This introduces the concept of "backend aliases", which are alternative
names that can be used to refer to a given backend.
Each backend type has one canonical name and zero or more alias names. The
"backend" block in the root module can specify either a canonical backend
type or an alias, but internally OpenTofu will always track the backend
type using its canonical name.
In particular, the following are all true when the configuration specifies
an alias instead of a canonical backend type:
- The "tofu init" output includes a brief extra message saying which
backend type OpenTofu actually used, because that is the name that we'd
prioritize in our documentation and so an operator can use the canonical
type to find the relevant docs when needed.
- The .terraform/terraform.tfstate file that tracks the working directory's
currently-initialized backend settings always uses the canonical backend
type, and so it's possible to freely switch between aliases and canonical
without "tofu init" thinking that a state migration might be needed.
- Plan files similarly use the canonical backend type to track which
backend was active when the plan was created, which doesn't have any
significant user-facing purpose, but is consistent with the previous
point since the settings in the plan file effectively substitute for
the .terraform/terraform.tfstate file when applying a saved plan.
- The terraform_remote_state data source in the provider
terraform.io/builtin/terraform accepts both canonical and alias in its
backend type argument, treating both as equivalent for the purpose of
fetching the state snapshot for the configured workspace.
The primary motivation for this new facility is to allow the planned
"oracle_oci" backend to have an alias "oci" to allow writing configurations
that are cross-compatible with HashiCorp Terraform, since that software
has chosen to have unqualified OCI mean Oracle's system, whereas OpenTofu
has previously established that unqualified OCI means "Open Container
Initiative" in our ecosystem.
In particular, this design makes it possible in principle to bring an
existing Terraform configuration specifying backend "oci" over to OpenTofu
without modifications, and then to optionally switch it to specifying
backend "oracle-oci" at a later time without a spurious prompt to migrate
state snapshots to the same physical location where they are already
stored.
This commit doesn't actually introduce any aliases and therefore doesn't
have any tests for the new mechanism because our backend system uses a
global table that isn't friendly to mocking for testing purposes. I've
tested this manually using a placeholder alias to have confidence that it
works, and I expect that a subsequent commit introducing the new
"oracle_oci" backend will also introduce its "oci" alias and will include
tests that cover use of the alias and migration from the alias to the
canonical name and vice-versa.
Signed-off-by: Martin Atkins <mart@degeneration.co.uk>
This allows us to remove the manual replace directives
github.com/dgrijalva/jwt-go and google.golang.org/grpc, so that we can
remove the CVE warnings and update the grpc packages.
While the etcdv3 backend is also marked as deprecated, the changes here
are done in a manner to keep that backend working for the time being.
This is part of a general effort to move all of Terraform's non-library
package surface under internal in order to reinforce that these are for
internal use within Terraform only.
If you were previously importing packages under this prefix into an
external codebase, you could pin to an earlier release tag as an interim
solution until you've make a plan to achieve the same functionality some
other way.
