3 title: "VPP API Flag Day Algorithms"
6 # VPP API Flag Day Algorithm
10 This document describes the current solution to the problem of
11 automating the detection of VPP API changes which are not backwards
12 compatible with existing CSIT tests, by defining the "Flag Day"
13 process of deploying a new set of CSIT tests which are compatible
14 with the new version of the VPP API without causing a halt to the
15 normal VPP/CSIT operational CI process. This is initially
16 limited to changes in \*.api files contained in the vpp repo.
17 Eventually the detection algorithm could be extended to include
18 other integration points such as "directory" structure of stats
19 segment or PAPI python library dependencies.
23 Aside of per-release activities (release report), CSIT also provides testing
24 that requires somewhat tight coupling to the latest (merged but not released)
25 VPP code. Currently, HEAD of one project is run against somewhat older codebase
26 of the other project. Definition of what is the older codebase to use
27 is maintained by CSIT project. For older CSIT codebase, there are so-called
28 "oper" branches. For older VPP codebase, CSIT master HEAD contains identifiers
29 for "stable" VPP builds. Such older codebases are also used for verify jobs,
30 where HEAD of the other project is replaced by the commit under review.
32 One particular type of jobs useful for VPP development is trending jobs.
33 They test latests VPP build with latest oper branch of CSIT,
34 and analytics is applied to detect regressions in preformance.
35 For this to work properly, VPP project needs a warning against breaking
36 the assumptions the current oper branch makes about VPP behavior.
37 In the past, the most frequent type of such breakage was API change.
39 Earlier attempts to create a process to minimize breakage have focused
40 on creating a new verify job for VPP (called api-crc job) that
41 votes -1 on a change that affects CRC values for API messages CSIT uses.
42 The list of messages and CRC values (multiple "collections" are allowed)
43 is maintained in CSIT repository (in oper branch).
44 The process was less explicit on how should CSIT project maintain such list.
45 As CSIT was not willing to support two incpompatible API messages
46 by the same codebase (commit), there were unavoidable windows
47 where either trenging jobs, or CSIT verify jobs were failing.
49 Practice showed that human (or infra) errors can create two kinds of breakages.
50 Either the unavoidable short window gets long, affecting a trending job run
51 or two, or the api-crc job starts giving -1 to innocent changes
52 because oper branch went out of sync with VPP HEAD codebase.
53 This second type of failure prevents any merges to VPP for a long time
54 (12 hours is the typical time, give time zone differences).
56 The current version of this document introduces two new requirements.
57 Firstly, the api-crc job should not give false -1, under any
58 (reasonable) circumstances. That means, if a VPP change
59 (nor any of its unmerged ancestor commits) does not affect any CRC values
60 for messages used by CSIT, -1 should only mean "rebase is needed",
61 and rebasing to HEAD should result in +1 from the api-crc job.
62 Secondly, no more than one VPP change is allowed to be processed
67 It is easier to define the process after chosing shorter names
68 for notions that need long definition.
70 Note: Everytime a single job is mentioned,
71 in practice it can be a set of jobs covering parts of functionality.
72 A "run" of the set of jobs passes only if each job within the set
73 has been run (again) and passed.
77 + A *vpp verify* job: Any job run automatically, and voting on open VPP changes.
78 Some verify jobs compile and package VPP for target operating system
79 and processor architecture, the packages are NOT archived (currently).
80 They should be cached somewhere in future to speed up in downstream jobs,
81 but currently each such downstream job can clone and build.
83 + The *api-crc* job: Quick verify job for VPP changes, that accesses
84 CSIT repository (checkout latest oper branch HEAD) to figure out
85 whether merging the change is safe from CSIT point of view.
86 Here, -1 means CSIT is not ready. +1 means CSIT looks to be ready
87 for the new CRC values, but there still may be failures on real tests.
89 + A *trending* job: Any job that is started by timer and performs testing.
90 It checkouts CSIT latest oper branch HEAD, downloads the most recent
91 completely uploaded VPP package, and unconditionally runs the tests.
92 CRC checks are optional, ideally only written to console log
93 without otherwise affecting the test cases.
95 + A *vpp-csit* job: A slower verify job for VPP changes, that accesses CSIT
96 repository and runs tests from the correct CSIT commit (chosen as in trending)
97 against the VPP (built from the VPP patch under review).
98 Vote -1 means there were test failures. +1 means no test failures, meaning
99 there either was no API change, or it was backward compatible.
