Add info on tinyipa to docs

Mention tinyipa in Image Builders section and in troubleshooting.

Change-Id: Ic6cfe64255aba0460cc960a98b18580b7798b204

doc/source/index.rst

@@ -177,6 +177,26 @@ Another way to build a ramdisk image for IPA is by using diskimage-builder
 [3]_. The ironic-agent diskimage-builder element builds the IPA ramdisk, which
 installs all the required packages and configures services as needed.
 
+tinyipa
+~~~~~~~
+
+Ironic Python Agent repo also provides a set of scripts to build a
+Tiny Core Linux-based deployment kernel and ramdisk (code name ``tinyipa``)
+under ``imagebuild/tinyipa`` folder.
+
+`Tiny Core Linux <http://tinycorelinux.net/>`_
+is a very minimalistic Linux distribution.
+Due to its small size and decreased RAM requirements
+it is mostly suitable for usage in CI with virtualized hardware,
+and is already used on a number of gate jobs in projects under
+OpenStack Baremetal program.
+On the other hand, due to its generally newer Linux kernel it also known to
+work on real hardware if the kernel supports all necessary components
+installed.
+
+Please refer to ``imagebuild/tinyipa/README.rst`` for more information and
+build instructions.
+
 ISO Images
 ~~~~~~~~~~
 Additionally, the IPA ramdisk can be packaged inside of an ISO for use with

doc/source/troubleshooting.rst

@@ -46,6 +46,27 @@ devuser element example::
   export DIB_DEV_USER_AUTHORIZED_KEYS=$HOME/.ssh/id_rsa.pub
   disk-image-create -o /path/to/custom-ipa debian ironic-agent devuser
 
+tinyipa
+~~~~~~~
+
+If you want to enable SSH access to the image,
+set ``ENABLE_SSH`` variable in your shell to ``true`` before building
+the tinyipa image::
+
+  export ENABLE_SSH=true
+
+By default it will use default public RSA (or, if not available, DSA)
+key of the user running the build (``~/.ssh/id_{rsa,dsa}.pub``).
+
+To provide other public SSH key, export full path to it in your shell
+before building tinyipa as follows::
+
+  export SSH_PUBLIC_KEY=/path/to/other/ssh/public/key
+
+The user to use for access is default Tiny Core Linux user ``tc``.
+This user has no password and has password-less ``sudo`` permissions.
+Installed SSH server is configured to disable Password authentication.
+
 Access via console
 ------------------
 If you need to use console access, passwords must be enabled there are a
@@ -112,6 +133,13 @@ Example::
   export DIB_DEV_USER_PASSWORD=PASSWORD
   disk-image-create -o /path/to/custom-ipa debian ironic-agent devuser
 
+tinyipa
+~~~~~~~
+
+The image built with scripts provided in ``imagebuild/tinyipa`` folder
+of Ironic Python Agent repository by default auto-logins the default
+Tiny Core Linux user ``tc`` to the console.
+This user has no password and has password-less ``sudo`` permissions.
 
 Set IPA to debug logging
 ========================