[rack] add request queuing option to the Rack middleware #272

palazzem · 2017-12-12T16:00:52Z

Overview

Provides the request queuing time from the Rack middleware if a frontend web server or load balancer sets a specific header. This is considered an experimental feature and may have breaking changes in the future.

Usage

your web server should set the x-request-start header
your Rack integration should be configured with the following options

Datadog.configure do |c|
  # web_service_name is optional and has `web-server` as default
  c.use :rack, request_queuing: true, web_service_name: 'nginx'
end

Supported format

At the time of writing, only nginx headers are supported in the format of t=1512379167.574.

palazzem · 2017-12-12T16:02:54Z

lib/ddtrace/contrib/rack/request_queue.rb

+          header = env[REQUEST_START]
+
+          if header
+            # nginx header is in the format "t=1512379167.574"


for the current testing phase, only nginx is required; I'll iterate over other formats if they're different.

p-lambert

Looks good to me! Left some comments about code style, but the changes are not necessary, so feel free to skip them!

p-lambert · 2017-12-12T17:11:37Z

lib/ddtrace/contrib/rack/request_queue.rb

+            request_start = Time.at(time_string.to_f)
+            request_start.utc > now ? nil : request_start
+          end
+        rescue StandardError


In ruby you can omit the exception class when it is StandardError

p-lambert · 2017-12-12T17:13:36Z

lib/ddtrace/contrib/rack/request_queue.rb

+        def get_request_start(env, now = Time.now.utc)
+          header = env[REQUEST_START]
+
+          if header


I usually prefer early returns than code nested in conditional branches, but that's only a matter of personal style :)

p-lambert · 2017-12-12T17:14:47Z

lib/ddtrace/contrib/rack/middlewares.rb

@@ -32,19 +40,34 @@ def initialize(app, options = {})
          @app = app
        end

+        def compute_queueing_time(env, tracer)
+          if Datadog.configuration[:rack][:request_queuing]


Same here about the early return comment

delner · 2018-02-01T19:48:19Z

Is this stable enough to merge? Would be cool to close this out if we're happy with it.

LotharSee · 2018-02-02T12:51:23Z

lib/ddtrace/contrib/rack/middlewares.rb

+
+          Datadog::Tracer.log.debug('[experimental] creating request.enqueuing span')
+          tracer.trace(
+            'request.enqueuing',


Nit: the name doesn't align with our usual informal conventions (request. looks like it comes from request library).
I also guess it has to stay generic between web servers (not Nginx only).
So maybe something like web_server.start_request, http_server.start_request?
I also saw that there is a potential for another X-Queue-Start timing, it would then easily translate into a whatever.queue_start?

totally agree, we can change that value with one you've suggested!

If there's an HTTP header named X-Queue-Start, those usually get tagged as http. I'd suggest adding http, like http.queue_start, http.headers.queue_start or something similar (to indicate its origins)

LotharSee · 2018-02-02T12:57:00Z

docs/GettingStarted.md

+
+    Datadog.configure do |c|
+      # web_service_name defaults to `web-server` and is different from Rack `service_name`
+      c.use :rack, request_queuing: true, web_service_name: nginx


Nit: request_queuing is a specific mechanism of the front web server, while here we want to more generally integrate with front web servers. Maybe we could have an option key more generic? Examples: instrument_web|http_server, behind_web_server, http_server_enabled, ...
I guess it also depends on what we will want to do once stable (enabled by default?).

For the option name, yes we can stay more generic. For the future (once it's stable), we can keep it enabled by default so to activate it is enough to change something in the proxy configuration (nginx, HAProxy, whatever).

palazzem · 2018-04-05T16:04:11Z

Rescheduled for 0.13.0 but will be available in a beta release right after the 0.12.0 release.

