A data security manager in a multi-nodal environment enforces processing constraints stored as security relationships that control how different pieces of a multi-nodal application (called execution units) are allowed to execute to insure data security. The security manager preferably checks the security relationships for security violations when new execution units start execution, when data moves to or from an execution unit, and when an execution unit requests external services. Where the security manager determines there is a security violation based on the security relationships, the security manager may move, delay or kill an execution unit to maintain data security.