Google has added a new firewall feature to their cloud offering. Currently in beta, the App Engine firewall, which is in beta, lets developers specify a set of rules, order them by priority and specify an IP address or a set of IP addresses. These are used to block or allow access to an application.
The new Firewall rules options are available through the App Engine settings page. Google has provided instructions on how it works and some set up instructions on their Cloud Platform Blog.
While firewalls aren't the most powerful security measure we have at out disposal, they remain part of a layered approach to security. Being able to manage traffic in and out of an application or network remains a valid part of any security strategy. This step, by Google, is a good move. Aside from offering another layer of protection, it does so in a way that won't make life hard for developers.
Amazon and Azure offer their own application firewall features as well.