Cloud is becoming a dominant computing platform.
However, we see few work on how to protect cloud data centers.
As a cloud usually hosts many different type of applications, the
traditional packet level firewall mechanism is not suitable for
cloud platforms in case of complex attacks. It is necessary to perform
anomaly detection at the event level. Moreover, protection
objects are more diverse than the traditional firewall. Motivated
by this, we propose a general framework of cloud firewall, which
features event level detection chain with dynamical resource
allocation. We establish a mathematical model for the proposed
framework. Moreover, a linear resource investment function is
proposed for economical dynamical resource allocation for cloud
firewalls. A few conclusions have been extracted for the reference
of cloud providers and designers