[jira] [Created] (MESOS-5350) Add asynchronous hook for validating docker containerizer tasks

["Joseph Wu (JIRA)" <ji...@apache.org>]

Joseph Wu created MESOS-5350:
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             Summary: Add asynchronous hook for validating docker containerizer tasks
                 Key: MESOS-5350
                 URL: https://issues.apache.org/jira/browse/MESOS-5350
             Project: Mesos
          Issue Type: Improvement
          Components: docker, modules
            Reporter: Joseph Wu
            Assignee: Joseph Wu
            Priority: Minor


It is possible to plug in custom validation logic for the MesosContainerizer via an {{Isolator}} module, but the same is not true of the DockerContainerizer.

Basic logic can be plugged into the DockerContainerizer via {{Hooks}}, but this has some notable differences compared to isolators:
* Hooks are synchronous.
* Modifications to tasks via Hooks have lower priority compared to the task itself.  i.e. If both the {{TaskInfo}} and {{slaveExecutorEnvironmentDecorator}} define the same environment variable, the {{TaskInfo}} wins.
* Hooks have no effect if they fail (short of segfaulting)
i.e. The {{slavePreLaunchDockerHook}} has a return type of {{Try<Nothing>}}:
https://github.com/apache/mesos/blob/628ccd23501078b04fb21eee85060a6226a80ef8/include/mesos/hook.hpp#L90
But the effect of returning an {{Error}} is a log message:
https://github.com/apache/mesos/blob/628ccd23501078b04fb21eee85060a6226a80ef8/src/hook/manager.cpp#L227-L230

We should add a hook to the DockerContainerizer to narrow this gap.  This new hook would:
* Be called at roughly the same place as {{slavePreLaunchDockerHook}}
https://github.com/apache/mesos/blob/628ccd23501078b04fb21eee85060a6226a80ef8/src/slave/containerizer/docker.cpp#L1022
* Return a {{Future}} and require splitting up {{DockerContainerizer::launch}}.
* Prevent a task from launching if it returns a {{Failure}}.



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