A "Layer" is a particular service that forms part of the infrastructure for
a set of applications. Some layers are application servers and others are
pure infrastructure, like MySQL servers or load balancers.
Although the AWS API only has one type called "Layer", it actually has
a number of different "soft" types that each have slightly different
validation rules and extra properties that are packed into the Attributes
map.
To make the validation rule differences explicit in Terraform, and to make
the Terraform structure more closely resemble the OpsWorks UI than its
API, we use a separate resource type per layer type, with the common code
factored out into a shared struct type.
"Stack" is the root concept in OpsWorks, and acts as a container for a number
of different "layers" that each provide some service for an application.
A stack isn't very interesting on its own, but it needs to be created before
any layers can be created.
Here we add an OpsWorks client instance to the central client bundle and
establish a new documentation section, both of which will be fleshed out in
subsequent commits that add some OpsWorks resources.
There are several AWS services that are global in scope and thus need to
be accessed via the us-east-1 endpoints, so we'll make the us-east-1
variant of the config available as a variable we can reuse between multiple
clients as we add support for new services.
A common issue with new resource implementations is not considering parts
of a complex structure that's used inside a set, which causes quirky
behavior.
The schema helper has enough information to provide a default reasonable
implementation of a set function that includes all non-computed attributes
in a deterministic way. Here we implement such a function and use it
when no explicit hashing function is provided.
In order to achieve this we encapsulate the construction of the zero
value for a schema in a new method schema.ZeroValue, which allows us to
put the fallback logic to the new default function in a single spot.
It is no longer valid to use &Set{F: schema.Set} and all uses of that
construct should be replaced with schema.ZeroValue().(*Set) .
Robert Roland