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By now you should know what Packer does and what the benefits of image creation are. In this section, we'll enumerate some of the use cases for Packer. Note that this is not an exhaustive list by any means. There are definitely use cases for Packer not listed here. This list is just meant to give you an idea of how Packer may improve your processes.
Packer is lightweight, portable, and command-line driven. This makes it the perfect tool to put in the middle of your continuous delivery pipeline. Packer can be used to generate new machine images for multiple platforms on every change to Chef/Puppet.
As part of this pipeline, the newly created images can then be launched and tested, verifying the infrastructure changes work. If the tests pass, you can be confident that the image will work when deployed. This brings a new level of stability and testability to infrastructure changes.
Packer helps keep development, staging, and production as similar as possible. Packer can be used to generate images for multiple platforms at the same time. So if you use AWS for production and VMware (perhaps with Vagrant) for development, you can generate both an AMI and a VMware machine using Packer at the same time from the same template.
Mix this in with the continuous delivery use case above, and you have a pretty slick system for consistent work environments from development all the way through to production.
Since Packer creates consistent images for multiple platforms in parallel, it is perfect for creating appliances and disposable product demos. As your software changes, you can automatically create appliances with the software pre-installed. Potential users can then get started with your software by deploying it to the environment of their choice.
Packaging up software with complex requirements has never been so easy. Or enjoyable, if you ask me.