[Kde-pim] Problems with infrastructure

Jan Kundr√°t jkt at kde.org
Tue Dec 16 21:23:26 GMT 2014


Hi Ben,

> It isn't just
> the tool itself which has to be maintained: we have commit hooks,
> integration with other bits of infrastructure and so forth which also
> needs to both be implemented and maintained.

In case of Gerrit, there is no need for custom hooks as they stay on 
git.kde.org, and therefore I believe this point is not relevant to its 
adoption. The whole setup has been designed and implemented in a way 
suitable for long-term parallel operation alongside KDE's git.

As for the integration bits, they're done now. The tool just talks to LDAP, 
and maintenance of that connection is effectively zero, unless a dramatic 
revamp of our LDAP is planned. The repo mirroring was a matter of setting 
up a single user account and configuring proper ACLs, and these are also 
finished already.

I can understand the general reasons for limitting the number of services 
which we offer and support. However, I would appreciate if we mentioned how 
big these costs are, as there's some room of misinterpretation otherwise.

> The more custom work we have, the harder it is to upgrade things.

While true in general, I fail to see how it is relevant to Gerrit. What 
custom bits are involved here?

> We'll confuse newcomers if
> projects A, B and C are reviewed on tool X while projects D, E and F
> are reviewed on tool Y.

I haven't received a single complaint from the Trojita GCI students about 
any hardness in this. They did struggle with making an actual change to the 
code, with proper coding style, with commit message formatting, with git in 
general, they even failed to understand the written text about CCBUG and 
BUG keywords in the our wiki, but nope, I haven't seen them struggle with a 
need to use Gerrit or its differences to RB. YMMV, of course.

Because the majority of complaints actually came from people who are 
well-versed with ReviewBoard, my best guess is that there's muscle memory 
at play here. This is supported by an anecdote -- when I was demoing the RB 
interface to a colleague who maintains Gerrit at $differentOrg, we both 
struggled with finding buttons for managing a list of issues within RB. 
It's been some time since I worked with RB, and it showed.

I remember having hard time grokking the relation between a "review" and 
"attaching/updating a file" on RB. I didn't read the docs, and it showed.

> A single tool would be best here. Let me make
> clear that it is not a case of Reviewboard vs. Gerrit here - as other
> options need to be evaluated too.

I understand that people would like to avoid migrating to Gerrit if a 
migration to a $better-tool was coming. Each migration hurts, and it makes 
a lot of sense to reduce the number of hops.

However, what I'm slightly worried about is postponing Gerrit indefinitely 
until all future replacements are evaluated. I don't see people putting 
significant time into any alternative for code review right now. Do we have 
any chances of these people making themselves known in close future? How 
long would be a reasonable waiting time for a testing deployment of 
alternate tools? When are we going to reduce our candidates just to the 
contenders which have been deployed and tested by some projects?

> In regards to the difficulty of Gerrit - I tend to agree with this
> argument (it took me at least a minute to find the comment button, and
> I didn't even get to reviewing a diff).

The documentation, however, explains the functionality in a pretty clean 
manner, see 
https://gerrit.vesnicky.cesnet.cz/r/Documentation/user-review-ui.html .

We also aren't the first project trying to work with Gerrit, so there's 
plenty of tooling available right now, not "to be written". There's 
text-mode interface, the "gertty" project, there's integration in 
QtCreator, there are pure-CLI tools for creating reviews, another web UIs 
in development, there are even Android clients.

> Plus there are major concerns
> with integration into our infrastructure, such as pulling SSH keys
> from LDAP for instance (no, you can't have the tool maintain them
> itself - as mainline Git and Subversion need the keys too).

Yes, SSH-keys-in-LDAP is a PITA, but given that one needs a patched OpenSSH 
to look up keys from LDAP anyway, I don't think this is a blocker issue. 
The situation is exactly the same with the Gitolite setup which currently 
runs on git.k.o though, as that doesn't talk to LDAP either. As you 
mentioned during our IRC chat, there's a Python daemon which polls for 
changes in LDAP, and propagates these into Gitolite's config backend in a 
non-public git repo. Why wouldn't this be enough for Gerrit, then?

Gerrit has both SSH-authenticated API and a REST HTTPS API for adding and 
removing of SSH keys by an admin account. *If* this is needed, I'll be 
happy to make it work, it's simply a matter of calling two trivial scripts. 
Would you see any problems with hooking into the identity webapp or its 
backend, if there's any, for this? An edge trigger would be cool.

Are there any other concerns?

> Please note that any discussion of tools should be on the merits of
> the tools themselves. Things like CI integration are addons, which
> both Reviewboard and Gerrit are capable of.

With varying levels of ease, I should add. In the end, everything is 
achievable, and you can write tools which automatically pull patches sent 
through mailing lists and build that, but the question is who is going to 
do the work, and when it's going to be ready. I know that the CI+Gerrit 
thing is now done and solved, and I also know that I won't be spending my 
time in redoing the same for ReviewBoard. Nobody bothered to do this 
pre-merge CI for RB in the past years. Do we have some volunteers now?

