diskimage-builder/diskimage_builder/elements/simple-init/README.rst
Ian Wienand 97c01e48ed Move elements & lib relative to diskimage_builder package
Currently we have all our elements and library files in a top-level
directory and install them into
<root>/share/diskimage-builder/[elements|lib] (where root is either /
or the root of a virtualenv).

The problem with this is that editable/development installs (pip -e)
do *not* install data_files.  Thus we have no canonical location to
look for elements -- leading to the various odd things we do such as a
whole bunch of guessing at the top of disk-image-create and having a
special test-loader in tests/test_elements.py so we can run python
unit tests on those elements that have it.

data_files is really the wrong thing to use for what are essentially
assets of the program.  data_files install works well for things like
config-files, init.d files or dropping documentation files.

By moving the elements under the diskimage_builder package, we always
know where they are relative to where we import from.  In fact,
pkg_resources has an api for this which we wrap in the new
diskimage_builder/paths.py helper [1].

We use this helper to find the correct path in the couple of places we
need to find the base-elements dir, and for the paths to import the
library shell functions.

Elements such as svc-map and pkg-map include python unit-tests, which
we do not need tests/test_elements.py to special-case load any more.
They just get found automatically by the normal subunit loader.

I have a follow-on change (I69ca3d26fede0506a6353c077c69f735c8d84d28)
to move disk-image-create to a regular python entry-point.

Unfortunately, this has to move to work with setuptools.  You'd think
a symlink under diskimage_builder/[elements|lib] would work, but it
doesn't.

[1] this API handles stuff like getting files out of .zip archive
modules, which we don't do.  Essentially for us it's returning
__file__.

Change-Id: I5e3e3c97f385b1a4ff2031a161a55b231895df5b
2016-11-01 17:27:41 -07:00

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===========
simple-init
===========
Basic network and system configuration that can't be done until boot
Unfortunately, as much as we'd like to bake it in to an image, we can't
know in advance how many network devices will be present, nor if DHCP is
present in the host cloud. Additionally, in environments where cloud-init
is not used, there are a couple of small things, like mounting config-drive
and pulling ssh keys from it, that need to be done at boot time.
Autodetect network interfaces during boot and configure them
------------------------------------------------------------
The rationale for this is that we are likely to require multiple
network interfaces for use cases such as baremetal and there is no way
to know ahead of time which one is which, so we will simply run a
DHCP client on all interfaces with real MAC addresses (except lo) that
are visible on the first boot.
The script `/usr/local/sbin/simple-init.sh` will be called
early in each boot and will scan available network interfaces and
ensure they are configured properly before networking services are started.
Processing startup information from config-drive
------------------------------------------------
On most systems, the DHCP approach desribed above is fine. But in some clouds,
such as Rackspace Public cloud, there is no DHCP. Instead, there is static
network config via `config-drive`. `simple-init` will happily call
`glean` which will do nothing if static network information is
not there.
Finally, glean will handle ssh-keypair-injection from config
drive if cloud-init is not installed.
Chosing glean installation source
---------------------------------
By default glean is installed using pip using the latest release on pypi.
It is also possible to install glean from a specified git repository
location. This is useful for debugging and testing new glean changes
for example. To do this you need to set these variables::
DIB_INSTALLTYPE_simple_init=repo
DIB_REPOLOCATION_glean=/path/to/glean/repo
DIB_REPOREF_glean=name_of_git_ref
For example to test glean change 364516 do::
git clone https://git.openstack.org/openstack-infra/glean /tmp/glean
cd /tmp/glean
git review -d 364516
git checkout -b my-test-ref
Then set your DIB env vars like this before running DIB::
DIB_INSTALLTYPE_simple_init=repo
DIB_REPOLOCATION_glean=/tmp/glean
DIB_REPOREF_glean=my-test-ref