Send trace context with logs from web applications

[liyanhui1228]

For #3359. This feature add the trace_id to GAE app logs and enables the logs correlation based on the trace_id.

For flask the trace_id is extracted from request headers, for django I used a middleware to store the request in thread local, and then get the trace_id from it. The user will need to add the middleware to django settings before deploy the app. Will add the unit test later.

[dhermes]

@liyanhui1228 Do you plan on updating system tests in this PR? If "no", a branch from your own fork is preferred over a branch in the main repository. No need to change it on this one (it isn't really a big deal) but something to think of for future PRs.

[liyanhui1228]

@dhermes Yeah system test seems necessary for this PR, will consider add it. And thanks for the tip, next time I'll use my own fork if not updating system tests.

[waprin]

In Django you need users to specify the middleware in settings.py. So I think you either need a hack to try to inject it at runtime, or docs on how Django users are expected to install it.

Also Django changes reasonably quickly, so you're going to want to decide which versions you support and decide what to do for versions you don't support (probably fall back to unknown). Check out Django release roadmap. 1.11 is the current default pip package and the LTS version so that's the obvious one, 1.9, 1.10, and 2.0 are currently supported so also nice to have.

Overall direction LGTM, will be OOO later in week until after the holiday so don't block on me to merge.

[liyanhui1228]

@waprin Thanks for your comments! I plan to update the docs to let the user add the middleware to django settings, because I found that it is risky to modify the settings at runtime.

[liyanhui1228]

@dhermes Great! Thanks for fixing it.

[theacodes]

@liyanhui1228 Thank you! :)

[tcroiset]

Hi @liyanhui1228
Can't find doc for that.
Do you have any example of appropriate django settings?

For now, we configure Django with this handler

handlers = {
    'app_engine': {
        'level': 'DEBUG',
        'formatter': 'verbose',
        'class': 'google.cloud.logging.handlers.app_engine.AppEngineHandler',
        'filters': ['request'],
        'client': logging.Client()
    }
}

Is it the suggested way?

[liyanhui1228]

@tcroiset Adding 'google.cloud.logging.handlers.middleware.request.RequestMiddleware', to the MIDDLEWARE_CLASSES section in your settings.py will enable the logging correlation feature for django application.