Drop official support for Node.js v5 and v7?

[watson]

There have long been an issue with the latest version of Node.js 7 (v7.10.x) that means we cannot instrument it properly as all net.connect calls uses an internal function call that cannot be patched. This issue was fixed in 8.x, but the fix was never back-ported to the 7.x branch. So we only support up to version 7.9.0 on the 7.x branch.

Currently we have pinned our CI servers to test against Node.js version 7.9.x instead of 7.x, but that's not really a realistic scenario as people who still run version 7 would most likely run the latest version.

So maybe we should consider completely dropping support for version 7 (and 5 while we're at it) so that we don't waste time testing these versions on CI?

For reference, here's the official end-of-life dates for all the major Node.js versions:

Release	Initial Release	LTS Start	Maintenance Start	End-of-Life	EoL Status
v0.10	2013-03-11			2016-10-31
v0.12	2015-02-06			2016-12-31
v4	2015-09-08	2015-10-12	2017-04-01	2018-04-30
v5	2015-10-29		2016-04-30	2016-06-30
v6	2016-04-26	2016-10-18	2018-04-30	2019-04-01
v7	2016-10-25		2017-04-30	2017-06-30
v8	2017-05-30	2017-10-31	Apr 2019	Dec 2019
v9	2017-10-01		Apr 2018	Jun 2018
v10	Apr 2018	Oct 2018	Apr 2020	Apr 2021

[watson]

@roncohen @makwarth @Qard what's your thoughts on this?

[Qard]

Yeah, I think it's reasonable following the deprecation cycle of Node.js itself, supporting only LTS releases long-term.

[roncohen]

Sounds good to me 👍

[makwarth]

SGTM (following the LTS schedule)

[watson]

It's settled then 😃 Let's make sure this happens before GA, as it's a breaking change.

[Qard]

I would also suggest communicating that we officially follow the same deprecation cycle as Node.js core. That way it's clear beforehand when support for a given version will be dropped.

[Qard]

Also, given that dropping 4 was not suggested, I assume we are timing with EOL and not maintenance mode? Would there be any difference to our support to parallel the reduced support of maintenance mode in Node.js core?

[Qard]

I've dropped 5 and 7 from the test matrix in #169. What else do we need to do to close this issue? Docs changes, I assume? Anything else?

[watson]

Yeah, I think we should support all Node.js versions that are in maintenance mode as well (i.e. also v4). I don't think we should differentiate in our level of support for active vs LTS vs maintenance mode. A lot of companies run Node.js versions in maintenance mode for production applications and it's perfectly safe to do so.

#168 looks fine. We'll also need to update the compatibly section of our docs and the engine field:

apm-agent-nodejs/package.json

Lines 29 to 31 in 277d462

	"engines": {
	"node": ">=4.0.0"
	},