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amazon-image: fetch metadata only in stage-2

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This also removes automatic enablement/mounting of instance store swap
devices and ext3 filesystems. This behaviour is strongly opinionated
and shouldn't be enabled by default.

The unionfs behaviour never took effect anyway, because the AMI
manifest path only exists for instance store-backed AMIs, which have
not been supported by nixpkgs since
84742e2293 (2019).
This commit is contained in:
Linus Heckemann 2022-11-14 18:19:29 +01:00
parent 24e33a4d2e
commit eddfcf8622
4 changed files with 54 additions and 71 deletions
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36
nixos/doc/manual/from_md/release-notes/rl-2305.section.xml
View File

@ -30,7 +30,7 @@
</section>
<section xml:id="sec-release-23.05-incompatibilities">
<title>Backward Incompatibilities</title>
<itemizedlist spacing="compact">
<itemizedlist>
<listitem>
<para>
<literal>carnix</literal> and <literal>cratesIO</literal> has
@ -42,6 +42,40 @@
instead.
</para>
</listitem>
<listitem>
<para>
The EC2 image module no longer fetches instance metadata in
stage-1. This results in a significantly smaller initramfs,
since network drivers no longer need to be included, and
faster boots, since metadata fetching can happen in parallel
with startup of other services. This breaks services which
rely on metadata being present by the time stage-2 is entered.
Anything which reads EC2 metadata from
<literal>/etc/ec2-metadata</literal> should now have an
<literal>after</literal> dependency on
<literal>fetch-ec2-metadata.service</literal>
</para>
</listitem>
<listitem>
<para>
The EC2 image module previously detected and automatically
mounted ext3-formatted instance store devices and partitions
in stage-1 (initramfs), storing <literal>/tmp</literal> on the
first discovered device. This behaviour, which only catered to
very specific use cases and could not be disabled, has been
removed. Users relying on this should provide their own
implementation, and probably use ext4 and perform the mount in
stage-2.
</para>
</listitem>
<listitem>
<para>
The EC2 image module previously detected and activated
swap-formatted instance store devices and partitions in
stage-1 (initramfs). This behaviour has been removed. Users
relying on this should provide their own implementation.
</para>
</listitem>
</itemizedlist>
</section>
<section xml:id="sec-release-23.05-notable-changes">

7
nixos/doc/manual/release-notes/rl-2305.section.md
View File

@ -22,6 +22,13 @@ In addition to numerous new and upgraded packages, this release has the followin
- `carnix` and `cratesIO` has been removed due to being unmaintained, use alternatives such as [naersk](https://github.com/nix-community/naersk) and [crate2nix](https://github.com/kolloch/crate2nix) instead.
- The EC2 image module no longer fetches instance metadata in stage-1. This results in a significantly smaller initramfs, since network drivers no longer need to be included, and faster boots, since metadata fetching can happen in parallel with startup of other services.
This breaks services which rely on metadata being present by the time stage-2 is entered. Anything which reads EC2 metadata from `/etc/ec2-metadata` should now have an `after` dependency on `fetch-ec2-metadata.service`
- The EC2 image module previously detected and automatically mounted ext3-formatted instance store devices and partitions in stage-1 (initramfs), storing `/tmp` on the first discovered device. This behaviour, which only catered to very specific use cases and could not be disabled, has been removed. Users relying on this should provide their own implementation, and probably use ext4 and perform the mount in stage-2.
- The EC2 image module previously detected and activated swap-formatted instance store devices and partitions in stage-1 (initramfs). This behaviour has been removed. Users relying on this should provide their own implementation.
## Other Notable Changes {#sec-release-23.05-notable-changes}
<!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->