> The only reason we don't
> have Reviewboard integration yet is a combination of technical issues
> (lack of SNI support in Java 6)

And nobody caring enough to do the work, I suppose. AFAIK Jenkins runs on 
Java 7 just fine, but apparently nobody found time for such an upgrade. 
There's nothing bad with this, of course, but it doesn't suggest that 
suddenly these people will have time for setting up early CI with RB.

> and resource ones (some projects take
> a long time to complete, and i'm concerned we don't have the
> processing power).

This is not really an all-or-nothing question. If there's a project which 
exceeds our current HW possibilities (you mentioned Calligra before, 
right?) and we cannot easily get more HW (did someone ask the foundation's 
treasurers for funds for HW rental, or approached some of the obvious 
candidates such as RedHat or SuSE asking for HW access?), perhaps that 
project can simply be omitted from these pre-merge CI runs.

We've chatted a couple of times about the limits of the current CI setup, 
about its inability to perform checks in parallel. Is the existing 
architecture going to scale with these pre-merge CI runs without 
substantial changes?

Again, this is something which is solved now with the CI setup that is 
behind Gerrit. The changes were into the glue code, the code which 
schedules the builds, distributes the jobs and which decides when to build 
what. It's still using the KDE CI's Python scripts for managing library 
deps and for actually launching the build (I sent the necessary patches 
your way).

> In terms of a modern and consistent project tool - I agree here. A
> long term todo item of sysadmin is to replace projects.kde.org. The
> question is of course - with what. Chiliproject is now unmaintained,
> so we do have to migrate off to another solution at some point. If the
> new tool happens to be more integrated in terms of code review, that
> is a bonus from my point of view (as it means the integration will be
> better, and there is one less piece of infrastructure to maintain).

See above for my view of mixing the quest for finding a decent project 
management tool and for finding a good code review system. To go a bit to 
the meta side, IMHO, a universal tool which does plenty of things in a 
not-excellent manner is worse than using diverse set of tools which do one 
thing each, and do it well. That's why I see a Chilliproject replacement to 
be an orthogonal topic to the choice of a code review tool.

> @Jan: could you please outline what you consider to be the key
> advantages? At the moment I understand that you are after:
>
> 1) CI integration to pre-validate the change before it gets reviewed

- With the CI actually testing not just the change in isolation (as a 
result of it on top of what was at the repo at the time the change was 
made), but the result of the change as applied to the current state of the 
repo at merge time, and with user-visible possibility of retruggering a 
check job.

- Being able to do "trunk gating" for projects which care enough. That is, 
there's a tool which makes sure that there are no regressions, and which 
won't let in commits which break the build or cause tests to fail. (And 
yes, I know that there'll always be an option of direct pushes, I am not 
pushing against that, it appears to be a point which people require. OK 
with me.)

- Being able to do cross-project verification, i.e. "does this change of 
kio break plasma-framework?"

- Performing builds on various base OSes, against the Qt version provided 
by system (Trojita aims at supporting Qt 4.6-4.8 and 5.2+), using ancient 
compilers (yes, C++11 and GCC 4.4 are so much fun when taken together) and 
different mixes of optional dependencies and features to be built. In 
short, testing in the env people will be using, including Windows and Mac 
OS X.

> 2) Ability to directly "git pull" the patch (which Phabricator's arc
> tool would meet I believe?)

With Gerrit, one has an access to the full history of each change, 
including accessing them in offline mode. This is opt-in, so people who 
don't care will not have their clones "polluted by this nonsense", while 
people who do care have them "enhanced by this valuable data". This happens 
with no extra tooling. I'm sure I could come up with e.g. local scripts 
that build these git refs from the (history of) patches on RB, Phabricator, 
GitHub, Gitorious or whatever, but native support trumps scripting each 
time.

According to the docs, `arc` is something which just pushes patches around. 
Working with patches is different from having a git ref to work on.

Have you ever used OpenSUSE's Build Service and its CLI client, the `osc`? 
That's what happens when one tries to reimplement a SCM when working on a 
tool whose primary focus is something else. My favorite misfeature is the 
"expand and unexpand linked packages" thingy, and the associated hiding of 
merge conflicts when a source package changes. That's not fun to debug, and 
it won't ever happen with plain git because git comes with excellent 
support for merges. That support is a result of many years of extremely 
heavy use of git by a ton of developers. I don't expect Facebook to be able 
to cope with *that* regardless of their engineering size, and therefore I 
expect that `arc` will fail when people use it for non-obvious stuff.

I suppose most of our developers are either already familiar with git, or 
they have to learn it anyhow to be able to participate in our community in 
an efficient manner. Introducing another patch manager to the mix doesn't 
help, IMHO. This is just to illustrate my experience with tools that 
behave-quite-like-a-SCM but do not actually implement full SCM 
functionality. It works well for quick demos, but it sucks when you start 
using them seriously.

I would encourage anyone who evaluates these tools to pay attention to 
these not-so-obvious usage issues. Having a CLI tool that can fetch a patch 
and apply it to a local checkout is not equivalent to native git refs. It's 
an important building block, but not a finished tool.

I know that I won't be in a business of building these tools. I'm quite 
happy with having them out-of-box with Gerrit.

Cheers,
Jan

-- 
Trojit√°, a fast Qt IMAP e-mail client -- http://trojita.flaska.net/




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