LUCI Change Verifier

LUCI Change Verifier (CV) is the LUCI microservice that is replacing LUCI CQDaemon, while providing the same or better functionality.

CV is already responsible for starting and completing the Runs, which includes CL Submission.

As of August 2021, CV work group is working on second milestone moving the remaining functionalities off CQDaemon and onto CV (tracking bug https://crbug.com/1225047).

TODO(crbug.com/1225047): update this doc.

What's here?

• api: Protobuf files specifying the public API of CV, such as per-project config spec, PubSub messages and RPCs definitions. APIs organization is a bit messy right now, but of note are 2 versions:
  • v0: experimental API under development. Request an approval from CV owners before using it.
  • v1: stable API, which won‘t be broken unless absolutely necessary. As of Sep 2021, it’s under the development.
• appengine: the entry point for a GAE app.
  • appengine/templates: HTML templates for debug web-based UI of CV. These are rendered by internal/userhtml Go package.
  • appengine/static: static resources loaded by web UI directly.
• internal: GAE-agnostic implementation details in Go. See godoc-based overview here. Notably:
  • internal/cvtesting/e2e high level end-to-end level CV tests, which cover the most important business logic in a fairly readable and concise way. The test are run against a fake Gerrit.
  • internal/changelist: encapsulates a changelist (a.k.a. CL, patch, Gerrit Change).
  • internal/acls: enforces ALCs.
  • internal/tryjob: manages tryjobs (i.e. Buildbucket builds) which are used to verify a CL.
  • internal/prjmanager and sub-packages: decides when to start new Runs given the state of all CLs in an individual LUCI project.
  • internal/run and sub-packages: handles individual Run from its creation to completion.
  • internal/rpc pRPC handlers, including “admin” API not exposed in public api dir.

Developer Guide

Error handling guide

Like all other LUCI go code:

• SHOULD wrap errors with errors.Annotate to provide additional context. Unlike other error-wrapping packages, it also captures the call stack.

• SHOULD avoid ignoring errors. If it's justified, add a comment in code and if necessary log the error.

• SHOULD use appstatus on errors in RPC-handling codepaths.

LUCI CV also follows these conventions, which in some cases differ from other LUCI Go code:

• SHOULD use CV‘s common.LogError(ctx, err) for logging error + stack trace instead of errors.Log(ctx, err). The CV’s version packs the entire stack into as few log entries as possible, leading to a better debugging experience with Cloud Logging.

• Tag the error with transient.Tag if the function call can succeed on a retry. For example, most Datastore errors different from NoSuchEntity SHOULD be thus tagged.

• SHOULD use common.TQifyError or its custom version common.TQIfy{...}.Error(ctx, err) before returning from a TQ task handler. This func logs the error with appropriate severity and with stack trace as necessary (via common.LogError). Additionally, it converts the error to an appropriate server/tq tag as needed. The custom common.TQIfy SHOULD be used to reduce noise in logs and oncall alerting from the frequent errors during normal operation which don't critically harm the service, e.g. “ErrStaleGerritData”.

• MAY panic when a function precondition fails, e.g. sqrt(x) may panic if x is negative. This is like an assert in Python / C / C++, which is contrary to Go's standard guidance.

• MUST return a singular error from a function instead of errors.MultiError or similar multi-error holders unless all of the below hold true, which was so far very rare in CV code:

  • the function signature clearly states that a multi-error is returned, e.g., func loadMany(clids ... int64) ([]*CL, errors.MultiError);
  • the caller must examine each individual error, e.g. choosing to create missing CLs based on loadMany() errors;
  • no transient.Tag or annotation attached to the mutli-error itself, though an individual sub-error may have them.

• SHOULD use common.MostSevereError on a multi-error before returning. For example, a common pattern to choose 1 error after parallelizing is return common.MostSevereError(parallel.FanOut(...));

  • Individual errors which are thus ignored MAY be logged. This isn't required because in practice most such errors are usually correlated, and the most severe one is thus typically sufficient for debugging.

Full end to end testing of new features

1. Land your code, which gets auto-deployed to luci-change-verifier-dev project, You may also just upload a tainted version and switch all traffic to it, but beware that the next auto-deployment will override it. Thus, adding unit- and e2e tests with fake Gerrit and Cloud dependencies is a good first step and at times cheaper/faster to do.

