BOS supports an optional limit parameter when creating a session.
This parameter can be used to further limit the nodes that BOS runs against, and is applied to all
boot sets.
The limit parameter takes a comma-separated list of nodes, groups, or roles in any combination.
The BOS session will be limited to run against components that match both the boot set information
and one or more of the nodes, groups, or roles listed in the limit.
For more details on creating a session, see Create a session.
When specifying nodes, component names (xnames) must be used. The use of
NIDs is not supported.
In order to prevent the accidental creation of sessions attempting to use NIDs, the
reject_nids option may be enabled.
If the session_limit_required option is enabled,
then the limit parameter is not optional when creating a session.
However, even if this option is enabled, it is still possible to use
Advanced session limit syntax to effectively create a
session with no limit; a session can be limited to all nodes on the system by specifying
* as the limit parameter (if this is done on the command line, it must be quoted in
order to prevent it from being interpreted by the shell).
The use of a session limit will not allow a tenant-owned
session template to include
components it does not own in the
nodes_list
field of a boot set. For more information, see
Tenant-owned session templates.
The table below describes the operations that can be used to further limit the scope of a BOS session. Components are treated as OR operations unless preceded by one of the operations listed in the following table.
| Operation | Description |
|---|---|
& |
Added to the beginning of a group or role to specify an intersection of groups. |
! |
Added to the beginning of a node, group, or role to exclude it. |
all |
When only trying to exclude a node or group, the limit must start with all. |
* |
Same as all |
The table below helps demonstrate the logic used with the limit parameter and includes examples
of how to limit against different nodes, groups, and roles.
| Description | Pattern | Targets |
|---|---|---|
| All nodes | all or * (or leave empty) |
All nodes |
| One node | node1 |
node1 |
| Multiple nodes | node1,node2 |
node1 and node2 |
| Excluding a node | all,!node1 |
All nodes except node1 |
| One group | group1 |
Nodes in group1 |
| Multiple groups | group1,group2 |
Nodes in group1 or group2 |
| Excluding groups | group1,!group2 |
Nodes in group1 but not in group2 |
| Intersection of groups | group1,&group2 |
Nodes in both group1 and group2 |
The limit parameter for BOS works similarly to the --ansible-limit parameter for
the Configuration Framework Service (CFS),
as well as the limit parameter for Ansible. Some limitations do apply for those familiar with the Ansible syntax.
BOS accepts only a comma-separated list, not colons, and does not support regular expressions in the patterns.
For more information on what it means to provide a limit in CFS/Ansible, see
Specifying Hosts and Groups.