mirror of https://github.com/pulumi/pulumi.git
bac11495cd
As we discovered when removing aliases from the state entirely, the snapshotter needs to be alias-aware so that it can fix up references to resources that were aliased. After a resource operation finishes, the snapshotter needs to write out a new copy of the snapshot. However, at the time we write the snapshot, there may be resources that have not yet been registered that refer to the just-registered resources by a different URN due to aliasing. Those references need to be fixed up prior to writing the snapshot in order to preserve the snapshot's integrity (in particular, the property that all URNs refer to resources that exist in the snapshot). For example, consider the following simple dependency graph: A <-- B. When that graph is serialized, B will contain a reference to A in its dependency list. Let the next run of the program produces the graph A' <-- B where A' is aliased to A. After A' is registered, the snapshotter needs to write a snapshot that contains its state, but B must also be updated so it references A' instead of A, which will no longer be in the snapshot. These changes take advantage of the fact that although a resource can provide multiple aliases, it can only ever resolve those aliases to a single resource in the existing state. Therefore, at the time the statefile is fixed up, each resource in the statefile could only have been aliased to a single old resource, and it is sufficient to store only the URN of the chosen resource rather than all possible aliases. In addition to preserving the ability to fix up references to aliased resources, retaining the chosen alias allows the history of a logical resource to be followed across aliases. |
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