…ty only for nginx

delner · 2018-04-13T19:29:12Z

lib/ddtrace/contrib/rack/request_queue.rb

+
+        module_function
+
+        def get_request_start(env, now = Time.now.utc)


Consider moving this to the core library in a future pull request. The behavior here is generic enough, and useful for other integrations.

delner

👍

palazzem added do-not-merge/WIP Not ready for merge integrations Involves tracing integrations labels Dec 12, 2017

palazzem requested a review from p-lambert December 12, 2017 16:00

palazzem commented Dec 12, 2017

View reviewed changes

p-lambert previously approved these changes Dec 12, 2017

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palazzem added this to the 0.11.0 milestone Dec 14, 2017

palazzem force-pushed the palazzem/rack-context branch from e9f3fc1 to 12ca7bc Compare December 14, 2017 10:27

palazzem changed the base branch from palazzem/rack-context to master December 14, 2017 13:58

palazzem dismissed p-lambert’s stale review via d81a371 December 14, 2017 14:04

palazzem force-pushed the palazzem/request-queuing branch 2 times, most recently from d81a371 to 9980106 Compare December 14, 2017 14:11

palazzem removed this from the 0.11.0 milestone Jan 11, 2018

delner added this to the 0.11.1 milestone Jan 16, 2018

palazzem modified the milestones: 0.11.1, 0.11.2 Jan 24, 2018

LotharSee reviewed Feb 2, 2018

View reviewed changes

palazzem modified the milestones: 0.11.2, 0.11.3 Feb 2, 2018

delner modified the milestones: 0.11.3, 0.12.0 Feb 5, 2018

delner changed the base branch from master to 0.12-dev February 5, 2018 19:01

delner added the feature Involves a product feature label Feb 5, 2018

palazzem modified the milestones: 0.12.0, 0.13.0 Apr 5, 2018

delner changed the base branch from 0.12-dev to 0.13-dev April 13, 2018 17:33

Emanuele Palazzetti added 2 commits April 13, 2018 14:04

[rack] add request queuing option to the Rack middleware; compatibili…

635874d

…ty only for nginx

[rack] provide request queue documentation

50d75d2

Emanuele Palazzetti and others added 2 commits April 13, 2018 14:37

[wip] add debug logs

275d5f9

Support alternative header X-Queue-Start

9f57afe

delner force-pushed the palazzem/request-queuing branch from 29c7c2a to 9f57afe Compare April 13, 2018 19:00

Changed: 'enqueuing' --> 'queuing' in Rack.

a5d3dfd

delner removed the do-not-merge/WIP Not ready for merge label Apr 13, 2018

delner reviewed Apr 13, 2018

View reviewed changes

delner approved these changes Apr 13, 2018

View reviewed changes

delner merged commit 026da76 into 0.13-dev Apr 13, 2018

palazzem deleted the palazzem/request-queuing branch April 13, 2018 21:21

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[rack] add request queuing option to the Rack middleware #272

[rack] add request queuing option to the Rack middleware #272

palazzem commented Dec 12, 2017 •

edited

palazzem Dec 12, 2017

p-lambert left a comment

p-lambert Dec 12, 2017

palazzem Dec 14, 2017

p-lambert Dec 12, 2017

palazzem Dec 14, 2017

p-lambert Dec 12, 2017

palazzem Dec 14, 2017

delner commented Feb 1, 2018

LotharSee Feb 2, 2018

palazzem Feb 2, 2018

delner Feb 2, 2018

LotharSee Feb 2, 2018

palazzem Feb 2, 2018

palazzem commented Apr 5, 2018

delner Apr 13, 2018

delner left a comment


		module_function

		def get_request_start(env, now = Time.now.utc)

[rack] add request queuing option to the Rack middleware #272

[rack] add request queuing option to the Rack middleware #272

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palazzem commented Dec 12, 2017 • edited

Overview

Usage

Supported format

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delner commented Feb 1, 2018

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palazzem commented Apr 5, 2018

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palazzem commented Dec 12, 2017 •

edited