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Chapter 15. Displaying resource constraints and resource dependencies

There are a several commands you can use to display constraints that have been configured. You can display all configured resource constraints, or you can limit the display of esource constraints to specific types of resource constraints. Additionally, you can display configured resource dependencies.

Displaying all configured constraints

The following command lists all current location, order, and colocation constraints. If the --full option is specified, show the internal constraint IDs. 

pcs constraint [list|show] [--full]

As of RHEL 8.2, listing resource constraints no longer by default displays expired constraints. To include expired constaints in the listing, use the --all option of the pcs constraint command. This will list expired constraints, noting the constraints and their associated rules as (expired) in the display.

Displaying location constraints

The following command lists all current location constraints.

  • If resources is specified, location constraints are displayed per resource. This is the default behavior.
  • If nodes is specified, location constraints are displayed per node.
  • If specific resources or nodes are specified, then only information about those resources or nodes is displayed. 
pcs constraint location [show [resources [resource...]] | [nodes [node...]]] [--full]

Displaying ordering constraints

The following command lists all current ordering constraints. 

pcs constraint order [show]

Displaying colocation constraints

The following command lists all current colocation constraints. 

pcs constraint colocation [show]

Displaying resource-specific constraints

The following command lists the constraints that reference specific resources. 

pcs constraint ref resource ...

Displaying resource dependencies (Red Hat Enterprise Linux 8.2 and later)

The following command displays the relations between cluster resources in a tree structure. 

pcs resource relations resource [--full]

If the --full option is used, the command displays additional information, including the constraint IDs and the resource types.

In the following example, there are 3 configured resources: C, D, and E. 

# pcs constraint order start C then start D
Adding C D (kind: Mandatory) (Options: first-action=start then-action=start)
# pcs constraint order start D then start E
Adding D E (kind: Mandatory) (Options: first-action=start then-action=start)

# pcs resource relations C
C
`- order
   |  start C then start D
   `- D
      `- order
         |  start D then start E
         `- E
# pcs resource relations D
D
|- order
|  |  start C then start D
|  `- C
`- order
   |  start D then start E
   `- E
# pcs resource relations E
E
`- order
   |  start D then start E
   `- D
      `- order
         |  start C then start D
         `- C

In the following example, there are 2 configured resources: A and B. Resources A and B are part of resource group G. 

# pcs resource relations A
A
`- outer resource
   `- G
      `- inner resource(s)
         |  members: A B
         `- B
# pcs resource relations B
B
`- outer resource
   `- G
      `- inner resource(s)
         |  members: A B
         `- A
# pcs resource relations G
G
`- inner resource(s)
   |  members: A B
   |- A
   `- B