The trick lies in how strict your serialization/deserialization is. If you only lock to the ATC Major rev, routine development can break strict marshalling code as new fields are added/removed or methods are added/removed in our primary master branch. Suppose you're using the golang or python native client libraries off the head of master, even if you're vendoring the library properly the REST calls you're making may give different answers (possibly even breaking the deserializer code) or reference non-existent routes. This is where the conversation about SemVer comes in. A lot of API and library development projects have adopted this model because it solves this exact problem. Another possible solution is that 3rd parties simply never adopt the current ATC major API version and rely on the stable API promise of the deprecated api version. The downside is that you won't be able to use any new functionality and you won't have a transition window since the promise is only Current Release+1 instead of Current Release+2.
Regarding discoverability (#6) of available API versions there is already an issue open for that: https://github.com/apache/trafficcontrol/issues/2872 Jonathan G On 3/13/19, 9:15 AM, "Hank Beatty" <hbea...@apache.org> wrote: Hello Rawlin, Wow! I know that you are obviously really passionate about this because that was a really long email. :) Here are my thoughts on API versioning: 1. The URL for the API should follow the TC major version (e.g. http://.../api/v3/...) 2. TC 3.x.x would support v2 (with a warning message that it is obsolete) and v3 of the API. 3. TC 4.x.x would support v3 (with a warning message that it is obsolete) and v4 of the API. 4. A user of the API should not have to call v1.2, v1.3, and v1.4 in the same script. This would be taken care of with 1, 2, and 3 above. 5. In the documentation, define "backward compatible" as new fields will be introduced within a major version but, will always be optional for both GET and POST. 6. If a user really wants to know the specific version (x.x.x) of the API there should be an API route (e.g. https://.../api/v3/version). Yes, I know that #2 is not how it is today. Traffic Control does not do enough minor and bug fix releases that this should cause that big of an impact. Regards, Hank On 3/11/19 5:55 PM, Rawlin Peters wrote: > Hey Hank, > > I don't think we are planning on releasing TO separately from the rest > of TC, nor do I think we should. The TO API version should not be the > same as the overarching TC version, because that would make it unclear > whether or not an old script/client/whatever is expected to continue > to function properly with a new version of TC. > > The TO API version should provide some level of confidence that > scripts/clients/etc that have been coded against a particular API > major version will always work against that particular API major > version. Historically, we have inadvertently broken this "promise" due > to making backwards-incompatible changes to the 1.x API, but I believe > we are getting better at avoiding those breaking changes where its > reasonable. > > For example, let's say you were working with TC 3.0 and wrote a script > against TO API V1 that GETs a bunch of servers, makes some changes, > then PUTs those changes back. Then you upgrade to TC 4.0 later. Should > your script continue to work as-is? As long as V1 of the API is still > supported in TC 4.0, you should have some level of confidence that > your script will still work with TC 4.0. > > If the TO API was left un-versioned, every time you upgrade TC you > will have no real idea whether or not your old script is still going > to work. Some day, the script _won't_ work due to > backwards-incompatible changes made to the API. However, in a > major-versioned world, this would be in API V2, and your script would > stop working once API V1 is no longer supported, which hopefully would > not be a surprise since we'd have to follow a schedule like this: > > - TC 3.0 released (supports TO API v1) > - TC 4.0 released 6 months later (supports TO API v1 _and_ v2, but v1 > is now "obsolete") > At this point, you should convert any scripts/clients/whatever that > have been written against API v1 to work against the new API v2. > - TC 5.0 released 6 months later (now only supports TO API v2 -- > requests made to the v1 API will fail immediately saying the v1 API is > no