sig_cloud/diskimage-builder
2
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Formalise saving of /etc/resolv.conf

Browse Source 
systemd-resolved has a new behaviour in bionic, in that if there is no
/etc/resolv.conf file when it installs, it assumes it is a fresh
system and makes /etc/resolf.conf a symlink into its compatability
files.

dib ends up saving & restoring whatever /etc/resolv.conf we have after
the inital chroot creation, which may not be what we want -- in the
above case it restores the system-resolved symlink.  For
openstack-infra, we use unbound and want simply "127.0.0.1" in a
/etc/resolv.conf file [1].

Formalise the ability to save specific contents into the final image.
Add documentation, and a note in the code that it's an external
interface.

I would have preferred to namespace the .ORIG file with DIB_ or
similar, but this unofficial interface has already escaped into the
wild.  Leave it as is for simplicity.

[1] Note that systemd-resolved will obey /etc/resolv.conf as you would
expect, if file exists.

Change-Id: Ie0e97d8072e2b21a54b053fa6fb07b62960c686d
This commit is contained in:
Ian Wienand 2018-04-03 15:20:42 +10:00
parent 855ab0d850
commit e443700b5c
3 changed files with 39 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
diskimage_builder/lib/common-functions
View File

@ -338,8 +338,11 @@ function create_base () {
fi
# Configure Image
# Setup resolv.conf so we can chroot to install some packages
if [ -L $TMP_MOUNT_PATH/etc/resolv.conf ] || [ -f $TMP_MOUNT_PATH/etc/resolv.conf ] ; then
# Save resolv.conf as created by the initial install. Note the
# .ORIG file is an exported interface -- it may be modified and we
# will copy it back in during finalisation of the image.
if [[ -e $TMP_MOUNT_PATH/etc/resolv.conf ]]; then
sudo mv $TMP_MOUNT_PATH/etc/resolv.conf $TMP_MOUNT_PATH/etc/resolv.conf.ORIG
fi

14
diskimage_builder/lib/img-functions
View File

@ -93,6 +93,13 @@ function run_d_in_target () {
function finalise_base () {
TARGET_ROOT=$TMP_MOUNT_PATH run_d cleanup
# Finalise resolv.conf
#
# NOTE(ianw): the /etc/resolv.conf.ORIG file is an
# external interface; elements might put a resolv.conf they
# want in the final image into this file.
#
# In create_base() we replaced/created the initial resolv.conf
# inside the image with a copy of the "outside" version so that
# resolving during the build will work.
@ -106,13 +113,14 @@ function finalise_base () {
# so remove the old saved file
sudo rm -f $TMP_MOUNT_PATH/etc/resolv.conf.ORIG
else
# Remove the resolv.conf we created above
# Remove the resolv.conf we created and put the original (or
# perhaps modified) version back.
sudo rm -f $TMP_MOUNT_PATH/etc/resolv.conf
# Move the original back
if [ -L $TMP_MOUNT_PATH/etc/resolv.conf.ORIG ] || [ -f $TMP_MOUNT_PATH/etc/resolv.conf.ORIG ] ; then
if [ -e $TMP_MOUNT_PATH/etc/resolv.conf.ORIG ]; then
sudo mv $TMP_MOUNT_PATH/etc/resolv.conf.ORIG $TMP_MOUNT_PATH/etc/resolv.conf
fi
fi
# Cleanup /tmp in the guest, so there is less cruft left there
unmount_dir $TMP_MOUNT_PATH/tmp
find $TMP_MOUNT_PATH/tmp -maxdepth 1 -mindepth 1 | xargs sudo rm -rf --one-file-system

23
doc/source/user_guide/building_an_image.rst
View File

@ -646,6 +646,29 @@ If tmpfs is not used, you will need enough room in /tmp to store two
uncompressed cloud images. If tmpfs is used, you would still need /tmp space
for one uncompressed cloud image and about 20% of that image for working files.
Nameservers
-----------
To ensure elements can access the network, ``disk-image-create``
replaces the ``/etc/resolv.conf`` within the chroot with a copy of the
host's file early in the image creation process.
The final ``/etc/resolv.conf`` can be controlled in a number of ways.
If, during the build, the ``/etc/resolv.conf`` file within the chroot
is replaced with a symlink, this will be retained in the final image
[1]_. If the file is marked immutable, it will also not be touched.
.. [1] This somewhat odd case was added for installation of the
``resolvconf`` package, which replaces ``/etc/resolv.conf``
with a symlink to it's version. Depending on its contents, and
what comes after the installation in the build, this mostly
works.
If you would like specific contents within the final
``/etc/resolv.conf`` you can place them into
``/etc/resolv.conf.ORIG`` during the build. As one of the final
steps, this file will be ``mv`` to ``/etc/resolv.conf``.
Chosing an Architecture
-----------------------