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DefCore Committee Fall 2016 Interoperability Issues Report

Table of Contents

About This Document

OpenStack is tremendously flexible, feature-rich, powerful software that can be used to create clouds that fit a wide variety of use cases including software development, web services and e-commerce, network functions virtualization (NFV), video processing, and content delivery to name a few. Commercial offerings built on OpenStack are available as public clouds, installable software distributions, managed private clouds, appliances, and services. OpenStack can be deployed on thousands of combinations of underpinning storage, network, and compute hardware and software. Because of the incredible amount of flexibility OpenStack offers and the constraints of the many use cases it can address, interoperability between OpenStack clouds isn't always assured: due to various choices deployers make, different clouds may have some inconsistent behaviors.

One of the goals of the DefCore Committee's work is to create strong interoperability standards so that end users of clouds can expect certain behaviors to be consistent between different OpenStack Powered clouds and products. As the DefCore Committee has gone about its work of defining Interoperability Guidelines over the past few years, it has encountered various barriers to interoperability among OpenStack Powered clouds. The DefCore Committee seeks to work with the rest of the OpenStack Community to reduce or eliminate these barriers and recognize work that is being done to promote interoperability for end users of OpenStack Powered clouds.

To that end, the DefCore Committee has chosen to create a semi-annual report that highlights a few key interoperability challenges that the Committee has identified in the course of creating its Interoperability Guidelines. This report is not intended to be a comprehensive listing of all barriers to interoperability among OpenStack clouds--rather, it seeks to call out a small, actionable subset of those barriers to highlight their importance and request the community's focus toward discussing and resolving them. This report is also not intended to be critical of the work of OpenStack developers: its intent is to communicate feedback that the DefCore Committee has received constructively so that the issues are known to the Technical Committee and Project Teams and to enable discussion and improvement. The report also highlights known issues so that OpenStack deployers are aware of some choices they make when deploying OpenStack, and so that end users of OpenStack clouds are aware of some of the issues they may face when working with different OpenStack clouds.

The issues highlighted in this report are listed in no particular order, as their importance varies for different users and use cases. This report is intended to be periodically updated so that we can report on new issues that arise and progress being made on existing issues.

This report is not intended to prescribe or mandate solutions to interoperability problems. Often, the resolution to interoperability issues may involve changes to the OpenStack software, and while the DefCore Committee is generally happy to engage in creating solutions, technical governance is not the domain of the DefCore Committee or the Board of Directors. Rather, this report is intended to inform the Technical Committee and Project Teams about issues so that they can take action as they see fit.

Finally, the DefCore Committee would like to take this opportunity to thank the OpenStack community for its continued attention to interoperability issues. We congratulate OpenStack on its progress toward becoming "a ubiquitous Open Source Cloud Computing platform that is easy to use, simple to implement, interoperable between deployments, works well at all scales, and meets the needs of users and operators of both public and private clouds."

About The DefCore Committee

The OpenStack DefCore Committee was formed during the OpenStack Icehouse Summit in Hong Kong by a Board of Directors Resolution on November 4, 2013. DefCore sets base requirements by defining 1) capabilities, 2) code, and 3) must-pass tests for all OpenStack products. This definition uses community resources and involvement to drive interoperability by creating the minimum standards for products labeled "OpenStack." For more information about the DefCore Committee, please refer to the following resources:

You can communicate with the DefCore Committee via email at defcore-committee@lists.openstack.org, or on IRC in the #openstack-defcore channel on freednode.net.

Issue 1: Testing Interoperability

In order for OpenStack Powered clouds to prove that they behave consistently, the DefCore Committee requires that certain tests be successfully run against the cloud or product in question. These tests are listed in the DefCore Committee's Interoperability Guidelines. To date, all of the tests that the DefCore Committee has selected for its Guidelines are maintained by the OpenStack Community in Tempest1. Since no formal interoperability program existed prior to the DefCore Committee's creation, in some sense the decision to use Tempest tests as the basis of interoperability testing put Tempest tests in the position of being "used in a new way" compared to the use cases they were originally written for. The introduction of a new way to use Tempest has surfaced some design choices that were made that are better suited to the "traditional" uses for Tempest (such as CI testing at the development gates) than for interoperability testing.

