Fixes#10440
This updates the behavior of "apply" resources to depend on the
destroy versions of their dependencies.
We make an exception to this behavior when the "apply" resource is CBD.
This is odd and not 100% correct, but it mimics the behavior of the
legacy graphs and avoids us having to do major core work to support the
100% correct solution.
I'll explain this in examples...
Given the following configuration:
resource "null_resource" "a" {
count = "${var.count}"
}
resource "null_resource" "b" {
triggers { key = "${join(",", null_resource.a.*.id)}" }
}
Assume we've successfully created this configuration with count = 2.
When going from count = 2 to count = 1, `null_resource.b` should wait
for `null_resource.a.1` to destroy.
If it doesn't, then it is a race: depending when we interpolate the
`triggers.key` attribute of `null_resource.b`, we may get 1 value or 2.
If `null_resource.a.1` is destroyed, we'll get 1. Otherwise, we'll get
2. This was the root cause of #10440
In the legacy graphs, `null_resource.b` would depend on the destruction
of any `null_resource.a` (orphans, tainted, anything!). This would
ensure proper ordering. We mimic that behavior here.
The difference is CBD. If `null_resource.b` has CBD enabled, then the
ordering **in the legacy graph** becomes:
1. null_resource.b (create)
2. null_resource.b (destroy)
3. null_resource.a (destroy)
In this case, the update would always have 2 values for `triggers.key`,
even though we were destroying a resource later! This scenario required
two `terraform apply` operations.
This is what the CBD check is for in this PR. We do this to mimic the
behavior of the legacy graph.
The correct solution to do one day is to allow splat references
(`null_resource.a.*.id`) to happen in parallel and only read up to to
the `count` amount in the state. This requires some fairly significant
work close to the 0.8 release date, so we can defer this to later and
adopt the 0.7.x behavior for now.
Init should only _add_ values, not remove them.
During graph execution, there are steps that expect that a state isn't
being actively pruned out from under it. Namely: writing deposed states.
Writing deposed states has no way to handle if a state changes
underneath it because the only way to uniquely identify a deposed state
is its index in the deposed array. When destroying deposed resources, we
set the value to `<nil>`. If the array is pruned before the next deposed
destroy, then the indexes have changed, and this can cause a crash.
This PR does the following (with more details below):
* `init()` no longer prunes.
* `ReadState()` always prunes before returning. I can't think of a
scenario where this is unsafe since generally we can always START
from a pruned state, its just causing problems to prune
mid-execution.
* Exported State APIs updated to be robust against nil ModuleStates.
Instead, I think we should adopt the following semantics for init/prune
in our structures that support it (Diff, for example). By having
consistent semantics around these functions, we can avoid this in the
future and have set expectations working with them.
* `init()` (in anything) will only ever be additive, and won't change
ordering or existing values. It won't remove values.
* `prune()` is destructive, expectedly.
* Functions on a structure must not assume a pruned structure 100% of
the time. They must be robust to handle nils. This is especially
important because in many cases values such as `Modules` in state
are exported so end users can simply modify them outside of the
exported APIs.
This PR may expose us to unknown crashes but I've tried to cover our
cases in exposed APIs by checking for nil.
Fixes#10439
When a CBD resource depends on a non-CBD resource, the non-CBD resource
is auto-promoted to CBD. This was done in
cf3a259. This PR makes it so that we
also set the config CBD to true. This causes the proper runtime
execution behavior to occur where we depose state and so on.
So in addition to simple graph edge tricks we also treat the non-CBD
resources as CBD resources.
Mitchell Hashimoto