549 additional application metrics 2

[InoMurko]

📋 Add associated issues, tickets, docs URL here.

Overview

Migration from AppSignal to Datadog with Spandex, Spandex Ecto and Spandex Phoenix with supporting lib VmStats.

Changes

• Removed AppSignal completely
• Support to exclude :rocksdb as dependency, useful for local builds because it taking ages to compile.
• Swapped custom function annotations provided by Appsignal with SpandexDecorators and added example usage pattern for syncing procedure that happens in EthereumEventListener. Will be adding more as we proceed.
• to ensure telemetry handlers are attached they're part of startup procedure https://hexdocs.pm/elixir/Application.html#c:start_phase/3
• Removed Recorder process and introduced telemetry handlers (*...Measure modules - they should be understood as an extension (like Core modules) to the parent process module) for named processes.
• removed increment_metrics_counter functions in controller and will later add them as a Plug.
• moved dependencies that we altered into OmiseGo repo

Testing

No tests removed or features changed so same testing would apply.

[coveralls]

Coverage increased (+0.5%) to 85.026% when pulling cc192f9 on 549-Additional_application_metrics_2 into 117d556 on master.

[InoMurko]

Some of the things we're able to gather now via APM.

[chrishunt]

This is great @InoMurko! Dropped a few comments.

[pdobacz]

LGTM, just a couple of non-blocking comments added

[pdobacz]

can we call this outside of .Core so that it remains side-effect free?

[InoMurko]

hm... what causes the side effect?

[pdobacz]

Isn't talking to :telemetry one?

Sorry if I'm having false assumptions here, but I'm guessing this talks to some dependency to do sth. .Core.xyz functions are written with the intent of remaining pure.

Unless absolutely necessary we avoid doing calling external stuff in .Core.xyz, I think the only exception was made for _ = Logger... calls, but only in a few cases.

events and state are available outside, so the move seems to be an easy one.

[InoMurko]

This event gets forwarded to the dedicated Ethereum event listener handler located in module OMG.EthereumEventListener.Measure

I don't quite understand what you mean by side effect though indeed the change isn't big, but would like to understand where keeping .Core.xyz pure comes from.

[pdobacz]

would like to understand where keeping .Core.xyz pure comes from.

Sure thing! It comes from the approach adopted, so segregate logic into such Core modules, with no side effects/side causes. These modules would hold pure functions (same output for same input etc.). Then they can be robustly/quickly tested in unit tests and also I think they are easier to reason about, in general, being just these reliable chunks of logic.

[InoMurko]

A previous commit removes logging and replaces it with datadog trace
dbcd522#diff-5fcd99569a2ce28c62745940476ced06R233

looks liek this:

[chrishunt]

🚀