Support for node retirement

https://storyboard.openstack.org/#!/story/2005425

This spec proposes to add initial support for retiring nodes from ironic.

Retiring nodes is a natural part of a server’s life cycle, for instance when the end of the warranty is reached and the physical space is needed for new deliveries to install replacement capacity.

However, depending on the type of the deployment, removing nodes from service can be a full workflow by itself as it may include steps like moving applications to other hosts, cleaning sensitive data from disks or the BMC, or tracking the dismantling of servers from their racks.

In order to help Deployers with these tasks, ironic should provide basic means to mark nodes as being retired, i.e. mark them as not eligible for scheduling any longer (while still allowing other operations such as cleaning), or support a convenient search for and list such nodes.

Extensions of this initial support, such as extending the state machine by an explicit ‘retired’ state (which could be used as a starting point for a dedicated retirement workflow with end-of-life cleaning or other more elaborate actions, such as ‘prepare for donation’) are beyond the scope of this spec.

Problem description

There is currently no explicit support in ironic for node retirement: when a node needs to be taken out of service, the instance is deleted (which triggers cleaning) and the node is deleted, either directly from state ‘available’ or after being moved to ‘manageable’ (and potential additional cleaning).

There are at least two issues that this spec tries to fix:

  • between the deletion of the instance and the deletion of the node, there is a time window in which a new instance could be scheduled to a node on its way into retirement (setting maintenance to ‘True’ does only partially help with this scheduling race as – apart from not being meant to be used in this situation – this will prevent cleaning);

  • there is no easy way to mark nodes as ‘retired’; this makes identifying and listing such nodes (as required by third party tools or the remaining retirement workflow) cumbersome.

The retirement use case is different from other use cases, like a non-functional node which needs to be taken out of service for some time, in that nodes may be marked for retirement a long time before anything actually happens on the node. Also, retired nodes are not supposed to enter service again.

Proposed change

The proposal is to extend the list of node properties by two new fields:

  • ‘retired’ (True/False)

  • ‘retired_reason’ (text)

in analogy to the existing ‘protected’ and ‘protected_reason’.

The ‘retired’ field shall signal that a node is meant to be retired and that the node should not be considered for scheduling any longer. The ‘retired’ field can be set irrespective of the node’s state, in particular when the node is ‘active’.

Active nodes which are cleaned while ‘retired’ is True, e.g. upon instance deletion, go to ‘manageable’ (rather than ‘available’). This leaves no window where a retired node would receive another instance. Otherwise, ‘retired’ set to True shall not interfere with cleaning or rebuilding.

Nodes with ‘retired’ set to True cannot move from manageable to available (to prevent accidental re-use): the “provide” verb is blocked. In order to move these nodes to available, the ‘retired’ field needs to be set to False first.

The new field shall also be used to get these nodes quickly via a ‘list’ command, e.g. by an additional flag ‘–retired’ (in analogy to ‘–maintenance’).

Alternatives

An alternative to address the lack of support for node retirement would be to introduce a new state ‘retired’ in the ironic state diagram. While this would require additional efforts to implement, there are no obvious benefits compared to the proposal of this specification.

Using the currently available means in ironic, such as the ‘maintenance’ state and ‘maintenance_reason’, is certainly possible but will cause inconveniences during node cleaning and when trying to extract the list of nodes to be removed.

Data model impact

The ‘nodes’ table will get two additional fields:

  • ‘retired’ (tinyint)

  • ‘retired_reason’ (text)

For existing instances, i.e. for data migration, ‘retired’ will be set to False and ‘retired_reason’ will be left empty.

State Machine Impact

The ‘retired’ field can be set on nodes in any state except ‘available’. Nodes in ‘available’ should be moved to manageable first to ensure backwards compatibility with tools like metalsmith. This also eliminates the need for changes in the nova driver.

The ‘retired’ field can also be set for nodes in transient states, as long as the node is not locked.

When ‘retired’ is set to True, a node will not move to ‘available’ after cleaning, but to ‘manageable’.

When ‘retired’ is set to True, a node cannot move from ‘manageable’ to ‘available’, the corresponding ‘provide’ verb will return an HTTP 409.

REST API impact

The REST API will need to be extended with a new version to include the new ‘retired’ field, in a similar way as the protected field was introduced [0][1].

In addition, there should be a filter /v1/nodes?retired=True/False to easily identify retired nodes.

Client (CLI) impact

“ironic” CLI

None.

“openstack baremetal” CLI

The ‘–retired’ and ‘–retired-reason’ options will be added to the ‘set’ and ‘unset’ subcommands:

  • openstack baremetal node set –retired –retired-reason <reason> <node>

  • openstack baremetal node unset –retired <node>

shall be added to set and unset a node’s ‘retired’ field (and provide a reason in the case of ‘set’).

An additional flag ‘–retired’ shall be added to the ‘openstack baremetal node list’ command to restrict the returned result to the nodes which have the retired flag set.

RPC API impact

Driver API impact

None.

Nova driver impact

None.

Ramdisk impact

None.

Security impact

None.

Other end user impact

None.

Scalability impact

None.

Performance Impact

None.

Other deployer impact

None.

Developer impact

None.

Implementation

Assignee(s)

Primary assignees:

Arne Wiebalck (arne_wiebalck) Riccardo Pittau (rpittau)

Other contributors: None

Work Items

  • Add new database fields

  • Adapt state machine if ‘retired’ is set to True
    • change cleaning –> manageable

    • move available –> manageable

    • block manageable –> available

  • Exclude retired nodes from periodic tasks

  • Extend API

  • Extend cli

  • Add new API to openstacksdk

  • Add documentation

Dependencies

None.

Testing

Needs testing similar to ‘maintenance’.

Upgrades and Backwards Compatibility

Upon upgrades the new fields need to be set as specified in the ‘Data model impact’ section.

Documentation Impact

The additional ‘retired’ field and its intended use need to be documented.