101 + A *csit-vpp* job: Verify job for open CSIT changes. Downloads the
102 (completely uploaded) VPP package marked as "stable", and runs a selection
103 of tests (from the CSIT patch under review).
104 Vote +1 means all tests have passed, so it is safe to merge
105 the patch under review.
107 + A *patch-on-patch* job: Manually triggered non-voting job
108 for open CSIT changes. Compiles and packages from VPP source
109 (usually of an unmerged change). Then runs the same tests as csit-vpp job.
110 This job is used to prove the CSIT patch under review is supporting
111 the specified VPP code.
112 In practice, this can be a vpp-csit job started with CSIT_REF set.
114 + A *manual verification* is done by a CSIT committer, locally executing steps
115 equivalent to the patch-on-patch job. This can to save time and resources.
119 Any commit in/for the CSIT repository contains a file (supported_crcs.yaml),
120 which contains either one or two collections. A collection is a mapping
121 that maps API message name to its CRC value.
123 A collection name specifies which VPP build is this collection for.
124 An API message name is present in a collection if and only if
125 it is used by a test implementation (can be in different CSIT commit)
126 targeted at the VPP build (pointed out by the collection name).
128 + The *stable collection*: Usually required, listed first, has comments and name
129 pointing to the VPP build this CSIT commit marks as stable.
130 The stable collection is only missing in deactivating changes (see below)
131 when not mergeable yet.
133 + The *active collection*: Optional, listed second, has comments and name
134 pointing to the VPP Gerrit (including patch set number)
135 the currently active API process is processing.
136 The patch set number part can be behind the actual Gerrit state.
137 This is safe, because api-crc job on the active API change will fail
138 if the older patch is no longer API-equivalent to the newer patch.
142 + An *API change*: The name for any Gerrit Change for VPP repository
143 that does not pass api-crc job right away, and needs this whole process.
144 This usually means .api files are edited, but a patch that affects
145 the way CRC values are computed is also an API change.
147 Full name could be VPP API Change, but as no CSIT change is named "API change"
148 (and this document does not talk about other FD.io or external projects),
149 "API change" is shorter.
151 + A *blocked change*: The name for open Gerrit Change for VPP repository
152 that got -1 from some of voting verify jobs.
154 + A *VPP-blocked change": A blocked change which got -1 from some "pure VPP"
155 verify job, meaning no CSIT code has been involved in the vote.
156 Example: "make test" fails.
158 VPP contributor is expected to fix the change, or VPP developers
159 are expected to found a cause in an earlier VPP change, and fix it.
160 No interaction with CSIT developers is necessary.
162 + A *CSIT-blocked change*: A blocked change which is not VPP-blocked,
163 but does not pass some vpp-csit job.
164 To fix a CSIT-blocked change, an interaction with a CSIT committer
165 is usually necessary. Even if a VPP developer is experienced enough
166 to identify the cause of the failure, a merge to CSIT is usually needed
169 This process does not specify what to do with CSIT-blocked changes
170 that are not also API changes.
172 + A *candidate API change*: An API change that meets all requirements
173 to become active (see below). Currently, the requirements are:
175 + No -1 nor -2 from from any human reviewer.
177 + All verify jobs (except vpp-csit ones) pass.
179 + +1 from a VPP committer.
181 The reason is to avoid situations where an API change becomes active,
182 but the VPP committers are unwilling to merge it for some reason.
184 + The *active API change*: The candidate API change currently being processed
185 by the API Flag Day Algorithm.
186 While many API changes can be candidates at the same time,
187 only one is allowed be active at a time.
189 + The *activating change*: The name for a Gerrit Change for CSIT repository
190 that does not change the test code, but adds the active CRC collection.
191 Merge of the opening change (to latest CSIT oper branch) defines
192 which API change has become active.
194 + The *deactivating change*: The name for Gerrit Change for CSIT repository
195 that only supports tests and CRC values for VPP with the active API change.
196 That implies the previously stable CRC collection is deleted,
197 and any edits to the test implementation are done here.
199 + The *mergeable deactivating change*: The deactivating change with additional
200 requirements. Details on the requirements are listed in the next section.
201 Merging this change finishes the process for the active API change.
203 It is possible for a single CSIT change to act both as a mergeable
204 deactivating change for one API change, and as an activating change
205 for another API change. As English lacks a good adjective for such a thing,
206 this document does not name this change.
207 When this documents says a change is activating or deactivating,
208 it allows the possibility for the change to fullfill also other purposes
209 (e.g. acting as deactivating / activating change for another API change).
