nixosTests: share IMDSv2 server across EC2 test infrastructure

- Extract imds-server derivation into common/imds-server.nix so both
  ec2-image.nix and common/ec2.nix share the same definition.

- Update common/ec2.nix (makeEc2Test) to use the IMDSv2 server
  instead of micro_httpd, and add token/instance-id to the metadata
  directory so the full IMDSv2 flow works.

- Simplify ec2-image.nix to import from the shared definition.

nixos/tests/common/ec2.nix

@@ -2,7 +2,12 @@
 
 with pkgs.lib;
 
+let
+  imdsServer = import ./imds-server.nix { inherit pkgs; };
+in
 {
+  inherit imdsServer;
+
   makeEc2Test =
     {
       name,
@@ -18,9 +23,12 @@ with pkgs.lib;
         name = "metadata";
         buildCommand = ''
           mkdir -p $out/1.0/meta-data
+          mkdir -p $out/latest/api
           ln -s ${pkgs.writeText "userData" userData} $out/1.0/user-data
           echo "${hostname}" > $out/1.0/meta-data/hostname
           echo "(unknown)" > $out/1.0/meta-data/ami-manifest-path
+          echo "i-1234567890abcdef0" > $out/1.0/meta-data/instance-id
+          echo "test-imdsv2-token" > $out/latest/api/token
         ''
         + optionalString (sshPublicKey != null) ''
           mkdir -p $out/1.0/meta-data/public-keys/0
@@ -67,7 +75,7 @@ with pkgs.lib;
         start_command = (
             "qemu-kvm -m 1024"
             + " -device virtio-net-pci,netdev=vlan0"
-            + " -netdev 'user,id=vlan0,net=169.0.0.0/8,guestfwd=tcp:169.254.169.254:80-cmd:${pkgs.micro-httpd}/bin/micro_httpd ${metaData}'"
+            + " -netdev 'user,id=vlan0,net=169.0.0.0/8,guestfwd=tcp:169.254.169.254:80-cmd:${getExe imdsServer} ${metaData}'"
             + f" -drive file={disk_image},if=virtio,werror=report"
             + " $QEMU_OPTS"
         )

nixos/tests/common/imds-server.nix

@@ -0,0 +1,4 @@
+# Minimal IMDSv2-compatible metadata server for NixOS EC2 tests.
+# Runs in inetd mode (stdin/stdout), drop-in for micro_httpd in
+# QEMU guestfwd and socat contexts.
+{ pkgs }: pkgs.writers.writePython3Bin "imds-server" { } (builtins.readFile ./imds-server.py)

nixos/tests/ec2-image.nix

@@ -13,10 +13,7 @@ let
   inherit (lib) mkAfter mkForce;
   pkgs = config.node.pkgs;
 
-  # Minimal IMDSv2-compatible metadata server (inetd-mode, drop-in for micro_httpd)
-  imdsServer = pkgs.writers.writePython3Bin "imds-server" { } (
-    builtins.readFile ./common/imds-server.py
-  );
+  imdsServer = import ./common/imds-server.nix { inherit pkgs; };
 
   # Build an EC2 image configuration
   imageCfg =