One example of such an issue is implicit test requirements. For instance, a test might be written to test that Nova can boot an instance using the v2 API. In order to boot an instance, a user must first have an image stored in Glance to boot from. OpenStack provides several different ways to create a bootable image, not all of which may meet DefCore Criteria2 for inclusion in an interoperability Guideline. For example, the Glance v1 API may not be available to all users of some clouds since although v1 is "SUPPORTED", v2 is the "CURRENT" version of the Glance API.3 Some clouds may disallow uploading an image by policy and only allow users to use the Glance task API. If the test for booting an instance also attempts to create an image to boot using a method that doesn't meet DefCore Criteria, then passing the test effectively requires that a cloud support a Capability that the DefCore Committee did not intend to require.

As a second example, Interoperability Guidelines may cover releases that are commonly deployed and used in commercial products but are no longer tested in the upstream CI gate due to the branches having reached end-of-life in the development community. Because Tempest has traditionally focused its efforts on non-EOL branches, changes may be made to the tests that make them unusable with older releases. Since DefCore Criteria generally favor capabilities and APIs that are long-lived across multiple releases, this problem has not frequently manifested to date. However, there is potential for it to become more of an issue in the future.

As a third example, DefCore has chosen to only include tests in its Guidelines that can be repeated by end users of clouds in order to ensure that end users can verify whether or not a cloud they're considering using is in fact interoperable with others. This constraint means that tests that require administrator credentials are unsuitable for Interoperability Guidelines, since end users of clouds typically don't have administrative privileges. Some tests use administrative credentials for reasons of code efficiency (for instance, a base class might use administrative credentials because some tests that use it may genuinely need them, while others do not).

Because not all existing tests are suitable for inclusion in Interoperability Guidelines, the DefCore Committee has at times been unable to include a Capability in the Guidelines in spite of the Capability meeting the DefCore Criteria. As a result, users of OpenStack Powered clouds are unable to rely on those Capabilities to be present and functional.

The DefCore Committee recognizes that using existing tests for a new purpose may sometimes require tests to be refined or even for new tests to be written. In order for good interoperability tests to be developed, the DefCore Committee has created a specification that discusses what traits we look for in a test that is suitable for inclusion in the Interoperability Guidelines. It is our hope that this listing will help foster awareness and understanding within the development community as tests are created, updated, or moved into Tempest over time.

Issue 2: Varying Models for API Evolution

APIs are a very important contact point between the OpenStack software and end users: whether they're using one of OpenStack's own clients, a third party management tool, or an SDK developed outside of the OpenStack community, they all end up using OpenStack's APIs in some way.

OpenStack also has a very diverse community of projects under the Big Tent in various stages of development: some have been around since the beginning of OpenStack and have mature, fairly stable APIs. Others are new and evolving quickly and may iterate on their APIs faster. Some projects have moved to a microversioning model4, others haven't. Some projects that have gone through major-version API changes over time have elected to continue supporting older versions of their API for long periods, while others have chosen to deprecate and remove older versions of their API relatively quickly. At times, announced plans to make modifications to which APIs are CURRENT, SUPPORTED, and DEPRECATED have changed, and feedback we've received indicates that communication around API changes isn't always clear and consistent to parties outside of the OpenStack ecosystem (for example: developers of third party SDKs and tools that don't regularly read posts on the high-volume openstack-dev@lists.openstack.org mailing list and may not regularly attend project IRC meetings). API transitions for projects that depend on one another within OpenStack aren't always handled uniformly: sometimes one project continues to call an older version of another project's API for quite some time after a newer version is released5. Some "tribal knowledge" has also developed within OpenStack over time: for example, APIs that OpenStack developers themselves say should only be used internally by other OpenStack services and shouldn't be exposed to end users (documentation of which may be scant or non-existent).

OpenStack has and wishes to maintain a rich ecosystem of tools that consume OpenStack's services but are developed outside of OpenStack itself, and many users of OpenStack clouds depend on this ecosystem6 when developing applications for OpenStack clouds.

Differences in how OpenStack projects handle API transitions and in how transitions and plans are communicated to the outside world at times make it difficult to know when external tools need to be updated. For example, some external toolkits may be surprised when an API becomes deprecated quickly for one project after observing another project maintain older versions of an API indefinitely. They may rely on an API version being exposed to end users that many clouds don't actually expose. Updating external tools and clients requires real time and effort from their maintainers, so some may be reluctant to move to a newer API version unless it's very clear to them that there is added value in doing so or that they absolutely need to because the version they're currently using is being removed.