longer supported) > At this point, you should not upgrade TO to 5.0 until you are > reasonably confident that you've gotten all your old v1 > scripts/clients/etc to work against TO API v2, which you've had 6 > months notice to complete already. > > If we left the TO API un-versioned or simply matched it to the TC > version, I think we'd fall into the trap of constantly making breaking > API changes with no notice, which is bad for anything that uses the > API. It would make upgrading major TC versions a nightmare since you'd > never really know if some script/client/etc was going to break after > the upgrade is completed. Using a major-versioned approach for the TO > API will make the upgrade process much smoother in the long run and > allow us to introduce breaking-API improvements without completely > blindsiding users. > > This approach would also help in-repo clients like Traffic Portal. > Today, Traffic Portal seems to be pretty much all-in on a single API > version. When we implement a TO API v2, we wouldn't immediately also > have to go fix Traffic Portal to work with the TO API v2 version. This > means we can work on the API and UI separately, leading to more > focuses PRs and therefore a quicker PR review process, which is better > for contributors and reviewers. > > On a related note, the TO API major version doesn't have to be an "all > or nothing" kind of thing, so we shouldn't make our clients be > "all-in" on a single API major version. That is, we shouldn't have a > single global constant in the client that controls the API version it > requests across all endpoints. I imagine we will introduce v2 > endpoints on an endpoint-by-endpoint basis, deprecating v1 endpoints > as we go, so clients should be designed to support this kind of mixed > versioning eventually. > > - Rawlin > > On Mon, Mar 11, 2019 at 1:17 PM Hank Beatty <hbea...@apache.org> wrote: >> >> Hello Rawlin, >> >> What is your reasoning to keep the API version separate from the TC version? >> >> The only reason that I can think of is that the Traffic Control Project >> team would plan on releasing an API (TO) version separately from the >> rest of the components. Is this something that we are planning on doing >> in the future? From what I know we have not done that up to this point. >> >> Regards, >> Hank >> >> On 2/14/19 12:53 PM, Rawlin Peters wrote: >>> There is a lot of stuff to digest here, and I agree that the v1 API is >>> desperately in need of a good v2. However, I'm not sure I agree that >>> the API should be versioned alongside Traffic Ops. The API version >>> should be separate from the Traffic Ops/Traffic Control release >>> versions. We should do our best to not break a major API version, so >>> in theory a script written against TO API v1 should always work with >>> TO API v1. When TO API v2 is introduced, the script written against v1 >>> would not be guaranteed to work against v2 (although, we should still >>> support v1 for some time before deprecating in favor of v2). >>> >>> - Rawlin >>> >>> On Thu, Feb 14, 2019 at 8:07 AM Fieck, Brennan >>> <brennan_fi...@comcast.com> wrote: >>>> >>>> I'd take it further, though in my opinion it shouldn't be done until we're ready to do away with Perl entirely. >>>> I've been working on this for a little bit, and I sorta wanted to make a wiki page for a proposed API v2 design before sending it, but what the heck. The conversation is here now. >>>> >>>> >>>> I don't like the way our API is versioned. Let me be clear, it _should_ be versioned, and the >>>> versions _should_ be semantic, but it is my opinion that the API should be versioned alongside >>>> Traffic Ops rather than at its own pace. I've written essentially an article on why this should be >>>> the case, and it follows: >>>> >>>> ** TIMING ** >>>> The first issue I should address is timing - this needn't happen immediately. For the time being, I >>>> think a radical change would be much more harmful than continuing along our current versioning >>>> scheme. This change should be implemented with the advent of what we currently refer to as "API v2". >>>> Presumably, at this time all of the Perl code has been removed and we are looking to re-tool the API >>>> to be more sensible and standards-conforming. It's a time when we'll already be making big, breaking >>>> changes. I personally would love for this to be ATC 4.0, but that may not be a