Increase default keepalive_timeout server-side.

[Dreamsorcerer]

As we strongly recommend deploying apps behind a reverse proxy it makes sense to optimise the defaults for this use case.

When using a reverse proxy it's important to have a longer timeout than the proxy's timeout, otherwise we likely hit race conditions with the proxy trying to forward another request as we close the connection.

For proxies, it'd probably make the most sense to actually remove the timeout entirely, but for users without proxies the defaults should still be safe, therefore I'm proposing to just make it substantially longer by default.

I expect the vast majority of proxies to have a keepalive of 1 hour or less, so have chosen a value just over the 1 hour mark (for reference, nginx defaults to 75 seconds, ALB to 1 hour).

See #9138

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.41%. Comparing base (2816002) to head (4145c33).
Report is 1054 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9285      +/-   ##
==========================================
+ Coverage   97.31%   98.41%   +1.10%     
==========================================
  Files         105      107       +2     
  Lines       34759    34828      +69     
  Branches     3351     4132     +781     
==========================================
+ Hits        33825    34277     +452     
+ Misses        692      380     -312     
+ Partials      242      171      -71     

Flag	Coverage Δ
CI-GHA	98.30% <ø> (+0.99%)	⬆️
OS-Linux	97.97% <ø> (?)
OS-Windows	96.37% <ø> (?)
OS-macOS	97.64% <ø> (+0.33%)	⬆️
Py-3.10.11	97.63% <ø> (+0.32%)	⬆️
Py-3.10.15	97.56% <ø> (?)
Py-3.11.10	97.53% <ø> (?)
Py-3.11.9	97.59% <ø> (?)
Py-3.12.6	98.02% <ø> (?)
Py-3.13.0-rc.2	98.00% <ø> (?)
Py-3.9.13	97.53% <ø> (?)
Py-3.9.20	97.46% <ø> (?)
Py-pypy7.3.16	97.08% <ø> (?)
VM-macos	97.64% <ø> (+0.33%)	⬆️
VM-ubuntu	97.97% <ø> (?)
VM-windows	96.37% <ø> (?)

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[bdraco]

This could result in significantly more memory being used on busy systems. Its probably fine though as its easy enough to override, but it may surprise some users.

[Dreamsorcerer]

This could result in significantly more memory being used on busy systems.

Well, a busy system should definitely have a proxy, and this shouldn't have any impact in that situation.

[patchback]

Backport to 3.11: 💔 cherry-picking failed — conflicts found

❌ Failed to cleanly apply de997af on top of patchback/backports/3.11/de997af2069781a7d50639fe59ad9ac8e3e9847e/pr-9285

Backporting merged PR #9285 into master

1. Ensure you have a local repo clone of your fork. Unless you cloned it
   from the upstream, this would be your origin remote.
2. Make sure you have an upstream repo added as a remote too. In these
   instructions you'll refer to it by the name upstream. If you don't
   have it, here's how you can add it:

   $ git remote add upstream https://github.com/aio-libs/aiohttp.git

3. Ensure you have the latest copy of upstream and prepare a branch
   that will hold the backported code:

   $ git fetch upstream
   $ git checkout -b patchback/backports/3.11/de997af2069781a7d50639fe59ad9ac8e3e9847e/pr-9285 upstream/3.11

4. Now, cherry-pick PR Increase default keepalive_timeout server-side. #9285 contents into that branch:

   $ git cherry-pick -x de997af2069781a7d50639fe59ad9ac8e3e9847e

   If it'll yell at you with something like fatal: Commit de997af2069781a7d50639fe59ad9ac8e3e9847e is a merge but no -m option was given., add -m 1 as follows instead:

   $ git cherry-pick -m1 -x de997af2069781a7d50639fe59ad9ac8e3e9847e

5. At this point, you'll probably encounter some merge conflicts. You must
   resolve them in to preserve the patch from PR Increase default keepalive_timeout server-side. #9285 as close to the
   original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/3.11/de997af2069781a7d50639fe59ad9ac8e3e9847e/pr-9285

7. Create a PR, ensure that the CI is green. If it's not — update it so that
   the tests and any other checks pass. This is it!
   Now relax and wait for the maintainers to process your pull request
   when they have some cycles to do reviews. Don't worry — they'll tell you if
   any improvements are necessary when the time comes!

🤖 @patchback
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