When APIs become inconsistently adopted either within OpenStack or among external tools, those inconsistencies are often reflected in certain capabilities failing to meet DefCore Criteria. For example, if many third party SDKs are split between supporting Glance v1 and Glance v2, those individual APIs may have trouble achieving the "Used by Tools" criteria. If OpenStack's own clients and other projects keep relying on an older API, the new API may be unable to achieve the "Used by Clients" and "Foundation" criteria. If APIs are iterated quickly between versions of OpenStack or only some clouds disable a particular version of an API from being consumed by end users, the API may be unable to achieve the "Widely Deployed" criteria. Failing to meet Criteria means that a capability can't be introduced into an Interoperability Guideline since it is not, in fact, interoperable.

Issue 3: External Network Connectivity

Networking is a complex topic by its very nature: different use cases or organizational constraints may demand different network models. OpenStack in turn provides a great deal of flexibility in networking, with several models available in Neutron. For many users of clouds, the ability to get a compute instance connected to the outside world is a particularly important capability. For example, a popular use case for OpenStack is "web services and e-commerce"7. E-commerce platforms generally feature some webserver instances that need publicly routable IP addresses so that customers can reach the site. Another popular use case is "Software dev/test/QA and CI", and many continuous integration systems need to pull packages and software updates from repositories outside of their own networks.

OpenStack provides many options for getting external connectivity to compute instances: in some cases, users create a private network and attach floating IP addresses to instances that need to be reachable from the Internet. In others, users must attach instances that they want to be reachable from the public Internet to a specific administratively-created provider network. In other cases, instances are booted onto a specific network that provides external reachability by default.

Unfortunately, the differing network models that OpenStack provides for also introduce some complexity for clients and app developers: the method they use to get external reachability differs from cloud to cloud. Discovering the correct method can be complicated, and is often done by reading documentation provided by the cloud administrator rather than programmatically. Once the user discerns the correct methods for each cloud they want to use, they are still often forced to complicate their code with if/else loops or similar constructs because of the varying models in use:

if cloud == 'Cloud A':
    # The IP address we were given at boot time is public; do nothing.
elif cloud == 'Cloud B':
    attach_floating_ip_to_instance(myinstance)
elif cloud == 'Cloud C':
    attach_instance_to_network('c8c43765-53cf-4030-a115-a89471ded2ed')

Because making an instance externally reachable is such a common need and because the networking models used by deployers differ so greatly, this is a particularly challenging issue for end users.

Issue 4: API and Policy Discoverability

OpenStack frequently offers more than one method to accomplish a given end-user objective. For example: a user wishing to create an image might call Nova's API to make an image of a currently running instance, or they might upload an image through the Glance v1 API, the Glance v2 API, or they might use an import task. All of these methods create an image, but all are different API calls. Generally speaking, the mechanics are very different and are intended to address different use cases. Sometimes the use cases are similar but the API calls are different (for example, using a similar API call to the v1 endpoint vs the v2 endpoint). Further, most OpenStack projects offer policy controls that can be configured by cloud administrators: for example, a cloud administrator might disable the Glance v1 API for end users or might only allow image creation via the task API (or indeed may not allow image creation at all, and instead restrict users of the cloud to images created by administrators). Further still, some capabilities may be exposed to some users of clouds (for example, project administrators) but not others (project members).

Discovering which capabilities and methods are available and accessible to end users can be a somewhat frustrating exercise that often amounts to trial and error:

def create_image(image, cloud)
    '''Create an image in a cloud.'''
    try:
        create_image_via_glance_v1_upload(image, cloud)
    except ApiNotAvailableError:
        try:
            create_image_via_glance_v2_upload(image, cloud)
        except UnauthorizedError:
            try:
                create_image_via_glance_import_task(image, cloud)
            except:
                print "I can't or don't know how to create an image in this cloud"

Some external tools and SDKs simply assume that certain capabilities are available to all users which causes frustration for users of clouds in which those capabilities are not available to them. The varying policy settings and API versions available among differing clouds coupled with the differing adoption of methods among clients may cause some Capabilities to not meet DefCore Criteria.

In most cases, the versions of an API that are available are discoverable via a GET request to the root URL of an API endpoint (though in some cases a client may also need to check microversion headers if the project is known to use microversions). In some cases there is no test coverage for the discovery API in Tempest8, which limits DefCore's ability to add tests for the discovery API to an Interoperability Guideline. Policy is often trickier to programmatically discover as policy files are only available to cloud administrators.

The issue of discoverability also impacts what tests can be included in Interoperability Guidelines in another way: some tests assume that particular methods of accomplishing an end-user objective are available, and rely on them to set up for the capability they actually want to test. Drawing on the example above, a test for the ability to boot an instance in Nova might need to create an image to boot, and might assume that Glance v1 is both supported by the cloud and available to the unprivileged user running the test. As per Issue 1 described previously in this document, if that method isn't actually interoperable, the test for booting an instance may be excluded from an Interoperability Guideline even if booting an instance is actually an interoperable capability. If the test instead had a way to discover how the cloud allowed the user to create images and implemented that method as part of its fixture, the test would likely be more suitable for inclusion.

