Document installing from ISOs in OpenStack (#708)

Add user guide for crearting and installing instances from ISOs in
OpenStack using the rescue mode.

Signed-off-by: Jan Horstmann <[email protected]>

docs/guides/user-guide/openstack/install-instance-from-iso.md

@@ -0,0 +1,118 @@
+---
+sidebar_label: Install instance from ISO image
+---
+
+# Install instance from ISO image
+
+While in general it is considered best practice to create instances from existing or specially crafted images, sometimes it is necessary to install an instance using a traditional installer packaged in an ISO image.
+One way to do this in OpenStack is to leverage the [instance rescue mechanism](https://docs.openstack.org/nova/latest/user/rescue.html), which allows to boot an instance from another imagewhile providing access to the instances storage.
+
+## Upload the ISO image
+
+If the required ISO image is not available in the image store yet upload it first:
+
+```
+PATH_TO_ISO_IMAGE=""
+IMAGE_NAME=""
+openstack image create \
+  --disk-format iso \
+  --file $PATH_TO_ISO_IMAGE \
+  --property hw_rescue_device=disk \
+  --property hw_rescue_bus=virtio \
+  $IMAGE_NAME
+```
+
+The `hw_rescue_device` and `hw_rescue_bus` properties may be omitted if you do not intent to create an instance from a boot volume.
+
+## Creating the instance
+
+### Using nova local storage
+
+Create an instance with a blank local boot device, e.g.:
+
+Until [this bug](https://bugs.launchpad.net/nova/+bug/2090926) is fixed, one cannot create an instance with a blank local boot device. As a workaround create an unbootable dummy image first, e.g.:
+
+```
+DUMMY_IMAGE_NAME="dummy"
+dd if=/dev/zero of="$DUMMY_IMAGE_NAME" bs=1k count=1
+openstack image create \
+  --file "$DUMMY_IMAGE_NAME" \
+  "$DUMMY_IMAGE_NAME"
+rm  "$DUMMY_IMAGE_NAME"
+```
+
+Create the instance:
+
+```
+INSTANCE_NAME=""
+FLAVOR=""
+openstack server create \
+  --flavor "$FLAVOR" \
+  --image "$DUMMY_IMAGE_NAME" \
+  --no-network \
+  "$INSTANCE_NAME"
+```
+
+Once the bug is fixed the instance may be created directly:
+
+```
+INSTANCE_NAME=""
+FLAVOR=""
+openstack server create \
+  --flavor "$FLAVOR" \
+  --block-device "source_type=blank,destination_type=local,guest_format=raw,boot_index=0" \
+  --no-network \
+  "$INSTANCE_NAME"
+```
+
+### Using boot from volume
+
+Create an instance with a blank boot volume
+
+```
+INSTANCE_NAME=""
+FLAVOR=""
+BOOT_VOLUME_SIZE=""
+openstack server create \
+  --flavor "$FLAVOR" \
+  --block-device "source_type=blank,destination_type=volume,volume_size=$BOOT_VOLUME_SIZE,boot_index=0" \
+  --no-network \
+  "$INSTANCE_NAME"
+```
+
+Set the created volume to bootable
+
+```
+openstack volume set --bootable $(openstack server show $INSTANCE_NAME -f json -c attached_volumes | jq -r '.attached_volumes | first | .id')
+```
+
+## Install the created instance from the uploaded ISO 
+
+Use the rescue mechanism to boot the ISO, e.g.:
+
+```
+openstack server rescue \
+  --image $IMAGE_NAME \
+  $INSTANCE_NAME
+```
+
+Wait for the instance to be rescued. This will take a moment, as a soft reboot is tried before issueing a hard reboot.
+Watch the instance `task_state` and `status` to see the latter change from `ACTIVE` to `RESCUE`.
+
+```
+watch openstack server show $INSTANCE_NAME -f value -c status -c task_state
+```
+
+Start the installation procedure, e.g. by opening the instance's console
+
+```
+openstack console url show $INSTANCE_NAME
+```
+
+The instances storage device should be available as a destination for the installation.
+Rebooting the instance in this state will lead to the rescue image being booted again.
+To boot the instance from its freshly provisioned boot device unrescue the instance:
+
+```
+openstack server unrescue $INSTANCE_NAME
+```