These new functions allow Terraform to be used for network address space
planning tasks, and make it easier to produce reusable modules that
contain or depend on network infrastructure.
For example:
- cidrsubnet allows an aws_subnet to derive its
CIDR prefix from its parent aws_vpc.
- cidrhost allows a fixed IP address for a resource to be assigned within
an address range defined elsewhere.
- cidrnetmask provides the dotted-decimal form of a prefix length that is
accepted by some systems such as routing tables and static network
interface configuration files.
The bulk of the work here is done by an external library I authored called
go-cidr. It is MIT licensed and was implemented primarily for the purpose
of using it within Terraform. It has its own unit tests and so the unit
tests within this change focus on simple success cases and on the correct
handling of the various error cases.
There isn't any precedent for abbreviating words in the interpolation
function names, and it may not be clear to all users what "enc" and "dec"
are short for, so instead we'll prefer to spell out the whole words for
improved readability.
As reported in #2782, the math operations, specifically subtraction,
can cause unexpected behavior when resource or variable names use hyphens.
I added clarification about using spaces with math operators as well as
which operations are available.
formatlist distributes formatting over lists.
See the docs for details.
As a colleague commented:
"It happens all the time that we want a set of
outputs, but in a slightly different way than
just simple joining or concatting."
formatlist (combined with join)
makes it easy to satisfy those needs.
When the `prevent_destroy` flag is set on a resource, any plan that
would destroy that resource instead returns an error. This has the
effect of preventing the resource from being unexpectedly destroyed by
Terraform until the flag is removed from the config.
The Terraform configuration syntax defines what arrays are.
Use the word array consistently throughout the documentation
instead of list.
The corresponding JSON datatype is called array as well, and
since the Terraform configuration syntax is interoperable with
JSON it makes sense to use the term array to describe them.
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