Merge "Prettify 'Developing Elements' documentation"
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@ -6,8 +6,13 @@ Developing Elements
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Conform to the following conventions:
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* Use the environment for overridable defaults, prefixing environment variable
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names with "DIB\_". For example: DIB\_MYDEFAULT=${DIB\_MYDEFAULT:-default}
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If you do not use the DIB\_ prefix you may find that your overrides are
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names with ``DIB_``. For example:
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.. sourcecode:: sh
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DIB_MYDEFAULT=${DIB_MYDEFAULT:-default}
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If you do not use the ``DIB`` prefix you may find that your overrides are
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discarded as the build environment is sanitised.
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* Consider that your element co-exists with many others and try to guard
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@ -15,27 +20,29 @@ Conform to the following conventions:
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* Two elements use the source-repositories element, but use the same filename
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for the source-repositories config file. Files such as these (and indeed the
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scripts in the various .d directories listed below) should be named such
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that they are unique. If they are not unique, when the combined tree is
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created by disk-image-builder for injecting into the build environment, one
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of the files will be overwritten.
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scripts in the various .d directories :ref:`listed below
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<phase-subdirectories>`) should be named such that they are unique. If they
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are not unique, when the combined tree is created by disk-image-builder for
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injecting into the build environment, one of the files will be overwritten.
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* Two elements copy different scripts into /usr/local/bin with the same name.
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If they both use set -e and cp -n then the conflict will be caught and cause
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the build to fail.
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* Two elements copy different scripts into ``/usr/local/bin`` with the same
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name. If they both use ``set -e`` and ``cp -n`` then the conflict will be
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caught and cause the build to fail.
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* If your element mounts anything into the image build tree ($TMP\_BUILD\_DIR)
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then it will be automatically unmounted when the build tree is unmounted -
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and not remounted into the filesystem image - if the mount point is needed
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again, your element will need to remount it at that point.
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* If your element mounts anything into the image build tree (``$TMP_BUILD_DIR``)
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then it will be automatically unmounted when the build tree is unmounted - and
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not remounted into the filesystem image - if the mount point is needed again,
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your element will need to remount it at that point.
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* If caching is required, elements should use a location under
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$DIB\_IMAGE\_CACHE.
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``$DIB_IMAGE_CACHE``.
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* Elements should allow for remote data to be cached. When
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$DIB\_OFFLINE is set, this cached data should be used if
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possible. See the *Global image-build variables* section of this
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document for more information.
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* Elements should allow for remote data to be cached. When ``$DIB_OFFLINE`` is
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set, this cached data should be used if possible.
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See the :ref:`dev-global-image-build-variables` section of this document for
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more information.
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.. _phase-subdirectories:
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Phase Subdirectories
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^^^^^^^^^^^^^^^^^^^^
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@ -43,12 +50,26 @@ Phase Subdirectories
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Make as many of the following subdirectories as you need, depending on what
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part of the process you need to customise. The subdirectories are executed in
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the order given here. Scripts within the subdirectories should be named with a
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two-digit numeric prefix, and are executed in numeric order. Only files which
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are marked executable (+x) will be run, so other files can be stored in these
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directories if needed. As a convention, we try to only store executable scripts
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in the phase subdirectories and store data files elsewhere in the element.
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two-digit numeric prefix, and are executed in numeric order.
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* root.d: Create or adapt the initial root filesystem content. This is where
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Only files which are marked executable (+x) will be run, so other files can be
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stored in these directories if needed. As a convention, we try to only store
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executable scripts in the phase subdirectories and store data files elsewhere in
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the element.
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The phases are:
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#. ``root.d``
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#. ``extra-data.d``
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#. ``pre-install.d``
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#. ``install.d``
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#. ``post-install.d``
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#. ``block-device.d``
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#. ``finalise.d``
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#. ``cleanup.d``
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``root.d``
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Create or adapt the initial root filesystem content. This is where
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alternative distribution support is added, or customisations such as
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building on an existing image.
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@ -56,60 +77,81 @@ in the phase subdirectories and store data files elsewhere in the element.
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to blindly overwrite but instead to adapt the context extracted by other
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elements.
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* runs: outside chroot
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* inputs: $ARCH=i386|amd64|armhf $TARGET\_ROOT=/path/to/target/workarea
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* runs: **outside chroot**
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* inputs:
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* extra-data.d: pull in extra data from the host environment that hooks may
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* ``$ARCH=i386|amd64|armhf``
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* ``$TARGET_ROOT=/path/to/target/workarea``
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``extra-data.d``
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Pull in extra data from the host environment that hooks may
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need during image creation. This should copy any data (such as SSH keys,
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http proxy settings and the like) somewhere under $TMP\_HOOKS\_PATH.
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http proxy settings and the like) somewhere under ``$TMP_HOOKS_PATH``.
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* runs: outside chroot
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* inputs: $TMP\_HOOKS\_PATH
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* outputs: None
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* runs: **outside chroot**
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* inputs: ``$TMP_HOOKS_PATH``
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* outputs: None
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* pre-install.d: Run code in the chroot before customisation or packages are
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installed. A good place to add apt repositories.
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``pre-install.d``
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Run code in the chroot before customisation or packages are installed. A good
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place to add apt repositories.
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* runs: in chroot
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* runs: **in chroot**
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* install.d: Runs after pre-install.d in the chroot. This is a good place to
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install packages, chain into configuration management tools or do other
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image specific operations.
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``install.d``
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Runs after ``pre-install.d`` in the chroot. This is a good place to
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install packages, chain into configuration management tools or do other image
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specific operations.
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* runs: in chroot
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* runs: **in chroot**
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* post-install.d: Run code in the chroot. This is a good place to perform
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tasks you want to handle after the OS/application install but before the
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first boot of the image. Some examples of use would be: Run chkconfig
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to disable unneeded services and clean the cache left by the package
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manager to reduce the size of the image.
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``post-install.d``
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Run code in the chroot. This is a good place to perform tasks you want to
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handle after the OS/application install but before the first boot of the
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image. Some examples of use would be:
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* runs: in chroot
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Run ``chkconfig`` to disable unneeded services
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* block-device.d: customise the block device that the image will be made on
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(e.g. to make partitions). Runs after the target tree has been fully
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populated but before the cleanup hook runs.
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Clean the cache left by the package manager to reduce the size of the image.
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* runs: outside chroot
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* inputs: $IMAGE\_BLOCK\_DEVICE={path} $TARGET\_ROOT={path}
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* outputs: $IMAGE\_BLOCK\_DEVICE={path}
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* runs: **in chroot**
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* finalise.d: Perform final tuning of the root filesystem. Runs in a chroot
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after the root filesystem content has been copied into the mounted
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filesystem: this is an appropriate place to reset SELinux metadata, install
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grub bootloaders and so on. Because this happens inside the final image, it
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is important to limit operations here to only those necessary to affect the
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filesystem metadata and image itself. For most operations, post-install.d
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is preferred.
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``block-device.d``
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Customise the block device that the image will be made on (for example to
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make partitions). Runs after the target tree has been fully populated but
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before the ``cleanup.d`` phase runs.
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* runs: in chroot
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* runs: **outside chroot**
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* inputs:
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* cleanup.d: Perform cleanup of the root filesystem content. For
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instance, temporary settings to use the image build environment HTTP proxy
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are removed here in the dpkg element.
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* ``$IMAGE_BLOCK_DEVICE={path}``
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* ``$TARGET_ROOT={path}``
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* outputs: ``$IMAGE_BLOCK_DEVICE={path}``
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``finalise.d``
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Perform final tuning of the root filesystem. Runs in a chroot after the root
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filesystem content has been copied into the mounted filesystem: this is an
|
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appropriate place to reset SELinux metadata, install grub bootloaders and so
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on.
|
||||
|
||||
Because this happens inside the final image, it is important to limit
|
||||
operations here to only those necessary to affect the filesystem metadata and
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image itself. For most operations, ``post-install.d`` is preferred.
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* runs: **in chroot**
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``cleanup.d``
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Perform cleanup of the root filesystem content. For instance, temporary
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settings to use the image build environment HTTP proxy are removed here in
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the dpkg element.
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* runs: outside chroot
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* inputs:
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* ``$ARCH=i386|amd64|armhf``
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* ``$TARGET_ROOT=/path/to/target/workarea``
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* runs: outside chroot
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* inputs: $ARCH=i386|amd64|armhf $TARGET\_ROOT=/path/to/target/workarea
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Other Subdirectories
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^^^^^^^^^^^^^^^^^^^^
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@ -117,35 +159,42 @@ Other Subdirectories
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Elements may have other subdirectories that are processed by specific elements
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rather than the diskimage-builder tools themselves.
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One example of this is the ``bin`` directory. The ``rpm-distro``, ``dpkg`` and
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``opensuse`` elements install all files found in the ``bin`` directory into
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``/usr/local/bin`` within the image as executable files.
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One example of this is the ``bin`` directory. The `rpm-distro`,
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:doc:`../elements/dpkg/README` and :doc:`../elements/opensuse/README` elements
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install all files found in the ``bin`` directory into ``/usr/local/bin`` within
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the image as executable files.
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Environment Variables
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^^^^^^^^^^^^^^^^^^^^^
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To set environment variables for other hooks, add a file to environment.d.
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To set environment variables for other hooks, add a file to your element
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``environment.d``.
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This directory contains bash script snippets that are sourced before running
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scripts in each phase.
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DIB exposes an internal IMAGE\_ELEMENT variable which provides elements access
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to the full set of elements that are included in the image build. This can
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be used to process local in-element files across all the elements
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(pkg-map for example).
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DIB exposes an internal ``$IMAGE_ELEMENT`` variable which provides elements
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access to the full set of elements that are included in the image build. This
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can be used to process local in-element files across all the elements
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(``pkg-map`` for example).
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Dependencies
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^^^^^^^^^^^^
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Each element can use the following files to define or affect dependencies:
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* element-deps: a plain text, newline separated list of elements which will
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be added to the list of elements built into the image at image creation time.
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``element-deps``
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A plain text, newline separated list of elements which will be added to the
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list of elements built into the image at image creation time.
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* element-provides: A plain text, newline separated list of elements which
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are provided by this element. These elements will be excluded from elements
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built into the image at image creation time. For example if element A depends
|
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on element B and element C includes element B in its "element-provides"
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file and A and C are included when building an image, then B is not used.
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``element-provides``
|
||||
A plain text, newline separated list of elements which are provided by this
|
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element. These elements will be excluded from elements built into the image
|
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at image creation time.
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|
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For example if element A depends on element B and element C includes element B
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in its ``element-provides`` file and A and C are included when building an
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image, then B is not used.
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Operating system elements
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^^^^^^^^^^^^^^^^^^^^^^^^^
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@ -166,18 +215,21 @@ Ramdisk Elements
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Ramdisk elements support the following files in their element directories:
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* binary-deps.d : text files listing executables required to be fed into the
|
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ramdisk. These need to be present in $PATH in the build chroot (i.e. need to
|
||||
be installed by your elements as described above).
|
||||
``binary-deps.d``
|
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Text files listing executables required to be fed into the ramdisk. These
|
||||
need to be present in ``$PATH`` in the build chroot (i.e. need to be installed
|
||||
by your elements as described above).
|
||||
|
||||
* init.d : POSIX shell script fragments that will be appended to the default
|
||||
script executed as the ramdisk is booted (/init).
|
||||
``init.d``
|
||||
POSIX shell script fragments that will be appended to the default script
|
||||
executed as the ramdisk is booted (``/init``).
