applying a plan should use the refreshed state #15423
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When applying a plan, a copy of the plan's state is initially persisted to state storage, which may in turn increment the serial number. The apply operation stil uses the state stored in the plan, which may have a lower serial number. Now we no longer use the plan state when building the apply context, but still perform a sanity check to ensure that the state be used is equivalent.
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Since this is something we need to solve urgently and this is only minor changes from @jbardin's original I'm going to merge this without explicit review; both James and I have had our eyes on it and discussed it, even though that's not formally recognized here in Github. |
apparentlymart
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Previously we relied on a constellation of coincidences for everything to work out correctly with state serials. In particular, callers needed to be very careful about mutating states (or not) because many different bits of code shared pointers to the same objects. Here we move to a model where all of the state managers always use distinct instances of state, copied when WriteState is called. This means that they are truly a snapshot of the state as it was at that call, even if the caller goes on mutating the state that was passed. We also adjust the handling of serials so that the state managers ignore any serials in incoming states and instead just treat each Persist as the next version after what was most recently Refreshed. (An exception exists for when nothing has been refreshed, e.g. because we are writing a state to a location for the first time. In that case we _do_ trust the caller, since the given state is either a new state or it's a copy of something we're migrating from elsewhere with its state and lineage intact.) The intent here is to allow the rest of Terraform to not worry about serials and state identity, and instead just treat the state as a mutable structure. We'll just snapshot it occasionally, when WriteState is called, and deal with serials _only_ at persist time. This is intended as a more robust version of #15423, which was a quick hotfix to an issue that resulted from our previous slopping handling of state serials but arguably makes the problem worse by depending on an additional coincidental behavior of the local backend's apply implementation.
apparentlymart
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Previously we relied on a constellation of coincidences for everything to work out correctly with state serials. In particular, callers needed to be very careful about mutating states (or not) because many different bits of code shared pointers to the same objects. Here we move to a model where all of the state managers always use distinct instances of state, copied when WriteState is called. This means that they are truly a snapshot of the state as it was at that call, even if the caller goes on mutating the state that was passed. We also adjust the handling of serials so that the state managers ignore any serials in incoming states and instead just treat each Persist as the next version after what was most recently Refreshed. (An exception exists for when nothing has been refreshed, e.g. because we are writing a state to a location for the first time. In that case we _do_ trust the caller, since the given state is either a new state or it's a copy of something we're migrating from elsewhere with its state and lineage intact.) The intent here is to allow the rest of Terraform to not worry about serials and state identity, and instead just treat the state as a mutable structure. We'll just snapshot it occasionally, when WriteState is called, and deal with serials _only_ at persist time. This is intended as a more robust version of #15423, which was a quick hotfix to an issue that resulted from our previous slopping handling of state serials but arguably makes the problem worse by depending on an additional coincidental behavior of the local backend's apply implementation.
apparentlymart
added a commit
that referenced
this pull request
Jul 5, 2017
Previously we relied on a constellation of coincidences for everything to work out correctly with state serials. In particular, callers needed to be very careful about mutating states (or not) because many different bits of code shared pointers to the same objects. Here we move to a model where all of the state managers always use distinct instances of state, copied when WriteState is called. This means that they are truly a snapshot of the state as it was at that call, even if the caller goes on mutating the state that was passed. We also adjust the handling of serials so that the state managers ignore any serials in incoming states and instead just treat each Persist as the next version after what was most recently Refreshed. (An exception exists for when nothing has been refreshed, e.g. because we are writing a state to a location for the first time. In that case we _do_ trust the caller, since the given state is either a new state or it's a copy of something we're migrating from elsewhere with its state and lineage intact.) The intent here is to allow the rest of Terraform to not worry about serials and state identity, and instead just treat the state as a mutable structure. We'll just snapshot it occasionally, when WriteState is called, and deal with serials _only_ at persist time. This is intended as a more robust version of #15423, which was a quick hotfix to an issue that resulted from our previous slopping handling of state serials but arguably makes the problem worse by depending on an additional coincidental behavior of the local backend's apply implementation.
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I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues. If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further. |
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When applying a plan, a copy of the plan's state is initially persisted to state storage, which may in turn increment the serial number. The apply operation stil uses the state stored in the plan, which may have a lower serial number.
Now we no longer use the plan state when building the apply context, but still perform a sanity check to ensure that the state be used is equivalent.
This is the same as #15421, but adapted to apply to the 0.9 line so we can release it before 0.10.0 final.