81
nixos/modules/virtualisation/amazon-image.nix
View File

@ -10,11 +10,6 @@ with lib;
let
cfg = config.ec2;
metadataFetcher = import ./ec2-metadata-fetcher.nix {
inherit (pkgs) curl;
targetRoot = "$targetRoot/";
wgetExtraOptions = "-q";
};
in
{
@ -58,8 +53,8 @@ in
boot.extraModulePackages = [
config.boot.kernelPackages.ena
];
boot.initrd.kernelModules = [ "xen-blkfront" "xen-netfront" ];
boot.initrd.availableKernelModules = [ "ixgbevf" "ena" "nvme" ];
boot.initrd.kernelModules = [ "xen-blkfront" ];
boot.initrd.availableKernelModules = [ "nvme" ];
boot.kernelParams = [ "console=ttyS0,115200n8" "random.trust_cpu=on" ];
# Prevent the nouveau kernel module from being loaded, as it
@ -78,67 +73,15 @@ in
terminal_input console serial
'';
boot.initrd.network.enable = true;
# Mount all formatted ephemeral disks and activate all swap devices.
# We cannot do this with the ‘fileSystems’ and ‘swapDevices’ options
# because the set of devices is dependent on the instance type
# (e.g. "m1.small" has one ephemeral filesystem and one swap device,
# while "m1.large" has two ephemeral filesystems and no swap
# devices). Also, put /tmp and /var on /disk0, since it has a lot
# more space than the root device. Similarly, "move" /nix to /disk0
# by layering a unionfs-fuse mount on top of it so we have a lot more space for
# Nix operations.
boot.initrd.postMountCommands =
''
${metadataFetcher}
diskNr=0
diskForUnionfs=
for device in /dev/xvd[abcde]*; do
if [ "$device" = /dev/xvda -o "$device" = /dev/xvda1 ]; then continue; fi
fsType=$(blkid -o value -s TYPE "$device" || true)
if [ "$fsType" = swap ]; then
echo "activating swap device $device..."
swapon "$device" || true
elif [ "$fsType" = ext3 ]; then
mp="/disk$diskNr"
diskNr=$((diskNr + 1))
if mountFS "$device" "$mp" "" ext3; then
if [ -z "$diskForUnionfs" ]; then diskForUnionfs="$mp"; fi
fi
else
echo "skipping unknown device type $device"
fi
done
if [ -n "$diskForUnionfs" ]; then
mkdir -m 755 -p $targetRoot/$diskForUnionfs/root
mkdir -m 1777 -p $targetRoot/$diskForUnionfs/root/tmp $targetRoot/tmp
mount --bind $targetRoot/$diskForUnionfs/root/tmp $targetRoot/tmp
if [ "$(cat "$metaDir/ami-manifest-path")" != "(unknown)" ]; then
mkdir -m 755 -p $targetRoot/$diskForUnionfs/root/var $targetRoot/var
mount --bind $targetRoot/$diskForUnionfs/root/var $targetRoot/var
mkdir -p /unionfs-chroot/ro-nix
mount --rbind $targetRoot/nix /unionfs-chroot/ro-nix
mkdir -m 755 -p $targetRoot/$diskForUnionfs/root/nix
mkdir -p /unionfs-chroot/rw-nix
mount --rbind $targetRoot/$diskForUnionfs/root/nix /unionfs-chroot/rw-nix
unionfs -o allow_other,cow,nonempty,chroot=/unionfs-chroot,max_files=32768 /rw-nix=RW:/ro-nix=RO $targetRoot/nix
fi
fi
'';
boot.initrd.extraUtilsCommands =
''
# We need swapon in the initrd.
copy_bin_and_libs ${pkgs.util-linux}/sbin/swapon
'';
systemd.services.fetch-ec2-metadata = {
wantedBy = [ "multi-user.target" ];
path = [ pkgs.wget ];
script = pkgs.callPackage ./ec2-metadata-fetcher.nix {
targetRoot = "/";
wgetExtraOptions = "";
};
serviceConfig.Type = "oneshot";
};
# Allow root logins only using the SSH key that the user specified
# at instance creation time.
@ -157,8 +100,6 @@ in
# Always include cryptsetup so that Charon can use it.
environment.systemPackages = [ pkgs.cryptsetup ];
boot.initrd.supportedFilesystems = [ "unionfs-fuse" ];
# EC2 has its own NTP server provided by the hypervisor
networking.timeServers = [ "169.254.169.123" ];

1
nixos/modules/virtualisation/ec2-data.nix
View File

@ -18,6 +18,7 @@ with lib;
wantedBy = [ "multi-user.target" "sshd.service" ];
before = [ "sshd.service" ];
after = ["fetch-ec2-metadata.service"];
path = [ pkgs.iproute2 ];