docs/branch_sheriff.md - chromium/src.git - Git at Google

 # Chromium Branch Sheriffing

 This document describes how to be a Chromium *branch* sheriff and how sheriffing
 on a branch differs from sheriffing on trunk. For trunk sheriffing guidance, see
 [//docs/sheriff.md][sheriff-md].

 [TOC]

 ## Philosophy

 The goals of a branch sheriff are quite similar to those of a trunk sheriff.
 Branch sheriffs need to ensure that:

 1. **Compile failures get fixed**, because compile failures on branches block
 all tests (both automated and manual) and consequently reduce our confidence
 in the quality of what we're shipping, possibly to the point of blocking
 releases.
 2. **Consistent test failures get repaired**, because they similarly reduce
 our confidence in the quality of our code.

 **Communication** is important for sheriffs in general, but it's particularly
 important for branch sheriffs. Over the course of your shift, you may need to
 coordinate with trunk sheriffs, troopers, release TPMs, and others -- don't
 hesitate to do so, particularly if you have questions.

 Points of contact (i.e. platform-specific sheriffs) can be found
 [here](http://goto.google.com/chrome-branch-sheriffing#points-of-contact).

 ## Processes

 In general, you'll want to follow the same processes outlined in
 [//docs/sheriff.md][sheriff-md]. There are some differences, though.

 ### Checkout

 You'll need to ensure that your checkout is configured to check out the branch
 heads. You can do so by running

 ```
   src $ gclient sync --with_branch_heads
 ```

 > This only needs to be done once, though running it more than once won't hurt.

 You may also need to run:

 ```
   src $ git fetch
 ```

 Once you've done that, you'll be able to check out branches:

 ```
   src $ git checkout branch-heads/$BRANCH_NUMBER  # e.g. branch-heads/4044 for M81
   src $ gclient sync
 ```

 To determine the appropriate branch number, you can either use
 [chromiumdash](#chromiumdash) or check [milestone.json][milestone-json]
 directly.

 ### Findit

 As FindIt is not available on branches, one way to try to find culprits is using
 `git bisect` locally and upload changes to a gerrit CL and run the needed
 trybots to check. This is especially useful when the errors are not reproducible
 on your local builds or you don't have the required hardware to build the failed
 tests.

 ### Flaky tests

 Flaky tests that are disabled on trunk should also be disabled on any branches
 with frequent failures of that test. If a trunk CL lands with no change other
 than to disable one or more tests ([example](https://crrev.com/c/2507299)) and
 it has an associated bug and the release manager is cc'd on the bug, you can and
 should cherrypick it to the affected branch without requesting merge approval.

 On the other hand, if you believe that a flake was introduced by a cherry-pick
 to the branch in question and is not flaky on trunk, you will need to create a
 new CL to disable it only on the branch and go through the usual merge request
 process.

 Note: there is little value in merging changes to the stable release
 branch when the next milestone's stable release is less than a week away
 (since there are usually no planned stable respins at that point).
 You can find release dates on [chromiumdash][chromiumdash-schedule].

 ### Landing changes

 When you need to land a change to a branch, you'll need to go through [the same
 merge approval process](./process/merge_request.md) as other cherry-picks (see
 exception for flaky tests above). You should feel free to ping the relevant
 release TPM as listed on [chromiumdash][chromiumdash-schedule].

 ## Tools

 ### Sheriff-o-Matic

 Use the [branch SoM console][sheriff-o-matic] rather than the main chromium
 console.

 ### Consoles

 Use the [beta][main-beta] and [stable][main-stable] branch consoles rather than
 the main console. A new console is created for each milestone. They are named
 "Chromium M## Console" and can be found under the
 [Chromium Project](https://ci.chromium.org/p/chromium).

 ### Monorail issues (crbug)

 Refer and use the
 [Sheriff-Chrome-Release label](https://bugs.chromium.org/p/chromium/issues/list?q=label%3ASheriff-Chrome-Release)
 to find and tag issues that are of importance to Branch sheriffs.

 ### Chromiumdash

 [chromiumdash][chromiumdash] can help you determine the branch number for a
 particular milestone or channel, along with a host of other useful information:

   * [Branches][chromiumdash-branches] lists the branches for each milestone.
   * [Releases][chromiumdash-releases] lists the builds currently shipping to
     each channel, which can help map from channel to milestone or to branch.
   * [Schedule][chromiumdash-schedule] lists the relevant dates for each
     milestone and includes the release TPMs responsible for each milestone by
     platform.

 ### Rotation

 The current branch sheriff is listed [here][rotation-home]. The configuration
 and source of truth for the schedule lives [here][rotation-config]. To swap,
 simply send a CL changing schedule at the bottom of the file.
 You can also use [Oncall Swapper](https://oncallswapper.corp.google.com/)
 to find the swap and submit the CL for you.

 [chromiumdash]: https://chromiumdash.appspot.com
 [chromiumdash-branches]: https://chromiumdash.appspot.com/branches
 [chromiumdash-releases]: https://chromiumdash.appspot.com/releases
 [chromiumdash-schedule]: https://chromiumdash.appspot.com/schedule
 [main-beta]: https://ci.chromium.org/p/chromium/g/main-m81/console
 [main-stable]: https://ci.chromium.org/p/chromium/g/main-m80/console
 [milestone-json]: https://goto.google.com/chrome-milestone-json
 [rotation-home]: https://goto.google.com/chrome-branch-sheriff-amer-west
 [rotation-config]: https://goto.google.com/chrome-branch-sheriff-amer-west-config
 [sheriff-md]: /docs/sheriff.md
 [sheriff-o-matic]: https://sheriff-o-matic.appspot.com/chrome_browser_release
	# Chromium Branch Sheriffing

	This document describes how to be a Chromium branch sheriff and how sheriffing
	on a branch differs from sheriffing on trunk. For trunk sheriffing guidance, see
	[//docs/sheriff.md][sheriff-md].

