Improve the retry attempts, error conditions, and IPv6 attempts for fetching ec2 metadata from IMDS

[hjkatz]

Description of changes

Why: NixOS/amis#137

Things done

• Add ipv6 awareness to the script
• Add additional retry options to all curl commands
• Add exit conditions for failures during boot

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[arianvp]

This will add a 10 second delay to booting machines in an IPv6 subnet. I don't think that is desirable.

I think we need to rethink this script instead of patching this in. This is getting very complex

[hjkatz]

Agreed. While implementing this I think there should be a separate trigger or method for identifying which connectivity is preferred, then use that connectivity explicitly.

I'm curious if there's a way we could query the interfaces attached and see if any ipv6 address is available, if so, then we try that first.

But I still think it's odd that dhcp grants ipv6 before ipv4...

What ideas do you have for this script? I'm happy to help implement

[arianvp]

But I still think it's odd that dhcp grants ipv6 before ipv4...

It's just a race condition. Sometimes you get the IPv4 lease sometimes the IPv6 lease first

[hjkatz]

The script could try ipv4/6 back and forth until it finds a working token rather than trying all at once. i.e. we move the retry logic out of curl's opts and into the bash function.