6.2.3. Ordered Resource Sets

A common situation is for an administrator to create a chain of ordered resources, where, for example, resource A starts before resource B which starts before resource C. If your configuration requires that you create a set of resources that is colocated and started in order, you can configure a resource group that contains those resources, as described in Section 5.5, “Resource Groups”. If, however, you need to configure resources to start in order and the resources are not necessarily colocated, you can create an order 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.
    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.
  • action, which can be set to start, promote, demote or stop, as described in Table 6.2, “Properties of an Order Constraint”.
You can set the following constraint options for a set of resources following the setoptions parameter of the pcs constraint order set command.
pcs constraint order set resource1 resource2 [resourceN]... [options] [set resourceX resourceY ... [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