doc && http: fix agent default value for keepAlive

[zckrs]

Since node 19, option keepAlive is true by default.

[nodejs-github-bot]

Review requested:

• @nodejs/http
• @nodejs/net

[lpinca]

node/lib/_http_agent.js

Line 111 in 99f6084

this.keepAlive = this.options.keepAlive || false;

The default value is false.

[zckrs]

🤔

So a another line in doc is misleading.

https://github.com/nodejs/node/pull/51115/files#diff-d692ac4524379ec6a1201165e8ff8d3267c8130e07014e8221ebf7e6f80c6641R183-R184

Because

node/lib/_http_agent.js

Line 557 in 99f6084

globalAgent: new Agent({ keepAlive: true, scheduling: 'lifo', timeout: 5000 }),

I understand the default value for a new Agent is falsy keepAlive, but the "default" globalAgent is set to true.

~ » nvm use system
Now using system version of node: v20.10.0 (npm v10.2.5)
--------------------------------------------------------------------------------------------------
~ » node -pe 'const {keepAlive, keepAliveMsecs} = http.globalAgent; ({keepAlive, keepAliveMsecs})'
{ keepAlive: true, keepAliveMsecs: 1000 }

~ » nvm use 18
Now using node v18.19.0 (npm v10.2.3)
--------------------------------------------------------------------------------------------------
~ » node -pe 'const {keepAlive, keepAliveMsecs} = http.globalAgent; ({keepAlive, keepAliveMsecs})'
{ keepAlive: false, keepAliveMsecs: 1000 }

---

To be complete, in our organization (https://www.radiofrance.fr/) we had some surprises with this change in our kubernetes infrastructure.

[ShogunPanda]

Yes, you are right: the misleading line is the one you linked above. In #43522 I changed some options for the default agent (while leaving the constructor behavior untouched).
Could you please update this PR to fix that offending line instead of the one you proposed?

[zckrs]

Done. I hope my changes are what you expect.

[lpinca]

I don't think we should change the default value in the constructor. The global agent has uses a different value and that's ok. Anyway this PR is correct now so I'm dropping my request for changes.

Changes are correct now

[mcollina]

Why is this semver-major?

[lpinca]

Why is this semver-major?

It changes the default value of the keepAlive option in the http.Agent constructor from false to true.

[ShogunPanda]

I agree, if we want the PR this way. But I don't think we want to flip the value on the code, just in the docs for the default agent (note: not the constructor, the default instance).