realistic goal. >>>> >>>> ** REDUNDANCY ** >>>> The easiest to see - albiet simultaneously most trivial - issue with the current API versioning >>>> scheme is how every request path must start with '/api/1.x/'. This is annoying, to be frank; >>>> especially when one considers that the current plan for Traffic Ops is to reduce it entirely to an >>>> API, so literally every endpoint will have '/api/' in common. We _know_ the endpoint we are trying >>>> to query is an API endpoint because _all_ endpoints are API endpoints. When we reach "API v2" the >>>> '/api/' part of request paths will have lost all value entirely. >>>> Even with that gone we are left with '/1.' (or '/2.' as the case may become) as a common prefix, >>>> again annoying although not totally useless in this case. However, the vast majority of API >>>> endpoints see no changes between minor versions, so really '/1.x' just becomes a static, constant >>>> prefix where 'x' is the latest version of the API. >>>> In any case, versioning the API alongside Traffic Ops solves this problem because our Traffic Ops >>>> server(s) emit HTTP headers that name the server. Once Perl is gone, we'll be free to use the HTTP >>>> `Server:` header to name the server e.g. `Server: Traffic Ops/3.2.1`. At this point, we could >>>> either implement an `OPTIONS` method request at the server's root that would just return some >>>> headers - including `Server:` or just let people to a `GET` (or better yet `HEAD`) request to >>>> `/ping` and pull the server version out of the headers. The client then has all the information it >>>> needs to communicate effectively with the server. The alternative to this within our current >>>> versioning schema is to implement an unversioned API endpoint such that we have a hundred `/api/1.x` >>>> endpoints and one that has some other - or possibly no - prefix, or have a versioned API version API >>>> endpoint, which is confusing even just to say. >>>> >>>> ** TRAFFIC OPS _IS_ THE API ** >>>> As mentioned previously, the endgame of our transition from Perl to Go is that Traffic Portal is the >>>> only UI for ATC - and in fact that's already somewhat true. That leaves Traffic Ops as a database >>>> and a REST API for interacting with said database. In fact, the database is often referred to as its >>>> own service: "ToDb", "Traffic Ops DB" etc. That means that we have the single most important Traffic >>>> Control component split in two - half of its functionality is versioned sanely with Traffic Control >>>> while the other half is versioned separately from anything else in the world. That's crazy, because >>>> if you have a program that only does two things, then surely a breaking change to one of those >>>> things means increasing its major version? If that's the case, then why are we not versioning the >>>> API alongside Traffic Ops? >>>> It may be argued (incorrectly, in my opinion) that Traffic Ops does more than serve an API to >>>> interact with a database. It generates configuration files and system images, it combines data and >>>> does heavy processing on it. But really those things shouldn't be taken into account in a versioning >>>> scheme except insofar as they affect the experience of some user, administrator, or application >>>> interfacing with Traffic Ops. If the API responses don't change in form or content, and if the >>>> process of setting up or maintaining the application haven't changed, then any code changes you've >>>> made are a patch, not a version change. Traffic Ops does big things, but at the end of the day it >>>> all just boils down to API inputs and outputs as far as anything and anyone else is concerned. >>>> >>>> ** CONFUSION ** >>>> We currently live in a world where I can run a script using the Traffic Ops API that works perfectly >>>> fine against Traffic Ops version 3.2.1, but then if I again test it against version 3.2.1 at some >>>> point in the future it breaks because breaking changes were made in the API. It's easy to say, "oh, >>>> that just means that when we make breaking API changes we should increment the version >>>> appropriately," but realize that this _is versioning the API alongside Traffic Ops_. If we're not >>>> doing that, we're saying there is unpredictability with the behavior of our system within releases, >>>> and if we _are_ doing that then the only difference between the API version and the Traffic Ops >>>> version is that the API version is confusingly behind by about 2 major revisions. It should just be >>>> the same for simplicity's sake. >>>> >>>> ** THE API "PROMISE" ** >>>> The single most common argument I hear in favor of our current API versioning scheme is "well we've >>>> said an API version 1.x behaves in this way, and so we must uphold that promise to the user base". >>>> Not only do we routinely break that promise already, >>>> (e.g. PR #3110 [https://github.com/apache/trafficcontrol/pull/3110]) but I'm certainly not >>>> suggesting that we don't uphold this promise. Yes, this does mean that making breaking API changes >>>> in TO would require a new major release and adding features/fields to the API would require a new >>>> minor release. I don't see that as a big deal, especially if implemented at the time I'm suggesting >>>> when we'd be re-designing the API - and it does sorely need to be redesigned. >>>> >>>> * The API Needs to be Redesigned * >>>> I'm going to go down this rabbit hole for a second, if you're already convinced the TO API needs a >>>> re-design then feel free to skip this section. I'm not going to touch on any problems caused in the >>>> API as currently implemented by the use of a standalone API version - that's what the entire article >>>> is for. >>>> Currently, our API currently has three huge problems: >>>> >>>> 1. Rampant oversaturation of endpoints >>>> We have a systemic issue of re-implementing behaviour in multiple endpoints. This is due in part >>>> to a lack of good documentation - so developers aren't aware of the endpoints available to them >>>> - and partly because of the "Mojolicious Mindset" that plagues our oldest endpoints. The >>>> "Mojolicious Mindset" refers to the use of URL path fragments as request parameters, e.g. >>>> '/users/{{ID}}' instead of/in addition to '/users?id={{ID}}'. From the perspective of someone >>>> who is just writing the back-end for these endpoints, there's no clear advantage to one over the >>>> other except that the former seems to more clearly reflect the intent of requesting a specific >>>> object whereas the latter could be seen as more of a "filter" on a larger collection. That's not >>>> incorrect, necessarily, but the two are totally separate request paths, so having '/users' and >>>> '/users/{{ID}}' means documenting two endpoints instead of one, and it means two lines in the >>>> route definitions, and it means two seperate handlers instead of one (albiet a more complex >>>> one). >>>> Consider also that we have all of the following endpoints for manipulating Cache Groups: >>>> >>>> * /api/1.x/cachegroup/{{parameter ID}}/parameter >>>> * /api/1.x/cachegroup_fallbacks >>>> * /api/1.x/cachegroupparameters >>>> * /api/1.x/cachegroupparameters/{{ID}}/{{parameter ID}} >>>> * /api/1.x/cachegroups >>>> * /api/1.x/cachegroups/{{ID}} >>>> * /api/1.x/cachegroups/{{ID}}/deliveryservices >>>> * /api/1.x/cachegroups/{{ID}}/parameters >>>> * /api/1.x/cachegroups/{{ID}}/queue_updates >>>> * /api/1.x/cachegroups/{{ID}}/unassigned_parameters >>>> * /api/1.x/cachegroups/{{parameter ID}}/parameter_available >>>> * /api/1.x/cachegroups_trimmed >>>> >>>> These could all be collapsed neatly into one or two endpoints, but were instead implemented >>>> separately for whatever reason(s) >>>> (see Issue #2934 [https://github.com/apache/trafficcontrol/issues/2934] for details). >>>> >>>> 2. Improper/Non-existent standards conformity >>>> We have requests that should be read-only that make server-side state changes (Issue #3054 >>>> [https://github.com/apache/trafficcontrol/issues/3054]), we have endpoints returning success >>>> responses on failure (Issue #3003 [https://github.com/apache/trafficcontrol/issues/3003]) and >>>> our "CRUDER" has failed us. `PUT` should be used to _create_ objects (or possibly update them by >>>> creating an alternative representation with the same identifiying information) but is instead >>>> used as the primary "edit this" method. `POST` is for processing entities in a data payload, but >>>> is instead used for object creation. `PATCH` languishes, totally unimplemented. These problems >>>> are systemic and stem partially from the "Mojolicious Mindset" whereby new functionality is >>>> introduced into the API by first considering what request method is appropriate and then >>>> deciding on a request path that names the operation being