Fixes#2478#2474#1995#2294
The new client only handles agent and task service advertisement. Server
discovery is mostly unchanged.
The Nomad client agent now handles all Consul operations instead of the
executor handling task related operations. When upgrading from an
earlier version of Nomad existing executors will be told to deregister
from Consul so that the Nomad agent can re-register the task's services
and checks.
Drivers - other than qemu - now support an Exec method for executing
abritrary commands in a task's environment. This is used to implement
script checks.
Interfaces are used extensively to avoid interacting with Consul in
tests that don't assert any Consul related behavior.
This PR fixes token revocation and adds tests to make sure it is
working. The 0.5.6 RC1's token revocation does not work becasue the
token's value is captured at the instantiation of the deferred
stoprenewal statement rather than its exectution.
This PR fixes an issue that is hit when running templates with restart
mode in which the client could panic when the handle is not running.
Fixes https://github.com/hashicorp/nomad/issues/2479
This PR fixes two issues:
1) A close of a nil stopCollection channel when restoring and prestart
fails. The failure will cause the killCh to be triggered which will
close collection before it has been initialized.
2) Fixes a deadlock in which the handleWaitCh is never triggered since
it is not initialized when there is an error in prestart and the killCh
is triggered.
Both fixes are by maintaining the loop invariant that the two channels
are valid after there is a handle.
This *might* be a fix for #2295 -- I've been unable to reproduce the
bug. However, this guard seems wise regardless. I should never be
overwriting an intialized created resources with a nil.
Cleanup can be used for cleaning up resources created by drivers to run
a task. Initially the Docker driver is the only user (to remove
downloaded images).
The Driver.Prestart method currently does very little but lays the
foundation for where lifecycle plugins can interleave execution _after_
task environment setup but _before_ the task starts.
Currently Prestart does two things:
* Any driver specific task environment building
* Download Docker images
This change also attaches a TaskEvent emitter to Drivers, so they can
emit events during task initialization.
