If a configuration requires creating a set of colocated resources that start in order, such as resource A before B, and B before C, configure a resource group containing those resources.

There are some situations, however, where configuring the resources that need to start in a specified order as a resource group is not appropriate:

• You may need to configure resources to start in order and the resources are not necessarily colocated.
• You may have a resource C that must start after either resource A or B has started but there is no relationship between A and B.
• You may have resources C and D that must start after both resources A and B have started, but there is no relationship between A and B or between C and D.

In these situations, you can create an ordering constraint on a set or sets of resources with the pcs constraint order set command.

You can set the following options for a set of resources with the pcs constraint order set command.

• sequential, which can be set to true or false to indicate whether the set of resources must be ordered relative to each other. The default value is true.

  Setting sequential to false allows a set to be ordered relative to other sets in the ordering constraint, without its members being ordered relative to each other. Therefore, this option makes sense only if multiple sets are listed in the constraint; otherwise, the constraint has no effect.

• require-all, which can be set to true or false to indicate whether all of the resources in the set must be active before continuing. Setting require-all to false means that only one resource in the set needs to be started before continuing on to the next set. Setting require-all to false has no effect unless used in conjunction with unordered sets, which are sets for which sequential is set to false. The default value is true.
• action, which can be set to start, promote, demote or stop.
• role, which can be set to Stopped, Started, Promoted, or Unpromoted.

You can set the following constraint options for a set of resources following the setoptions parameter of the pcs constraint order set command.

• id, to provide a name for the constraint you are defining.
• kind, which indicates how to enforce the constraint.
• symmetrical, to set whether the reverse of the constraint applies for the opposite action.

# pcs constraint order set resource1resource2 [resourceN]... [options] [set resourceXresourceY ... [options]] [setoptions [constraint_options]]

If you have three resources named D1, D2, and D3, the following command configures them as an ordered resource set.

# pcs constraint order set D1 D2 D3

If you have six resources named A, B, C, D, E, and F, this example configures an ordering constraint for the set of resources that will start as follows:

• A and B start independently of each other
• C starts once either A or B has started
• D starts once C has started
• E and F start independently of each other once D has started

Stopping the resources is not influenced by this constraint since symmetrical=false is set.

# pcs constraint order set A B sequential=false require-all=false set C D set E F sequential=false setoptions symmetrical=false