Now that you understand the rationale for building a custom ECS container instance image, let's introduce a tool called Packer, which allows you to build machine images for a wide variety of platforms, including AWS.
Packer is an open source tool created by HashiCorp, which you can find out more about at https://www.packer.io/. Packer can build machine images for a wide variety of target platforms, however in this chapter we will only focus on building Amazon Machine Images.