|
||||
|
||||
* ramdisk-install.d : called to copy files into the ramdisk. The variable
|
||||
TMP\_MOUNT\_PATH points to the root of the tree that will be packed into
|
||||
the ramdisk.
|
||||
``ramdisk-install.d``
|
||||
Called to copy files into the ramdisk. The variable ``$TMP_MOUNT_PATH`` points
|
||||
to the root of the tree that will be packed into the ramdisk.
|
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|
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* udev.d : udev rules files that will be copied into the ramdisk.
|
||||
``udev.d``
|
||||
``udev`` rules files that will be copied into the ramdisk.
|
||||
|
||||
Element coding standard
|
||||
^^^^^^^^^^^^^^^^^^^^^^^
|
||||
@ -189,20 +241,24 @@ Element coding standard
|
||||
- `do` and `then` keywords should be on the same line as the if, while or
|
||||
for conditions.
|
||||
|
||||
.. _dev-global-image-build-variables:
|
||||
|
||||
Global image-build variables
|
||||
----------------------------
|
||||
|
||||
* DIB\_OFFLINE : this is always set. When not empty, any operations that
|
||||
perform remote data access should avoid it if possible. If not possible
|
||||
the operation should still be attempted as the user may have an external
|
||||
cache able to keep the operation functional.
|
||||
``DIB_OFFLINE``
|
||||
This is always set. When not empty, any operations that perform remote data
|
||||
access should avoid it if possible. If not possible the operation should still
|
||||
be attempted as the user may have an external cache able to keep the operation
|
||||
functional.
|
||||
|
||||
* DIB\_IMAGE\_ROOT\_FS\_UUID : this contains the UUID of the root fs, when
|
||||
diskimage-builder is building a disk image. This works only for ext
|
||||
filesystems.
|
||||
``DIB_IMAGE_ROOT_FS_UUID``
|
||||
This contains the UUID of the root filesystem, when diskimage-builder is
|
||||
building a disk image. This works only for ext filesystems.
|
||||
|
||||
* DIB\_IMAGE\_CACHE : path to where cached inputs to the build process
|
||||
are stored. Defaults to ~/.cache/image_create.
|
||||
``DIB_IMAGE_CACHE``
|
||||
Path to where cached inputs to the build process are stored. Defaults to
|
||||
``~/.cache/image_create``.
|
||||
|
||||
Structure of an element
|
||||
-----------------------
|
||||
@ -256,26 +312,26 @@ place it into a directory on the target image during the extra-data phase. The
|
||||
default location/branch can then be overridden by the process running
|
||||
diskimage-builder, making it possible to use the same element to track more
|
||||
then one branch of a git repository or to get source for a local cache. See
|
||||
elements/source-repositories/README.md for more information.
|
||||
:doc:`../elements/source-repositories/README` for more information.
|
||||
|
||||
Debugging elements
|
||||
------------------
|
||||
|
||||
The build-time environment and command line arguments are captured by the
|
||||
'base' element and written to /etc/dib\_environment and /etc/dib\_arguments
|
||||
inside the image.
|
||||
:doc:`../elements/base/README` element and written to ``/etc/dib_environment``
|
||||
and ``/etc/dib_arguments`` inside the image.
|
||||
|
||||
Export 'break' to drop to a shell during the image build. Break points can be
|
||||
Export ``break`` to drop to a shell during the image build. Break points can be
|
||||
set either before or after any of the hook points by exporting
|
||||
"break=[before|after]-hook-name". Multiple break points can be specified as a
|
||||
comma-delimited string. Some examples:
|
||||
|
||||
* break=before-block-device-size will break before the block device size hooks
|
||||
are called.
|
||||
* ``break=before-block-device-size`` will break before the block device size
|
||||
hooks are called.
|
||||
|
||||
* break=before-pre-install will break before the pre-install hooks.
|
||||
* ``break=before-pre-install`` will break before the pre-install hooks.
|
||||
|
||||
* break=after-error will break after an error during a in target hookpoint.
|
||||
* ``break=after-error`` will break after an error during an in target hookpoint.