done. Request methods are meant to be >>>> the different ways in which a client interacts with a resource on the server, and thus the >>>> resources themselves should be considered primary. The "CRUDER" hampers this mindset, because it >>>> makes treating payloads and query parameters generic and isn't receptive to injection of new >>>> behaviour. >>>> The "CRUDER" is a great innovation, to be sure, as it saves us quite a bit of time and prevents >>>> duplicating code, but the problem it solves is an emergent property of of API problem #1 above. >>>> With fewer endpoints we'd have much more specific handling, and the need for and advantages of >>>> the "CRUDER" will vanish. >>>> >>>> 3. Needing multiple queries to obtain a single piece of information >>>> This issue is pretty deeply rooted, and is related to the way our database is structured. But >>>> that's part of the problem - an API needn't replicate the database, and is therefore free from >>>> some of the constraints that bind a database. >>>> The way things are now, in order to e.g. create a server definition I must make several >>>> preliminary requests to determine the integral, unique, non-deterministic identifiers of other >>>> objects. I think we all agree that ideally these integral IDs would have no part in the output >>>> of the API, and many people I've spoken to would support wiping them from the database entirely >>>> given enough time and manpower. >>>> >>>> ________________________________________ >>>> From: Robert Butts <r...@apache.org> >>>> Sent: Wednesday, February 13, 2019 6:11 PM >>>> To: dev@trafficcontrol.apache.org >>>> Subject: Re: [EXTERNAL] Re: Traffic Ops API versioning issues >>>> >>>>> It doesn't seem like the idea of full TO API SemVer was ever fully >>>> discussed and voted on >>>> >>>>> Since it seems like we never truly committed to SemVer with minor versions >>>> for the TO API >>>> >>>> There was consensus: >>>> https://lists.apache.org/thread.html/8f8a850c68424021a0fe06967894383a24e463f1b0cee4d652d04590@%3Cdev.trafficcontrol.apache.org%3E >>>> https://lists.apache.org/thread.html/1a42a2192a81fc4d76639ccd10761b6b73c31345a63715bb8aa86e4e@%3Cdev.trafficcontrol.apache.org%3E >>>> >>>> We didn't do an official [VOTE], but we rarely do that as a project, unless >>>> there's difficulty reaching unofficial consensus. That said, there's >>>> nothing stopping another discussion or vote, if we want to change things. >>>> >>>>> as long as we set the expectations for the user >>>> >>>> That's precisely my point. We can always say "we set the expectations, it's >>>> the user's fault for misreading, or misunderstanding, or not noticing a >>>> changelog." It's not about fault, it's about providing a better user >>>> experience. >>>> >>>>> that support has to be baked into traffic_ops_golang such that it's easy >>>> and maintainable to support tons of minor versions. If we keep heading down >>>> our current path we are going to be left with a giant mess. >>>> >>>> I don't think anyone disagrees. Traffic Ops versioning has had considerable >>>> technical debt for some time now. We just haven't been willing to spend the >>>> time to fix it. I agree, that needs to change. >>>> >>>> I'd also like to note, there's another option: code generation. We can keep >>>> the structs and handlers largely the same, and generate the "duplicate" >>>> code when a new minor version is added. There's a strong argument that this >>>> is the "idomatic" way to solve this problem, for the Go language. I >>>> personally feel Reflection is better here. But, I wanted everyone to be >>>> aware that's an option, if the consensus is that it's the best option. In a >>>> nutshell, we could generate code with a script (with a spectrum of >>>> precision and complexity, from `cp && sed` to parsing the AST), and >>>> `routes.go` would have a `//go:generate` header. For examples, see: >>>> >>>> https://blog.golang.org/generate >>>> https://godoc.org/golang.org/x/tools/cmd/stringer >>>> >>>> I did some prototyping of that approach, if anyone is interested, just let >>>> me know and I can provide examples of what that would look like. >>>> >>>> >>>> On Wed, Feb 13, 2019 at 5:09 PM Rawlin Peters <rawlin.pet...@gmail.com> >>>> wrote: >>>> >>>>> On Wed, Feb 13, 2019 at 1:20 PM Gray, Jonathan >>>>> <jonathan_g...@comcast.com> wrote: >>>>>> >>>>>> I'm +1 on keeping full API SemVer. >>>>> >>>>>> On 2/13/19, 12:16 PM, "Robert Butts" <r...