Control device, control system, control method, and control program

In the present invention, when a cloud controller (50) detects an attack on any of the virtual machines (VMs) in a data center in a system, a network address translation (NAT) setting is performed for the private IP address of the VM(A) in the boundary router (30) of each data center (2, 3) other than the data center (1) to which the VM(A) subject to the attack belongs. Next, the cloud controller (50) makes a setting with respect to a redirect device (70) in the same data center (1) as the VM(A) so as to redirect access from a user terminal (10) to a host under the control of one of the boundary routers (30B, 30C) of the data centers (2, 3) other than the data center (1). Next, the cloud controller (50) changes the private IP address of the VM(A) in the NAT setting of the boundary router (30A) in the data center (1) to the private IP address of the redirect device (70).