2. cq-test LUCI project can be used for any such tests. It‘s already connected to only luci-change-verifier-dev. The cq-test project’s config tells CV to watch 2 repositories:

   • https://chromium.googlesource.com/playground/gerrit-cq/
   • https://chrome-internal.googlesource.com/playground/cq/
     • This repo also hosts the LUCI config for the cq-test.

   Creating a CL on refs/heads/main will use combinable config group, meaning multi-CL Runs in ChromeOS style can be created. For single-CL Runs, create CLs on refs/heads/single ref:

       git new-branch --upstream origin/single
       echo "fail, please" > touch_to_fail_tryjob
       echo "fail with INFRA_FAILURE, please" > touch_to_infra_fail_tryjob
       git commit -a -m "test a signle CL dry run with failing tryjobs"
       git cl upload -d
   

   You can see recent Runs in https://luci-change-verifier-dev.appspot.com/ui/recents/cq-test.

3. (Optional) internal/cvtesting/e2e/manual contains tools to automate common tasks, e.g. creating and CQ-ing large CL stacks. Feel free to contribute :)

UI

tl;dr

cd appengine
go run main.go
# See output for URLs to http URLs.

To work with Runs from the -dev project, connect to its Datastore by adding these arguments:

go run main.go \
    -cloud-project luci-change-verifier-dev \
    -root-secret devsecret://base64anything \
    -primary-tink-aead-key devsecret-gen://tink/aead

NOTE: if you want the old page tokens to work on subsequent go run main.go ... invocations, when you first invoke it, observe output of the first invocation which should mention a devsecret://veeeeeeeeeeeeeeery-looooooong-base64-line, which you can use on subsequent invocations instead of devsecret-gen://tink/aead.

For a quick check, eyeball these two pages (your port may be different):

• http://localhost:8800/ui/run/cq-test/8991920303854-1-19bc46b6c6972e90
• http://localhost:8800/ui/recents/cq-test

Finally, you can deploy your work-in-progress to -dev project directly.

How does this code end up in production?

tl;dr this the usual way for LUCI GAE apps. Roughly,

1. CL lands in luci-go (this) repo.

2. Autoroller rolls it into infra/infra repo (example).

   • pro-tip: If autoroller is stuck, you can create your own DEPS roll with roll-dep go/src/go.chromium.org/luci in your infra/infra checkout.

3. Tarball with only the necessary files is created by the Google-internal infra-gae-tarballs-continuous builder.

4. Newest tarball is automatically rolled into also Google-internal infradata-gae repo (example).

5. Google-internal gae-deploy builder auto-deploys the newest tarball to luci-change-verifier-dev GAE project.

6. Someone manually bumps tarball version to deploy to production luci-change-verifier via a CL (example).

   • Recommended use bump-dev-to-prod.py tool to make such a CL. For example,

     cd gae/app/luci-change-verifier
     ./bump-dev-to-prod.py -- --bug $BUG -r <REVIEWER> -d -s
     

7. The same Google-internal gae-deploy builder deploys the desired version to production luci-change-verifier GAE project.

LUCI CV Command Line utils

LUCI Change Verifier provides a command line interface luci-cv intended for LUCI integrators to debug CV configurations.

Getting the luci-cv CLI binary.

There are two ways of getting the latest version of the binary at the moment:

• Building it yourself from this package: go.chromium.org/luci/cv/cmd/luci-cv e.g.

  go build go.chromium/org/luci/cv/cmd/luci-cv
  

• Getting it from CIPD e.g. via a command such as:

  cipd ensure -ensure-file - -root cv-cli <<< 'infra/tools/luci-cv/${platform} latest'
  

For the appropriate syntax and flags information refer to the binary's built-in documentation. e.g. luci-cv help match-config.

Examples

Check if CL is watched by CV and which config group applies

# (Assuming luci-cv was installed in the current dir)
~/infra/infra$ ./luci-cv match-config infra/config/generated/commit-queue.cfg https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3214613

https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3214613:
  Location: Host: chromium-review.googlesource.com, Repo: infra/luci/luci-go, Ref: refs/heads/main
  Matched: luci-go

Links

• The legacy CQDaemon code is in infra_internal.
• Additional Google-internal docs are found at go/luci/cq.