	[TOC]

	## Philosophy

	The goals of a branch sheriff are quite similar to those of a trunk sheriff.
	Branch sheriffs need to ensure that:

	1. Compile failures get fixed, because compile failures on branches block
	all tests (both automated and manual) and consequently reduce our confidence
	in the quality of what we're shipping, possibly to the point of blocking
	releases.
	2. Consistent test failures get repaired, because they similarly reduce
	our confidence in the quality of our code.

	Communication is important for sheriffs in general, but it's particularly
	important for branch sheriffs. Over the course of your shift, you may need to
	coordinate with trunk sheriffs, troopers, release TPMs, and others -- don't
	hesitate to do so, particularly if you have questions.

	Points of contact (i.e. platform-specific sheriffs) can be found
	[here](http://goto.google.com/chrome-branch-sheriffing#points-of-contact).

	## Processes

	In general, you'll want to follow the same processes outlined in
	[//docs/sheriff.md][sheriff-md]. There are some differences, though.

	### Checkout

	You'll need to ensure that your checkout is configured to check out the branch
	heads. You can do so by running

	```
	src $ gclient sync --with_branch_heads
	```

	> This only needs to be done once, though running it more than once won't hurt.

	You may also need to run:

	```
	src $ git fetch
	```

	Once you've done that, you'll be able to check out branches:

	```
	src $ git checkout branch-heads/$BRANCH_NUMBER # e.g. branch-heads/4044 for M81
	src $ gclient sync
	```

	To determine the appropriate branch number, you can either use
	[chromiumdash](#chromiumdash) or check [milestone.json][milestone-json]
	directly.

	### Findit

	As FindIt is not available on branches, one way to try to find culprits is using
	`git bisect` locally and upload changes to a gerrit CL and run the needed
	trybots to check. This is especially useful when the errors are not reproducible
	on your local builds or you don't have the required hardware to build the failed
	tests.

	### Flaky tests

	Flaky tests that are disabled on trunk should also be disabled on any branches
	with frequent failures of that test. If a trunk CL lands with no change other
	than to disable one or more tests ([example](https://crrev.com/c/2507299)) and
	it has an associated bug and the release manager is cc'd on the bug, you can and
	should cherrypick it to the affected branch without requesting merge approval.

	On the other hand, if you believe that a flake was introduced by a cherry-pick
	to the branch in question and is not flaky on trunk, you will need to create a
	new CL to disable it only on the branch and go through the usual merge request
	process.

	Note: there is little value in merging changes to the stable release
	branch when the next milestone's stable release is less than a week away
	(since there are usually no planned stable respins at that point).
	You can find release dates on [chromiumdash][chromiumdash-schedule].

	### Landing changes

	When you need to land a change to a branch, you'll need to go through [the same
	merge approval process](./process/merge_request.md) as other cherry-picks (see
	exception for flaky tests above). You should feel free to ping the relevant
	release TPM as listed on [chromiumdash][chromiumdash-schedule].

	## Tools

	### Sheriff-o-Matic

	Use the [branch SoM console][sheriff-o-matic] rather than the main chromium
	console.

	### Consoles

	Use the [beta][main-beta] and [stable][main-stable] branch consoles rather than
	the main console. A new console is created for each milestone. They are named
	"Chromium M## Console" and can be found under the
	[Chromium Project](https://ci.chromium.org/p/chromium).

	### Monorail issues (crbug)

	Refer and use the
	[Sheriff-Chrome-Release label](https://bugs.chromium.org/p/chromium/issues/list?q=label%3ASheriff-Chrome-Release)
	to find and tag issues that are of importance to Branch sheriffs.

	### Chromiumdash

	[chromiumdash][chromiumdash] can help you determine the branch number for a
	particular milestone or channel, along with a host of other useful information:

	* [Branches][chromiumdash-branches] lists the branches for each milestone.
	* [Releases][chromiumdash-releases] lists the builds currently shipping to
	each channel, which can help map from channel to milestone or to branch.
	* [Schedule][chromiumdash-schedule] lists the relevant dates for each
	milestone and includes the release TPMs responsible for each milestone by
	platform.

	### Rotation

	The current branch sheriff is listed [here][rotation-home]. The configuration
	and source of truth for the schedule lives [here][rotation-config]. To swap,
	simply send a CL changing schedule at the bottom of the file.
	You can also use [Oncall Swapper](https://oncallswapper.corp.google.com/)
	to find the swap and submit the CL for you.

	[chromiumdash]: https://chromiumdash.appspot.com
	[chromiumdash-branches]: https://chromiumdash.appspot.com/branches
	[chromiumdash-releases]: https://chromiumdash.appspot.com/releases
	[chromiumdash-schedule]: https://chromiumdash.appspot.com/schedule
	[main-beta]: https://ci.chromium.org/p/chromium/g/main-m81/console
	[main-stable]: https://ci.chromium.org/p/chromium/g/main-m80/console
	[milestone-json]: https://goto.google.com/chrome-milestone-json
	[rotation-home]: https://goto.google.com/chrome-branch-sheriff-amer-west
	[rotation-config]: https://goto.google.com/chrome-branch-sheriff-amer-west-config
	[sheriff-md]: /docs/sheriff.md
	[sheriff-o-matic]: https://sheriff-o-matic.appspot.com/chrome_browser_release