Introduce luci-go components version metric.

Introduce luci-go components version metric.

A large chunk of luci-go library is used as a common GAE runtime for many LUCI
and Chrome Infra apps. It becomes hard to track what apps are outdated and need
to be redeployed.

This CL makes each individual GAE process report 'luci/components/version'
metric with semantic version of the luci-go GAE library, so we can precisely see
what is currently running in production.

The code is a bit more general to eventually allow reporting versions of other
optional components (like Tumble and pRPC server runtime).

R=iannucci@chromium.org, dnj@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2870293002
Committed: https://github.com/luci/luci-go/commit/842c196920ca287e07fdc52378a812b306870776

[Vadim Sh., 2017-05-10 01:05:08]

PTAL

[Vadim Sh., 2017-05-10 01:11:20]

Note that in theory we could extract this information for GAE app version
string, but:
1. It is considerably harder to convert GAE version string of an infra.git GAE
app to a luci-go revision, since we need to be aware of DEPS rolls.
2. I'm pretty sure people neglect to run 'gclient sync' before deploying and
sometimes the version of deployed luci-go doesn't match what's in DEPS at all.

So I figured reporting just a manually updated semantic version is both simpler
and more correct than trying to extract this stuff from GAE version string (or
anything else generated during deployment...).

It's not bulletproof (people would need to remember to bump the version), but
better than nothing.

I've been using similar approach with luci-py's components.auth for a long time,
and it was very helpful. See 'Auth API' column in
https://chrome-infra-auth.appspot.com/auth/services

[iannucci, 2017-05-10 01:13:38]

lgtm! Step 1, get data :)

[Vadim Sh., 2017-05-24 00:57:29]

finally deployed for real and confirmed it works: http://shortn/_6Jh0HidBCp

[Vadim Sh., 2017-05-24 00:57:54]

The CQ bit was checked by vadimsh@chromium.org

[commit-bot: I haz the power, 2017-05-24 00:58:00]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-24 01:06:49]

CQ is committing da patch.

Bot data: {"patchset_id": 20001, "attempt_start_ts": 1495587474228760,
"parent_rev": "2dc055c583df335f62536db98bcffd3afb739795", "commit_rev":
"842c196920ca287e07fdc52378a812b306870776"}

[commit-bot: I haz the power, 2017-05-24 01:06:51]

Description was changed from

==========
Introduce luci-go components version metric.

A large chunk of luci-go library is used as a common GAE runtime for many LUCI
and Chrome Infra apps. It becomes hard to track what apps are outdated and need
to be redeployed.

This CL makes each individual GAE process report 'luci/components/version'
metric with semantic version of the luci-go GAE library, so we can precisely see
what is currently running in production.

The code is a bit more general to eventually allow reporting versions of other
optional components (like Tumble and pRPC server runtime).

R=iannucci@chromium.org, dnj@chromium.org
BUG=
==========

to

==========
Introduce luci-go components version metric.

A large chunk of luci-go library is used as a common GAE runtime for many LUCI
and Chrome Infra apps. It becomes hard to track what apps are outdated and need
to be redeployed.

This CL makes each individual GAE process report 'luci/components/version'
metric with semantic version of the luci-go GAE library, so we can precisely see
what is currently running in production.

The code is a bit more general to eventually allow reporting versions of other
optional components (like Tumble and pRPC server runtime).

R=iannucci@chromium.org, dnj@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2870293002
Committed:
https://github.com/luci/luci-go/commit/842c196920ca287e07fdc52378a812b306870776
==========

[commit-bot: I haz the power, 2017-05-24 01:06:52]

Committed patchset #2 (id:20001) as
https://github.com/luci/luci-go/commit/842c196920ca287e07fdc52378a812b306870776