gerrit+ci improvement proposal

[Max Kovgan]

Hi everyone!
We really want to have reliable and snappy CI: to allow short cycles and encourage developers to write tests.

# Problem

Many patches are neither ready for review nor for CI upon submission, which is OK.
But running all the jobs on those patches with limited resources results in: overloaded resources, slow response time, unhappy developers.

# Proposed Solution

To run less jobs we know we don’t need to, thus making more resources for the jobs we need to run.
We have been experimenting to make our CI stabler and quicker to respond by using gerrit flags. This has improved in both directions very well internally.
Now it seems a good time to let all the oVirt projects to use this.
This solution indirectly promotes reviews and quick tests - “to fail early”, yet full blown static code analysis and long tests to run “when ready”.

# How it works

2 new gerrit independent flags are added to gerrit.

## CI flag

Will express patch CI status. Values:
 * +1 CI passed
 *  0 CI did not run yet
 * -1 CI failed
Permissions for setting: project maintainers (for special cases) should be able to set/override (except Jenkins).

## Workflow flag

Will express patch “workflow” state. Values:
 *  0 Work In Progress
 * +1 Ready For Review
 * +2 Ready For Merge
Permissions for setting: Owner can set +1, Project Maintainers can set +2

## Review + CI Integration:

Merging [“Submit” button to appear] will require: Review+1, CI+1, Workflow+2
Patch lifecycle now is:
---------------------------------------------------------------
patch state   |owner     |reviewer |maintainer |CI tests |pass
---------------------------------------------------------------
added/updated |-         |-        |-          |quick    |CI+1
review        |Workflow+1|Review+1 |-          |heavy	 |CI+1
merge ready   |-         |-        |Workflow+2 |gating   |CI+1
merge         |-         |-        |merge      |merge    |CI+1

Changes from current workflow:
Owner only adds reviewers, now owner needs to set "Workflow+1" for the patch to be reviewed, and heavily auto-tested.
Maintainer now needs to set "Workflow+2" and wait for "Submit" button to appear after CI has completed running gating tests.


Next step will be to automate merge the change after Workflow+2 has been set by the Maintainer and gating tests passed.


## Why now?

It is elimination of waste. The sooner - the better. 
The solution has been used for a while and it works. 
Resolving the problem without gerrit involved will lead to adding unreliable code into jobs, and will still be prone to problems:
  Just recently, 3d ago we’ve tried detecting what to run from jenkins relying only on gerrit comments so that upon Verified+1, we’d run the job.
  We could not use “Review+1”, because it makes no sense at all, so we left the job to set Verified+1.
  Meaning - re-trigger itself immediately more than 1 times.
  
  Jenkins and its visitors very unhappy, and we had to stop those jobs, clean up the queue, and spam developers.

## OK OK OK. Now what?

Now we want your comments and opinions before pushing this further:
Please participate in this thread, so we can start trying it out.
Ask, Suggest better ideas, all this is welcome.


Best Regards!


N.B.
Of course, this is not written in stone, in case we find a better approach on solving those issues, we will change to it.
And we will keep improving so don't be afraid that it will be enforced: if this does not work out we will discard it.

P.S.
Kudos to dcaro, most of the work was done by him, and most of this text too.




Max Kovgan

Senior Software Engineer
Red Hat - EMEA ENG Virtualization R&D
Tel.: +972 9769 2060
Email: mkovgan [at] redhat [dot] com
Web: http://www.redhat.com
RHT Global #: 82-72060