Fix installer DNS (#840)

conf/build.manifest

@@ -329,6 +329,8 @@ iso-packages:
 - python3-truenas-installer
 - udhcpc
 - vim-tiny
+# Must be the last package as installing it breaks /etc/resolv.conf in chroot
+- systemd-resolved
 
 #
 # List of Git source repositories the build will checkout and perform a debian

scale_build/image/iso.py

@@ -32,10 +32,18 @@ def install_iso_packages():
 def install_iso_packages_impl():
     run_in_chroot(['apt', 'update'])
 
+    with open(f"{CHROOT_BASEDIR}/etc/resolv.conf") as f:
+        resolv_conf = f.read()
+
     # echo "/dev/disk/by-label/TRUENAS / iso9660 loop 0 0" > ${CHROOT_BASEDIR}/etc/fstab
     for package in get_manifest()['iso-packages']:
         run_in_chroot(['apt', 'install', '-y', package])
 
+    # Installing systemd-resolved breaks existing resolv.conf
+    os.unlink(f"{CHROOT_BASEDIR}/etc/resolv.conf")
+    with open(f"{CHROOT_BASEDIR}/etc/resolv.conf", "w") as f:
+        f.write(resolv_conf)
+
     # Inject vendor name into grub.cfg
     with open(CONF_GRUB, 'r') as f:
         grub_cfg = f.read()
@@ -55,7 +63,7 @@ def make_iso_file():
     run(fr'chroot {CHROOT_BASEDIR} /bin/bash -c "echo -e \"root\nroot\" | passwd root"', shell=True)
 
     # Bring up network for the installer
-    run(f'chroot {CHROOT_BASEDIR} systemctl enable systemd-networkd', shell=True)
+    run(f'chroot {CHROOT_BASEDIR} systemctl enable systemd-networkd systemd-resolved', shell=True)
 
     # Create /etc/version
     with open(os.path.join(CHROOT_BASEDIR, 'etc/version'), 'w') as f: