We had an extended discussion around this in the last community sync. Thanks for those who participated!
To sum up the discussion: --> As mesos devs, we should strive to not make incompatible changes in APIs, flags, environment variables. --> In the rare case where an incompatible change is preferred (e.g., code complexity), we should give a clear 6 months heads up the users that a breaking change is going to take place. --> Breaking changes do not necessitate a major version bump. This is because we want to allow live upgrades between major versions (e.g., 1.10 to 2.0). --> Compatibility guarantees do not apply to experimental features (incl. APIs). --> We need to have clear documentation about procedure that devs could follow when deprecating/removing stable features and adding experimental features. --> We need to improve upgrades.md to make it easy for operators to know what features are deprecated/removed between versions X and Y. --> We should decouple internal protos used by Mesos from the unversioned protos used by driver based frameworks. I will spend some time in the next few weeks to create/update the documentation reflecting these points. Anything else I missed? Thanks, On Sat, Oct 15, 2016 at 11:47 AM, haosdent <haosd...@gmail.com> wrote: > Thanks @yan's great inputs! I couldn't agree more almost of them. > > > Also the API is not just what the machine reads but all the documentation > associated with it, right? It depends on what the documentation says; what > the user _should_ expect. > > I think different users may have different expectations. And the guy who > developed the APIs may have different understand from some users as well. > Our documentations should cover most of cases. > > But in case that we didn't or forgot to write it explicitly in the > document, should we give up to update the API? Just like user Alice said > this is a BUG while user Bob said this is a feature. I think we still need > to raise it case by case to ensure most users are not affected by the > breaking API changes. > > On Sat, Oct 15, 2016 at 6:55 AM, Vinod Kone <vinodk...@apache.org> wrote: > > > We will chat about this in the upcoming community sync (thursday 3 PM). > > So, please make sure to attend if you are interested. > > > > On Fri, Oct 14, 2016 at 3:44 PM, Yan Xu <xuj...@apple.com> wrote: > > > >> > >> On Fri, Oct 14, 2016 at 3:37 PM, Yan Xu <xuj...@apple.com> wrote: > >> > >>> Thanks Alex for starting this! > >>> > >>> In addition to comments below, I think it'll be helpful to keep the > >>> existing versioning doc concise and user-friendly while having a > dedicated > >>> doc for the "implementation details" where precise requirements and > >>> procedures go. Maybe some duplication/cross-referencing is needed but > Mesos > >>> developers will find the latter much more helpful while the > users/framework > >>> developer will find the former easy to read. > >>> > >>> e.g., a similar split: > >>> https://github.com/kubernetes/kubernetes/blob/master/docs/api.md > >>> https://github.com/kubernetes/kubernetes/blob/master/docs/de > >>> vel/api_changes.md (which has a lot of details on how the kubernetes > >>> community is thinking about similar issues, which we can learn from) > >>> > >>> Jiang Yan Xu > >>> > >>> On Wed, Oct 12, 2016 at 9:34 AM, Alex Rukletsov <a...@mesosphere.com> > >>> wrote: > >>> > >>>> Folks, > >>>> > >>>> There have been a bunch of online [1, 2] and offline discussions about > >>>> our > >>>> deprecation and versioning policy. I found that people—including > >>>> myself—read the versioning doc [3] differently; moreover some aspects > >>>> are > >>>> not captured there. I would like to start a discussion around this > >>>> topic by > >>>> sharing my confusions and suggestions. This will hopefully help us > stay > >>>> on > >>>> the same page and have similar expectations. The second goal is to > >>>> eliminate ambiguities from the versioning doc (thanks Vinod for > >>>> volunteering to update it). > >>>> > >>> > >>> +1 Let me know if there are things I can help with. > >>> > >>> > >>>> > >>>> 1. API vs. semantic changes. > >>>> Current versioning guide treat features (e.g. flags, metrics, > endpoints) > >>>> and API differently: incompatible changes for the former are allowed > >>>> after > >>>> 6 month deprecation cycle, while for the latter they require bumping a > >>>> major version. I suggest we consolidate these policies. > >>>> > >>> > >>> I feel that the distinction is not API vs. semantic changes, Backwards > >>> compatible API guarantee should imply backwards compatible semantics > (of > >>> the API). > >>> i.e., if a change in API doesn't cause the message to be dropped to the > >>> floor but leads to behavior change that causes problems in the system, > it > >>> still breaks compatibility. > >>> > >>> IMO the distinction is more between: > >>> - Compatibility between components that are impossible/very unpleasant > >>> to upgrade in lockstep - high priority for compatibility guarantee. > >>> - Compatibility between components that are generally bundled (modules) > >>> or things that usually aren't built into automated tooling (e.g., the > >>> /state endpoint) - more relaxed for now but we should explicitly > exclude > >>> them from the guarantee. > >>> > >>> > >>>> > >>>> We should also define and clearly explain what changes require bumping > >>>> the > >>>> major version. I have no strong opinion here and would love to hear > what > >>>> people think. The original motivation for maintaining backwards > >>>> compatibility is to make sure vN schedulers can correctly work with vN > >>>> API > >>>> without