Dependencies in PSDeploy are simply an option to help you determine the order of deployments. Perhaps you want to deploy infrastructure before deploying the services running over them, or deploy a node before deploying a file to it.

First, let's look at the typical order of operations:

Deploy A {
    By FileSystem Two {
        FromSource MyModule
        To C:\PSDeployTo
    }

    By FileSystem Three {
        FromSource MyModule
        To C:\PSDeployTo
    }
}

Deploy B {
    By FileSystem One {
        FromSource MyModule
        To C:\PSDeployTo
    }
}

PSDeploy processes items in the order that it reads them. But, you might have a reason to alter this behavior. We can use the DependingOn function for this. It takes one or more DeploymentNames to depend on.

Keep in mind that a DeploymentName will be in the format DeploymentName-ByName if you name a By block

Deploy A {
    By FileSystem Two {
        FromSource MyModule
        To C:\PSDeployTo
        DependingOn One
    }

    By FileSystem Three {
        FromSource MyModule
        To C:\PSDeployTo
        DependingOn Two
    }
}

Deploy B {
    By FileSystem One {
        FromSource MyModule
        To C:\PSDeployTo
    }
}

Invoke-PSDeploy will respect these dependencies.

Note: Developers out there... I borrowed a topological sort from stackoverflow. It seemed to work with everything I threw at it, but if you spot any issues, pull requests would be welcome!