Some of our allocrunner hooks require a task environment for interpolating values based on the node or allocation. But several of the hooks accept an already-built environment or builder and then keep that in memory. Both of these retain a copy of all the node attributes and allocation metadata, which balloons memory usage until the allocation is GC'd.
While we'd like to look into ways to avoid keeping the allocrunner around entirely (see #25372), for now we can significantly reduce memory usage by creating the task environment on-demand when calling allocrunner methods, rather than persisting it in the allocrunner hooks.
In doing so, we uncover two other bugs:
* The WID manager, the group service hook, and the checks hook have to interpolate services for specific tasks. They mutated a taskenv builder to do so, but each time they mutate the builder, they write to the same environment map. When a group has multiple tasks, it's possible for one task to set an environment variable that would then be interpolated in the service definition for another task if that task did not have that environment variable. Only the service definition interpolation is impacted. This does not leak env vars across running tasks, as each taskrunner has its own builder.
To fix this, we move the `UpdateTask` method off the builder and onto the taskenv as the `WithTask` method. This makes a shallow copy of the taskenv with a deep clone of the environment map used for interpolation, and then overwrites the environment from the task.
* The checks hook interpolates Nomad native service checks only on `Prerun` and not on `Update`. This could cause unexpected deregistration and registration of checks during in-place updates. To fix this, we make sure we interpolate in the `Update` method.
I also bumped into an incorrectly implemented interface in the CSI hook. I've pulled that and some better guardrails out to https://github.com/hashicorp/nomad/pull/25472.
Fixes: https://github.com/hashicorp/nomad/issues/25269
Fixes: https://hashicorp.atlassian.net/browse/NET-12310
Ref: https://github.com/hashicorp/nomad/issues/25372
While working on #25373, I noticed that the CSI hook's `Destroy` method doesn't
match the interface, which means it never gets called. Because this method only
cancels any in-flight CSI requests, the only impact of this bug is that any CSI
RPCs that are in-flight when an alloc is GC'd on the client or a dev agent is
shut down won't be interrupted gracefully.
Fix the interface, but also make static assertions for all the allocrunner hooks
in the production code, so that you can make changes to interfaces and have
compile-time assistance in avoiding mistakes.
Ref: https://github.com/hashicorp/nomad/pull/25373
* client/allocdir: use an interface in place of AllocDir structs
This PR replace *allocdir.AllocDir with allocdir.Interface such that we
may eventually have another implementation of alloc directories. This is
in support of the exec2 driver, which will need an implementation of the
alloc directory incompatibile with the current version.
* use rlock
Some of the context uses in TR hooks are useless (Killed during Stop
never seems meaningful).
None of the hooks are interruptable for graceful shutdown which is
unfortunate and probably needs fixing.
