Atlas returns an HTTP 409 - Conflict if the pushed state reports the same
Serial number but the checksum of the raw content differs. This can
sometimes happen when Terraform changes state representation internally
between versions in a way that's semantically neutral but affects the JSON
output and therefore the checksum.
Here we detect and handle this situation by ticking the serial and retrying
iff for the previous state and the proposed state:
* the serials match
* the parsed states are Equal (semantically equivalent)
In other words, in this situation Terraform can override Atlas's detected
conflict by asserting that the state it is pushing is indeed correct.
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.
We were only comparing the last element of the module, which meant that
deeply nested modules with the same name but different ancestry had an
undefined sort order, which could cause inconsistencies in state
storage and potentially break remote state MD5 checksumming.
Remote state includes MD5-based checksumming to protect against State
conflicts. This can generate improper conflicts with states that differ
only in their Schema version.
We began to see this issue with
https://github.com/hashicorp/terraform/pull/3470 which changes the
"schema_version" of aws_key_pairs.
* Update init docs to be correct, and provide an example.
* Update remote config docs to provide more details about the Consul
backend and to provide another example.
Paul Hinze