Thse changes make a subtle but critical adjustment to the process the
Pulumi engine uses to determine whether or not a difference exists
between a resource's actual and desired states, and adjusts the way this
difference is calculated and displayed accordingly.
Today, the Pulumi engine get the first chance to decide whether or not
there is a difference between a resource's actual and desired states. It
does this by comparing the current set of inputs for a resource (i.e.
the inputs from the running Pulumi program) with the last set of inputs
used to update the resource. If there is no difference between the old
and new inputs, the engine decides that no change is necessary without
consulting the resource's provider. Only if there are changes does the
engine consult the resource's provider for more information about the
difference. This can be problematic for a number of reasons:
- Not all providers do input-input comparison; some do input-state
comparison
- Not all providers are able to update the last deployed set of inputs
when performing a refresh
- Some providers--either intentionally or due to bugs--may see changes
in resources whose inputs have not changed
All of these situations are confusing at the very least, and the first
is problematic with respect to correctness. Furthermore, the display
code only renders diffs it observes rather than rendering the diffs
observed by the provider, which can obscure the actual changes detected
at runtime.
These changes address both of these issues:
- Rather than comparing the current inputs against the last inputs
before calling a resource provider's Diff function, the engine calls
the Diff function in all cases.
- Providers may now return a list of properties that differ between the
requested and actual state and the way in which they differ. This
information will then be used by the CLI to render the diff
appropriately. A provider may also indicate that a particular diff is
between old and new inputs rather than old state and new inputs.
Fixes#2453.
6e5c4a38d8