversion, it is
necessary to allocate the next microversion number. Except under
extremely unusual circumstances and this would have been mentioned in
the blueprint for the change, the minor number of ``_MAX_API_VERSION``
will be incremented. This will also be the new microversion number for
the API change.
It is possible that multiple microversion patches would be proposed in
parallel and the microversions would conflict between patches. This
will cause a merge conflict. We don't reserve a microversion for each
patch in advance as we don't know the final merge order. Developers
may need over time to rebase their patch calculating a new version
number as above based on the updated value of ``_MAX_API_VERSION``.
Testing Microversioned API Methods
----------------------------------
Testing a microversioned API method is very similar to a normal controller
method test, you just need to add the ``X-OpenStack-Manila-API-Version``
header, for example::
req = fakes.HTTPRequest.blank('/testable/url/endpoint')
req.headers = {'X-OpenStack-Manila-API-Version': '2.2'}
req.api_version_request = api_version.APIVersionRequest('2.6')
controller = controller.TestableController()
res = controller.index(req)
... assertions about the response ...