213 The following steps describe the application of the API "Flag Day" algorithm:
215 #. A VPP patch for an API change is submitted to
217 #. The api-crc job detects the API CRC values have changed
218 for some messages used by CSIT.
219 #. The api-crc job runs in parallel with any other vpp-csit verify job,
220 so those other jobs can hint at the impact on CSIT.
221 Currently, any such vpp-csit job is non-voting,
222 as the current process does not guarantee such jobs passes
223 when the API change is merged.
224 #. If the api-crc job fails, an email with the appropriate reason
225 is sent to the VPP patch submitter and vpp-api-dev@lists.fd.io
226 including the VPP patch information and .api files that are edited.
227 #. The VPP patch developer works with a VPP committer
228 to ensure the patch meets requirements to become a candidate (see above).
229 #. The VPP patch developer and CSIT team create a CSIT JIRA ticket
230 to identify the work required to support the new VPP API version.
231 #. CSIT developer creates a patch of the deactivating change
232 (upload to Gerrit not required yet).
233 #. CSIT developer runs patch-on-patch job (or manual verification).
234 Both developers iterate until the verification passes.
235 Note that in this phase csit-vpp job is expected to vote -1,
236 as the deactivating change is not mergeable yet.
237 #. CSIT developer creates the activating change, uploads to Gerrit,
238 waits for vote (usual review cycle applies).
239 #. When CSIT committer is satisfied, the activating change is merged
240 to CSIT master branch and cherry-picked to the latest oper branch.
241 This enters a "critical section" of the process.
242 Merges of other activating changes are not allowed from now on.
243 The targeted API change becomes the active API change.
244 This does not break any jobs.
245 #. VPP developer (or CSIT committer) issues a recheck on the VPP patch.
246 #. On failure, VPP and CSIT committers analyze what went wrong.
247 Typically, the active CRC collection is matching only an older patch set,
248 but a newer patch set needs different CRC values.
249 Either due to improvements on the VPP change in question,
250 or due to a rebase over previously merged (unrelated) API change.
251 VPP perhaps needs to rebase, and CSIT definitely needs
252 to merge edits to the active collection. Then issue a recheck again,
253 and iterate until success.
254 #. On success, VPP Committer merges the active API change patch.
255 (This is also a delayed verification of the current active CRC collection.)
256 #. VPP committer sends an e-mail to vpp-api-dev stating the support for
257 the previous CRC values will soon be removed, implying other changes
258 (whether API or not) should be rebased soon.
259 #. VPP merge jobs create and upload new VPP packages.
260 This breaks trending jobs, but both VPP and CSIT verify jobs still work.
261 #. CSIT developer makes the deactivating change mergeable:
262 The stable VPP build indicator is bumped to the build
263 that contains the active API change. The active CRC collection
264 (added by the activating change) is renamed to the new stable collection.
265 (The previous stable collection has already been deleted.)
266 At this time, the deactivating change should be uploaded to Gerrit and
267 csit verify jobs should be triggered.
268 #. CSIT committer reviews the code, perhaps triggering any additional jobs
269 needed to verify the tests using the edited APIs are still working.
270 #. When satisfied, CSIT committer merges the mergeable deactivating change
271 (to both master and oper).
272 The merge fixes trending jobs. VPP and CSIT verify jobs continue to work.
273 The merge also breaks some verify jobs for old changes in VPP,
274 as announced when the active API change was merged.
275 The merge is the point where the process leaves the "critical section",
276 thus allowing merges of activating changes for other API changes.
277 #. CSIT committer sends an e-mail to vpp-api-dev stating the support for
278 the previous CRC values has been removed, and rebase is needed
279 for all affected VPP changes.
280 #. Recheck of existing VPP patches in gerrit may cause the "VPP
281 API Incompatible Change Test" to send an email to the patch
282 submitter to rebase the patch to pick up the compatible VPP API
285 ### Real life examples
287 Simple API change: https://gerrit.fd.io/r/c/vpp/+/23829
289 Activating change: https://gerrit.fd.io/r/c/csit/+/23956
291 Mergeable deactivating change: https://gerrit.fd.io/r/c/csit/+/24280
293 Less straightforward mergeable deactivating change:
294 https://gerrit.fd.io/r/c/csit/+/22526
297 + Crc edits: supported_crcs.yaml
298 + Version bump: VPP_STABLE_VER_UBUNTU_BIONIC
299 + And even a way to work around failing tests:
300 eth2p-ethicmpv4-ip4base-eth-1tap-dev.robot
302 Simple change that is both deactivating and activating:
303 https://gerrit.fd.io/r/c/csit/+/23969