IPv6 support

[arianvp]

the AMI does not come up properly with IPv6.

Neither is an IP picked up through DHCPv6 (amazon doesn't do SLAAC) nor does our user data scripts work as they don't go over ipv6LL

[arianvp]

It is strange because the amazon-linux-2023 ami just gets a DHCPv4 lease on 169.xxxx and can reach the IMDS over Ipv4 even in an ipv6-only subnet. I'm not sure what is different about our configuration

[arianvp]

Okay update:

Ipv6 is picked up. However. network-online.target is now racey. It can be that ipv6 is up before ipv4 is and then we fail to fetch from IMDS.

We should fix to networkd to have more control over this

[markwellis]

Any update on this? It's still causing a lot of problems for me. Thanks

[takeda]

Same, ironically today this race condition was happening for me all the time. Not sure what happened, perhaps AWS changed something but in the past this happened maybe like 1 out of 5 and now is 5 out of 5.

[arianvp]

Contributions welcome. I don't have time to look into this soon

My approach would be to edit https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/amazon-image.nix
and

1. Change to networkd networking.useNetworkd = true;
2. Set RequiredFamilyForOnline=ipv4 on systemd.networks.990-ethernet-default-dhcp

build image and see if it fixes. This forces networkd to wait for IPv4 to be up before considering the link "online"

[markwellis]

Thanks i should have time to look into it in 1-2 weeks. I'll send a PR when I do 🙏

…

On Sat, 23 Aug 2025, at 09:49, Arian van Putten wrote: *arianvp* left a comment (NixOS/amis#110) <#110 (comment)> Contributions welcome. I don't have time to look into this soon My approach would be to edit https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/amazon-image.nix and 1. Change to networkd `networking.useNetworkd = true;` 2. Set `RequiredFamilyForOnline=ipv4` on `systemd.networks.990-ethernet-default-dhcp` build image and see if it fixes. This forces networkd to wait for IPv4 to be up before considering the link "online" — Reply to this email directly, view it on GitHub <#110 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABG5WED4AB77MOUOVLNPHY33PAMJTAVCNFSM6AAAAABYGREOFSVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTEMJWGU2DKNJYGM>. You are receiving this because you commented.Message ID: ***@***.***>

[sebastianmarines]

Just leaving my comment here since I'm having issues with IPv6-only subnets. I'm testing a fix to the IDMS issue, and I want to discuss it here since I don't have much experience. There is an IPv6 endpoint accessible in fd00:ec2::254 according to https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/configuring-instance-metadata-service.html.

This script https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/virtualisation/ec2-metadata-fetcher.sh has the IPv4 endpoint hardcoded and I’m thinking that adding a check to see if the IPv6 endpoint is accessible would help.

I will test this during the week, but any other ideas are appreciated.

[arianvp]

network-online.target still needs to be fixed. You might fix just this script but everything else depending on network-online.target will still be broken