being updated. But what about semantic changes that do not > touch > >>>> the API? For example, what if we decide to send less task health > >>>> updates to > >>>> schedulers based on some health policy? It influences the flow of task > >>>> status updates, should such change be considered compatible? Taking it > >>>> to > >>>> an extreme, we may not even be able to fix some bugs because someone > may > >>>> already rely on this behaviour! > >>>> > >>> > >>> API changes should warrant a major version bump. Also the API is not > >>> just what the machine reads but all the documentation associated with > it, > >>> right? It depends on what the documentation says; what the user > _should_ > >>> expect. > >>> > >>> That said, I feel that these things are hard to be talked about in the > >>> abstract. Even with a guideline, we still need to make case-by-case > >>> decisions. (e.g., has the documentation precisely defined this precise > >>> behavior? If not, is it reasonable for the users to expect some > behavior > >>> because it's common sense? How bad is it if some behavior just changes > a > >>> tiny bit?) Therefore we need to make sure the process for API changes > are > >>> more rigorously defined. > >>> > >>> Whether something is a bug depends on whether the API does what it says > >>> it'll do. The line may sometimes be blurry but in general I don't feel > it's > >>> a problem. If someone is relying on the behavior that is a bug, we > should > >>> still help them fix it but the bug shouldn't count as "our guarantee". > >>> > >>> > >>>> > >>>> Another tightly related thing we should explicitly call out is > >>>> upgradability and rollback capabilities inside a major release. > >>>> Committing > >>>> to this may significantly limit what we can change within a major > >>>> release; > >>>> on the other side it will give users more time and a better experience > >>>> about using and maintaining Mesos clusters. > >>>> > >>> > >>> According to the versioning doc upgradability depends on whether you > >>> depend on deprecated/removed features. > >>> > >>> That paragraph should be explained more precisely: > >>> - "deprecated" means your system won't break but warnings are shown > >>> (Maybe we should use some standard deprecation warning keywords so the > >>> operator can monitor the log for such warnings! > >>> - "removed": means it may break. > >>> > >>> If you deprecate a flag/env that interface with operator tooling in the > >>> next minor release, the operator basically has 6 months from the next > minor > >>> release to change the her tooling. I feel this is pretty acceptable. > >>> If you deprecate a flag/env variable that interface with the framework > >>> (executor) in the next minor release, I feel it may not be enough and > it > >>> probably warrants a major version bump. So perhaps the API shouldn't be > >>> just the protos. > >>> > >>> > >>>> 2. Versioned vs. unversioned protobufs. > >>>> Currently we have v1 and unnamed protobufs, which simultaneously mean > >>>> v0, > >>>> v2, and internal. I am sometimes confused about what is the right way > to > >>>> update or introduce a field or message there, do people feel the same? > >>>> How > >>>> about splitting the unnamed version into explicit v0, v2, and > internal? > >>>> > >>> > >>> As haosdent mentioned, we have captured this in MESOS-6268. The benefit > >>> is clear but I guess the people will be more motivated when we find > some v2 > >>> feature can't be made compatible with the v0 API. (Anand's point > >>> in MESOS-6016). On the other hand, if we cut v0 API access before that > >>> happens (is v0 API obsolete and should be removed 6 months after 1.0?) > then > >>> we don't need to worry about v0 and can use unversioned protos as > >>> "internal"? > >>> > >>> > >>>> Food for thought. It would be great if we can only maintain "diffs" to > >>>> the > >>>> internal protobufs in the code, instead of duplicating them > altogether. > >>>> > >>>> 3. API and feature labelling. > >>>> I suggest to introduce explicit labels for API and features, to ensure > >>>> users have the right assumptions about the their lifetime while > >>>> engineers > >>>> have the ability to change a wip feature in an non-compatible way. I > >>>> propose the following: > >>>> API: stable, non-stable, pure (not used by Mesos components) > >>>> Feature: experimental, normal. > >>>> > >>> > >>> +1 on formalizing the terminologies. > >>> > >>> Historically the distinction is not clear for the following: > >>> > >>> 1. The API has no compatibility guarantee at all. > >>> 2. The feature provided by this API is experimental > >>> > >> > >> To add to this point: because 2) logically doesn't apply to the "pure > >> (not used by Mesos components)" fields in the API, it could be more > >> confusing and thus require more precise definition. > >> > >> > >>> > >>> IMO It's OK that we say that we don't distinguish the two (the API has > >>> no compatibility guarantee until the feature is fully released) but we > have > >>> to make it clear. > >>> If we don't make such distinction, ALL API additions should be marked > as > >>> unstable first and be changed stable later (as a formal process). > >>> > >>> > >>>> > >>>> Looking forward to your thoughts and suggestions. > >>>> AlexR > >>>> > >>>> [1] https://www.mail-archive.com/user@mesos.apache.org/msg08025.html > >>>> [2] https://www.mail-archive.com/dev@mesos.apache.org/msg36621.html > >>>> [3] > >>>> https://github.com/apache/mesos/blob/b2beef37f6f85a8c75e9681 > >>>> 36caa7a1f292ba20e/docs/versioning.md > >>>> > >>> > >>> > >> > > > > > -- > Best Regards, > Haosdent Huang >
