1. A method for selecting a network implementation using network policies within a virtualization environment, the method comprising: receiving, by a control program executing within a virtualization environment on a computing device, an event notification generated by a virtual machine responsive to a lifecycle event; invoking, by the control program responsive to receiving the event notification, a policy engine; applying, by the policy engine, a network policy to existing network configurations of the virtualization environment, the network policy corresponding to the virtual machine; identifying, by the policy engine, an existing network configuration having attributes that satisfy the network policy; and selecting, by the policy engine, a network implementation that satisfies the network policy and the network configuration.