Prettify 'Developing Elements' documentation
Augment the developing_elements.rst by taking advantage of Sphinx markup. Most of the doc used to be in /README.md and thus did not leverage on Sphinx. Use inline codeblock to denote variables, files, command: ``foo`` Phase Subdirectories: List phase names in the preliminary introduction Get rid of lists in favor of definitions Highlight whether the phase runs in or outside the chroot Input parameters are now lists Use definition lists in Dependencies and Ramdisk sections. Link to elements README when they exist. Testing Element: split into two subsections: 'shell' and 'python'. Use "sourcecode:: sh" for the couple examples at the very top and very bottom of the document. Change-Id: I2421f76ec452cac243ccb2208f88c7d320ffedd3
This commit is contained in:
Antoine Musso
parent
6afe6577ac
commit
e8cecab45c
@ -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.
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Because this happens inside the final image, it is important to limit
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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``
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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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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 $PATH in the build chroot (i.e. need to
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be installed by your elements as described above).
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``binary-deps.d``
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Text files listing executables required to be fed into the ramdisk. These
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need to be present in ``$PATH`` in the build chroot (i.e. need to be installed
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by your elements as described above).
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* init.d : POSIX shell script fragments that will be appended to the default
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script executed as the ramdisk is booted (/init).
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``init.d``
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POSIX shell script fragments that will be appended to the default script
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executed as the ramdisk is booted (``/init``).
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* ramdisk-install.d : called to copy files into the ramdisk. The variable
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TMP\_MOUNT\_PATH points to the root of the tree that will be packed into
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the ramdisk.
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``ramdisk-install.d``
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Called to copy files into the ramdisk. The variable ``$TMP_MOUNT_PATH`` points
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to the root of the tree that will be packed into the ramdisk.
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* udev.d : udev rules files that will be copied into the ramdisk.
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``udev.d``
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``udev`` rules files that will be copied into the ramdisk.
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Element coding standard
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^^^^^^^^^^^^^^^^^^^^^^^
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@ -189,20 +241,24 @@ Element coding standard
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- `do` and `then` keywords should be on the same line as the if, while or
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for conditions.
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.. _dev-global-image-build-variables:
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Global image-build variables
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----------------------------
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* DIB\_OFFLINE : this is always set. When not empty, any operations that
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perform remote data access should avoid it if possible. If not possible
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the operation should still be attempted as the user may have an external
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cache able to keep the operation functional.
|
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``DIB_OFFLINE``
|
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This is always set. When not empty, any operations that perform remote data
|
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access should avoid it if possible. If not possible the operation should still
|
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be attempted as the user may have an external cache able to keep the operation
|
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functional.
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* DIB\_IMAGE\_ROOT\_FS\_UUID : this contains the UUID of the root fs, when
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diskimage-builder is building a disk image. This works only for ext
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filesystems.
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``DIB_IMAGE_ROOT_FS_UUID``
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This contains the UUID of the root filesystem, when diskimage-builder is
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building a disk image. This works only for ext filesystems.
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* DIB\_IMAGE\_CACHE : path to where cached inputs to the build process
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are stored. Defaults to ~/.cache/image_create.
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``DIB_IMAGE_CACHE``
|
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Path to where cached inputs to the build process are stored. Defaults to
|
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``~/.cache/image_create``.
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Structure of an element
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-----------------------
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@ -256,26 +312,26 @@ place it into a directory on the target image during the extra-data phase. The
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default location/branch can then be overridden by the process running
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diskimage-builder, making it possible to use the same element to track more
|
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then one branch of a git repository or to get source for a local cache. See
|
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elements/source-repositories/README.md for more information.
|
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:doc:`../elements/source-repositories/README` for more information.
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Debugging elements
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------------------
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The build-time environment and command line arguments are captured by the
|
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'base' element and written to /etc/dib\_environment and /etc/dib\_arguments
|
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inside the image.
|
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:doc:`../elements/base/README` element and written to ``/etc/dib_environment``
|
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and ``/etc/dib_arguments`` inside the image.
|
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|
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Export 'break' to drop to a shell during the image build. Break points can be
|
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Export ``break`` to drop to a shell during the image build. Break points can be
|
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set either before or after any of the hook points by exporting
|
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"break=[before|after]-hook-name". Multiple break points can be specified as a
|
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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.
|
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* ``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…
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Reference in New Issue
Block a user