@apache.org> wrote: >>>>>> >>>>>> We would be abandoning Semantic Versioning. >>>>> >>>>> This is why I wanted to open this up for broader discussion within the >>>>> community. It doesn't seem like the idea of full TO API SemVer was >>>>> ever fully discussed and voted on (at least not to my knowledge), >>>>> which is why I haven't been abiding by it myself or enforcing it upon >>>>> other TO API devs either. If we're going to truly commit to SemVer >>>>> with minor versions for TO API then we should fully understand the >>>>> cost vs utility of doing so. Also, SemVer doesn't have to be an "all >>>>> or nothing" thing, as we currently choose to ignore the "patch" >>>>> version for the TO API. We could also choose to ignore the minor >>>>> version and just focus on the most important aspect of SemVer which is >>>>> not introducing backwards-incompatible changes in the same major >>>>> version. >>>>> >>>>> Since it seems like we never truly committed to SemVer with minor >>>>> versions for the TO API, traffic_ops_golang wasn't designed to easily >>>>> support minor versions. So if we're going to truly commit to SemVer >>>>> with minor versions for TO API, then that support has to be baked into >>>>> traffic_ops_golang such that it's easy and maintainable to support >>>>> tons of minor versions. If we keep heading down our current path we >>>>> are going to be left with a giant mess. >>>>> >>>>> The only way I can get behind supporting the "minor version promise" >>>>> is if we have a way to basically just tag fields as introduced in a >>>>> specific API version, with just a single struct per resource and a >>>>> single handler per major version of an endpoint. We should only >>>>> require a single implementation of an endpoint per major version. If a >>>>> custom JSON parser allows us to do that, then that's great. Without >>>>> that, I don't think supporting the "minor version promise" is even a >>>>> viable option. >>>>> >>>>> A lot of those scenarios around user confusion due to supporting just >>>>> a major version are not really an issue as long as we set the >>>>> expectations for the user. I.e.: >>>>> - clients should request v1 >>>>> - as the v1 API is enhanced in a backwards-compatible manner, clients >>>>> will begin to see new fields in the server responses >>>>> - if a client wants to modify a resource, they will typically do a GET >>>>> on the resource, modify the resource, then do a PUT back to the >>>>> server. >>>>> - in the GET response, if the client sees new fields, they can expect >>>>> to modify those fields and see it reflected on the server. >>>>> - if the client does NOT see new fields, then they cannot add fields >>>>> and expect to see that reflected on the server >>>>> - null values in optional fields will be interpreted by the server as >>>>> whatever the default for that optional field is. So if the default for >>>>> new optional field "foo" is 5, then a client sending `"foo": null` >>>>> will be interpreted by the server as `"foo": 5`, and `"foo": null` >>>>> should never have a different meaning than `"foo": 5` on the server. >>>>> >>>>> The advantage of just supporting the "major version promise": >>>>> - jives better with Go's lack of metaprogramming >>>>> - no custom JSON parser in Go required >>>>> - less general overhead in development >>>>> - only have to worry about breaking changes >>>>> - no worrying about which fields belong to which minor versions >>>>> - no extra API testing to make sure fields introduced in API v1.N >>>>> aren't returned to v1.N-1 clients >>>>> - don't have to update every single client in the repo with the new >>>>> minor version every time a minor version is incremented (since clients >>>>> would just specify the major version) >>>>> >>>>> So, as a community, we need to weigh these options and decide whether >>>>> or not we want to take the "major version only" route or the "major >>>>> plus minor version" route. Personally, I prefer the "major version >>>>> only" route because it means less code, less overhead, less >>>>> coordination, and less things to potentially go wrong. However, if a >>>>> relatively small custom JSON parser is all we really need to >>>>> reasonably support the "minor version promise", then I can't say I'm >>>>> completely against that route either (just that I wouldn't prefer it). >>>>> >>>>> - Rawlin >>>>>
