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Oliver Schmidt e362fe9c6d security/acme: limit concurrent certificate generations
fixes #232505

Implements the new option `security.acme.maxConcurrentRenewals` to limit
the number of certificate generation (or renewal) jobs that can run in
parallel. This avoids overloading the system resources with many
certificates or running into acme registry rate limits and network
timeouts.

Architecture considerations:
- simplicity, lightweight: Concerns have been voiced about making this
  already rather complex module even more convoluted. Additionally,
  locking solutions shall not significantly increase performance and
  footprint of individual job runs.
  To accomodate these concerns, this solution is implemented purely in
  Nix, bash, and using the light-weight `flock` util. To reduce
  complexity, jobs are already assigned their lockfile slot at system
  build time instead of dynamic locking and retrying. This comes at the
  cost of not always maxing out the permitted concurrency at runtime.
- no stale locks: Limiting concurrency via locking mechanism is usually
  approached with semaphores. Unfortunately, both SysV as well as
  POSIX-Semaphores are *not* released when the process currently locking
  them is SIGKILLed. This poses the danger of stale locks staying around
  and certificate renewal being blocked from running altogether.
  `flock` locks though are released when the process holding the file
  descriptor of the lock file is KILLed or terminated.
- lockfile generation: Lock files could either be created at build time
  in the Nix store or at script runtime in a idempotent manner.
  While the latter would be simpler to achieve, we might exceed the number
  of permitted concurrent runs during a system switch: Already running
  jobs are still locked on the existing lock files, while jobs started
  after the system switch will acquire locks on freshly created files,
  not being blocked by the still running services.
  For this reason, locks are generated and managed at runtime in the
  shared state directory `/var/lib/locks/`.

nixos/security/acme: move locks to /run

also, move over permission and directory management to systemd-tmpfiles

nixos/security/acme: fix some linter remarks in my code

there are some remarks left for existing code, not touching that

nixos/security/acme: redesign script locking flow

- get rid of subshell
- provide function for wrapping scripts in a locked environment

nixos/acme: improve visibility of blocking on locks

nixos/acme: add smoke test for concurrency limitation

heavily inspired by m1cr0man

nixos/acme: release notes entry on new concurrency limits

nixos/acme: cleanup, clarifications
2023-09-09 20:13:18 +02:00
.github Merge pull request #253621 from tweag/minor-contrib-docs-improvements 2023-09-07 05:21:59 +02:00
doc doc/hooks/zig.section.md: reword 2023-09-09 15:27:11 +00:00
lib nixpkgs/systems: Add ucrt64 as MinGW libc 2023-09-08 10:56:08 +00:00
maintainers Merge pull request #252917 from dunxen/add-liana-package 2023-09-09 11:55:38 +02:00
nixos security/acme: limit concurrent certificate generations 2023-09-09 20:13:18 +02:00
pkgs obs-studio: add flag for decklink support 2023-09-09 19:45:50 +02:00
.editorconfig lib.toPlist: keep test output in external files for their tab indents 2023-03-27 19:25:52 +02:00
.git-blame-ignore-revs git-blame-ignore-revs: add large docs migrations 2023-07-03 02:28:08 +02:00
.gitattributes .gitattributes: fix typo 2023-05-01 12:30:00 +02:00
.gitignore gitignore: Add symlinks produced by :bl in repl 2023-08-04 02:29:48 +03:00
.mailmap
.version 23.11 is Tapir 2023-05-22 21:16:04 +02:00
CONTRIBUTING.md CONTRIBUTING.md: Reword changes acceptable for backport 2023-09-06 20:12:50 +02:00
COPYING
default.nix
flake.nix nixosModules.pkgsReadOnly: init 2023-05-10 15:55:09 +02:00
README.md README.md: Rough move to new contribution doc files 2023-08-13 21:54:50 +02:00

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