Both differing serials and lineage protections should be bypassed
with the -force flag (in addition to resources).
Compared to other backends we aren’t just shipping over the state
bytes in a simple payload during the persistence phase of the push
command and the force flag added to the Go TFE client needs to be
specified at that time.
To prevent changing every method signature of PersistState of the
remote client I added an optional interface that provides a hook
to flag the Client as operating in a force push context. Changing
the method signature would be more explicit at the cost of not
being used anywhere else currently or the optional interface pattern
could be applied to the state itself so it could be upgraded to
support PersistState(force bool) only when needed.
Prior to this only the resources of the state were checked for
changes not the lineage or the serial. To bring this in line with
documented behavior noted above those attributes also have a “read”
counterpart just like state has. These are now checked along with
state to determine if the state as a whole is unchanged.
Tests were altered to table driven test format and testing was
expanded to include WriteStateForMigration and its interaction
with a ClientForcePusher type.
We only persist a new state if the actual state contents have
changed. This test demonstrates that behavior by calling write
and persist methods when either the lineage or serial have changed.
Previously we would write to the backend for every call to PersistState,
even if nothing changed since the last write, but update the serial only
if the state had changed.
The Terraform Cloud & Enterprise state storage have a simple safety check
that any future write with an already-used lineage and serial must be
byte-for-byte identical. StatesMarshalEqual is intended to detect that,
but it only actually detects changes the state itself, and not changes
to the snapshot metadata.
Because we write the current Terraform version into the snapshot metadata
during serialization, we'd previously have an issue where if the first
state write after upgrading Terraform to a new version happened to change
nothing about the state content then we'd write a new snapshot that
differed only by Terraform version, and Terraform Cloud/Enterprise would
then reject it.
The snapshot header is discarded immediately after decoding, so we can't
use information from it when deciding whether to increment the serial.
The next best thing is to skip sending no-op snapshot updates to the state
client in the first place.
These writes are unnecessary anyway, and state storage owners have asked
us in the past to elide these to avoid generating noise in their version
logs, so we'll also finally meet those requests as a nice side-effect of
this change.
We didn't previously have tests for the full flow of retrieving and then
successively updating persisted state snapshots, so this includes a test
which covers that logic and includes an assertion that a no-op update does
not get written to the state client.
These statemgr interfaces are the new names for the older interfaces in
the "state" package. These types alias each other so it doesn't really
matter which we use, but the "state" package is deprecated and we intend
to eventually remove it, so this is a further step in that direction.
Lee Trout