Machine images have become a staple of modern deployment pipelines, and there are a number of tools and techniques to create the images. Because of its comprehensive feature set and the positive experiences we've had with it, we recommend Packer over the alternatives. We also recommend against trying to write custom scripts to do what Packer does out of the box.
We featured 'Machine image as a build artifact' in the last Radar, as an excellent way to implement fast spin-up, immutable servers. The thing holding this technique back was the difficulty in building images, especially when targeting more than one platform. Packer solves this, using your configuration management tool of choice to create images for a number of platforms including AWS, Rackspace, DigitalOcean and even Docker and Vagrant, although we have found the VMWare support to be problematic.
