A stack is a connected set of resources within an OpsWorks environment. We would create stacks to logically group together resources belonging to a certain application or another logical grouping. We would typically allow stacks to be provisioned and managed as a whole unit, but we can logically separate the functional parts of a stack into layers. A stack is required to have at least one layer.
An example of a stack that would manage a three-tier application would contain the following:
- A load balancer server recipe or manifest
- A web frontend server recipe or manifest
- A database server recipe or manifest
We would usually group the applications into stacks according to the purpose they serve, so we would typically find a development stack, a testing stack, and staging and production stacks being managed for one application within an OpsWorks environment.
We can also use stacks when performing blue/green deployments to update our application. Any existing stack can easily be cloned to a new stack, and a DNS switch-over can be performed to swap the environment URLs from the blue to the green environment, as represented in the following diagram:
