The driver manager is modeled after the device manager and is started by the client.
It's responsible for handling driver lifecycle and reattachment state, as well as
processing the incomming fingerprint and task events from each driver. The mananger
exposes a method for registering event handlers for task events that is used by the
task runner to update the server when a task has been updated with an event.
Since driver fingerprinting has been implemented by the driver manager, it is no
longer needed in the fingerprint mananger and has been removed.
The RestartCount is not really suitable for use as a source of
uniqueness within task invocations as it is not monotonic, and interacts
with the restart stanza in a users config, so conflates restarts due to
task failures, with restarts due to enviromental changes, such as consul
template or vault secrets changing.
Here we instead use a substring from a uuid, which is more random than
we strictly need, but is nicer than rolling our own random string
generator here.
This creates a new buffered channel and goroutine on the allocrunner for
serializing updates to allocations. This allows us to take updates off
the routine that is used from processing updates from the server,
without having complicated machinery for tracking update lifetimes, or
other external synchronization.
This results in a nice performance improvement and signficantly better
throughput on batch changes such as preempting a large number of jobs
for a larger placement.
This commit reduces the locking required to shutdown or destroy
allocrunners, and allows parallel shutdown and destroy of allocrunners during
shutdown.
When starting an allocation that is preempting other allocs, we create a
new group allocation watcher, and then wait for the allocations to
terminate in the allocation PreRun hooks.
If there's no preempted allocations, then we simply provide a
NoopAllocWatcher.
As part of deprecating legacy drivers, we're moving the env package to a
new drivers/shared tree, as it is used by the modern docker and rkt
driver packages, and is useful for 3rd party plugins.
Looking at NewTaskRunner I'm unsure whether TaskRunner.TaskResources
(from which req.TaskResources is set) is intended to be nil at times or
if the TODO in NewTaskRunner is intended to ensure it is always non-nil.
Alex Dadgar