Add docs on structured logging in GitLab

In GitLab 9.5, we have added structured logging via Lograge. This MR adds documentation about where to find the files and how to interpret the information.

changed milestone to %9.5

added Pick into Stable label

FYI structured logging fans: @pcarranza, @briann, @victorcete, @andrewn, @smcgivern, @sitschner. I think these logs will automatically be picked up by our logging infrastructure and parsed properly as JSON, but somebody should double check. They are already available on dev if you want to verify.

Hmm, it doesn't appear that any of the Grape API endpoints are being logged in this file. I suppose it doesn't appear as a typical controller request.

@stanhu Awesome news!

Currently we only parse JSON messages for type=gitlab logs, so as long as it's being delivered via rsyslogd to /gitlab-log/*/*gitlab.log on the logstash boxes, it should be fine:

Configuration is here:

https://gitlab.com/gitlab-cookbooks/gitlab-elk/blob/master/templates/default/logstash-gitlab.erb#L134

From a quick glance, everything looks like it'll work.

Basically anything coming from the Rails log shipper arrives as type=gitlab.

mentioned in issue #36189 (closed)

added 6 commits

• a4ced528...acd270ae - 5 commits from branch master
• 07ddbbb4 - Add docs on structured logging in GitLab

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@briann @andrewn Thanks for confirming.

approved this merge request

merged

mentioned in commit 358a07cf

@stanhu amazing! Is there an issue about adding the ability for developers to do that? I have a couple of places where I'd want to (typically when I'm shelling out to git, which will go away eventually anyway, but for now it would be really useful).

@smcgivern See https://gitlab.com/gitlab-org/gitlab-ce/issues/35388. I recommend that we deprecate Rails.logger calls there. For Geo, we're using structured logging now, and we could follow a similar approach for other parts of the system (e.g. Sidekiq): https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2482

Picked into 9-5-stable, will go into 9.5.0 RC2.

removed Pick into Stable label

mentioned in commit 0ca8375c