Issue 5: Lack of Clarity on DefCore's Purpose and Abilities

Although the DefCore Committee was initially created almost three years ago, the program has taken some time to evolve its operating procedures and develop Guidelines. Some further time elapsed before Guidelines included enough required Capabilities to be genuinely useful as decision-making tools for many consumers of OpenStack clouds, vendors designing products or services built on OpenStack, prospective customers of those products and services, and the tooling ecosystem. Over that time, the role of the DefCore Committee has been a matter of many discussions within the community. For example, some feedback we've received indicates that there is some sentiment that the DefCore Committee can "bless" a capability by including it in an Interoperability Guideline based on whether or not the Committee members feel that all clouds should support the capability. In fact, most of the DefCore Criteria are trailing indicators of whether or not a capability has become widely adopted throughout the ecosystem. The DefCore Committee also does not mandate technical decisions for projects such as when an API should be deprecated, how or if a capability that has been deemed not interoperable must be improved or replaced, or how Tempest tests should be designed. Technical governance of OpenStack's development instead resides with the projects themselves and ultimately with the Technical Committee.

The logo programs9 that Interoperability Guidelines govern admission to are designed to be simple. They allow a product or service built on OpenStack to use a logo that indicates it is interoperable. The logo is a very easily recognizable mark that indicates some base level of interoperable functionality is available, and is thus easy for consumers of OpenStack clouds to look for. However, users must dig a bit further to really understand which Capabilities are actually interoperable. A list of Capabilities and required tests are published with each Guideline, but the tests may not easily map to particular APIs that users are interested in using. Users may also need to compare different Guidelines to determine differences in the Capabilities covered if they are concerned with clouds that have demonstrated compliance with different Guidelines. Even armed with a list of tests, users may require that some Capabilities not covered by the Guidelines be present in products that they choose to use--and there's currently no good way for them to determine which products support those Capabilities.

Concluding Remarks and Acknowledgements

The DefCore Committee hopes that this report is informative and useful in directing attention to current interoperability challenges. We believe that focussing attention on these issues will ultimately lead to a more interoperable ecosystem for OpenStack users. We believe that the OpenStack ecosystem strongly desires interoperability among clouds, and congratulate OpenStack on progress already being made toward fostering greater interoperability among OpenStack clouds. We look forward to sharing updates on these issues and more in future reports.

In particular, the DefCore Committee would like to gratefully acknowledge the feedback and engagement we've received from:

  • The OpenStack Foundation and its Board of Directors.
  • The Technical Committee.
  • The User Committee.
  • Providers of products and services built on OpenStack.
  • The RefStack project team.
  • PTLs and Project Teams who contributed to identifying interoperable Capabilities and working to improve the interoperability of their projects.
  • The OpenStack QA team for its assistance in refining tests and working with the DefCore Committee to expand and maintain interoperability tests.
  • End users of OpenStack who've provided feedback and frank conversation.

Without the participation of such a broad swath of our community, this report and indeed most of the DefCore Committee's work would not be possible. Thank you for your support.

If you wish to provide feedback or engage the DefCore Committee in other ways, please contact us at defcore-committee@lists.openstack.org.

  1. Notably, in 2016 the Technical Committee passed a resolution indicating its preference that the DefCore Committee use tests in the Tempest source tree for its Guidelines.↩︎

  2. Refer to the Core Criteria document for more details.↩︎

  3. As of this writing. Refer to the OpenStack API Complete Reference for more information.↩︎

  4. For example, refer to Nova's Microversions documentation.↩︎

  5. As an example, the Glance v1 API was moved from CURRENT to SUPPORTED status in the spring of 2015 in the Kilo release. Nova will continue to depend on the v1 API until the Newton release in the fall of 2016. Refer to the Nova Add support for Glance v2 API Spec for more information.↩︎

  6. Refer to page 22 of the April 2016 User Survey for examples, a few of which include libcloud, FOG, jclouds, Terraform, and clients that users wrote themselves.↩︎

  7. Refer to page 35 of the April 2016 User Survey.↩︎

  8. As an example, Neutron did not have a Tempest test for the "list API versions" API until one was created in June 2016 after the gap was identified during capabilities scoring activities for the 2016.08 Interoperability Guideline.↩︎

  9. Refer to: http://www.openstack.org/brand/interop/↩︎