|
||||
|
||||
Images are built such that the Linux kernel is instructed not to switch into
|
||||
graphical consoles (i.e. it will not activate KMS). This maximises
|
||||
@ -286,7 +342,7 @@ console so nova's console-log command can function. There is an element in the
|
||||
tripleo-image-elements repository called "remove-serial-console" which will
|
||||
force all boot messages to appear on the main console.
|
||||
|
||||
Ramdisk images can be debugged at run-time by passing "troubleshoot" as a
|
||||
Ramdisk images can be debugged at run-time by passing ``troubleshoot`` as a
|
||||
kernel command line argument, or by pressing "t" when an error is reached. This
|
||||
will spawn a shell on the console (this can be extremely useful when network
|
||||
interfaces or disks are not detected correctly).
|
||||
@ -294,42 +350,53 @@ interfaces or disks are not detected correctly).
|
||||
Testing Elements
|
||||
----------------
|
||||
|
||||
An element can have functional tests encapsulated inside the element itself. In
|
||||
order to create a test case, follow these steps:
|
||||
An element can have functional tests encapsulated inside the element itself. The
|
||||
tests can be written either as shell or python unit tests.
|
||||
|
||||
* Create a directory called 'test-elements' inside your element.
|
||||
shell
|
||||
"""""
|
||||
|
||||
In order to create a test case, follow these steps:
|
||||
|
||||
* Create a directory called ``test-elements`` inside your element.
|
||||
|
||||
* Inside the test-elements directory, create a directory with the name of your
|
||||
test case. The test case directory should have the same structure as an
|
||||
element.
|
||||
i.e. elements/apt-sources/test-elements/test-case-1
|
||||
element. For example::
|
||||
|
||||
elements/apt-sources/test-elements/test-case-1
|
||||
|
||||
* Assert state during each of the element build phases you would like to test.
|
||||
You can exit 1 to indicate a failure.
|
||||
|
||||
* To exit early and indicate a success, touch a file /tmp/dib-test-should-fail
|
||||
in the image chroot, then exit 1.
|
||||
* To exit early and indicate a success, touch a file
|
||||
``/tmp/dib-test-should-fail`` in the image chroot, then exit 1.
|
||||
|
||||
python
|
||||
""""""
|
||||
|
||||
Additionally, elements can be tested using python unittests. To create a
|
||||
a python test:
|
||||
|
||||
* Create a directory called 'tests' in the element directory.
|
||||
* Create a directory called ``tests`` in the element directory.
|
||||
|
||||
* Create an empty file called '\_\_init\_\_.py' to make it into a python
|
||||
* Create an empty file called ``__init__.py`` to make it into a python
|
||||
package.
|
||||
|
||||
* Create your test files as 'test\_whatever.py', using regular python test
|
||||
* Create your test files as ``test\whatever.py``, using regular python test
|
||||
code.
|
||||
|
||||
To run all the tests use testr - `testr run`. To run just some tests provide
|
||||
To run all the tests use testr - ``testr run``. To run just some tests provide
|
||||
one or more regex filters - tests matching any of them are run -
|
||||
`testr run apt-proxy`.
|
||||
``testr run apt-proxy``.
|
||||
|
||||
Third party elements
|
||||
--------------------
|
||||
|
||||
Additional elements can be incorporated by setting ELEMENTS_PATH, for example
|
||||
if one were building tripleo-images, the variable would be set like::
|
||||
Additional elements can be incorporated by setting ``ELEMENTS_PATH``, for
|
||||
example if one were building tripleo-images, the variable would be set like:
|
||||
|
||||
export ELEMENTS_PATH=tripleo-image-elements/elements
|
||||
disk-image-create rhel7 cinder-api
|
||||
.. sourcecode:: sh
|
||||
|
||||
export ELEMENTS_PATH=tripleo-image-elements/elements
|
||||
disk-image-create rhel7 cinder-api
|
||||
|
||||
Loading…
Reference in New Issue
Block a user