Mario Villaplana 689dbf6b5c Add documentation for rescue mode

This adds documentation for rescue mode, including the finalize_rescue
command as well as upstream support in agent images.

Change-Id: Id0834941ee4dacf2e7c0feaa65126d63e8a97c39
Partial-Bug: 1526449

2018-02-07 11:08:15 -05:00

2.0 KiB

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Rescue mode

Overview

Rescue mode is a feature that can be used to boot a ramdisk for a tenant in case the machine is otherwise inaccessible. For example, if there's a disk failure that prevents access to another operating system, rescue mode can be used to diagnose and fix the problem.

Support in ironic-python-agent images

Rescue is initiated when ironic-conductor sends the finalize_rescue command to ironic-python-agent. A user rescue is created with a password provided as an argument to this command. DHCP is then configured to facilitate network connectivity, thus enabling a user to login to the machine in rescue mode.

Warning

Rescue mode exposes the contents of the ramdisk to the tenant. Ensure that any rescue image you build does not contain secrets (e.g. sensitive clean steps, proprietary firmware blobs).

The below has information about supported images that may be built to use rescue mode.

CoreOS

The CoreOS image supports rescue mode when used with DHCP tenant networks. You may follow the normal process for building a CoreOS ironic-python-agent image to create an image that supports rescue mode.

After the finalize_rescue command completes, DHCP will be configured on all network interfaces, and a rescue user will be created with the specified rescue_password.

TinyIPA

The TinyIPA image supports rescue mode when used with DHCP tenant networks. No special action is required to build a TinyIPA image with this support.