[jira] [Assigned] (MESOS-9116) Flaky processes within POD cause failures of launch nested container due to a bug in `mnt` namespace detection.

["Andrei Budnik (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/MESOS-9116?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Andrei Budnik reassigned MESOS-9116:
------------------------------------

    Assignee: Andrei Budnik

> Flaky processes within POD cause failures of launch nested container due to a bug in `mnt` namespace detection.
> ---------------------------------------------------------------------------------------------------------------
>
>                 Key: MESOS-9116
>                 URL: https://issues.apache.org/jira/browse/MESOS-9116
>             Project: Mesos
>          Issue Type: Task
>          Components: agent, containerization
>            Reporter: Andrei Budnik
>            Assignee: Andrei Budnik
>            Priority: Major
>              Labels: mesosphere
>
> Launch nested container call might fail with the following error:
> {code:java}
> Failed to enter mount namespace: Failed to open '/proc/29473/ns/mnt': No such file or directory
> {code}
> This happens when the containerizer launcher [tries to enter|https://github.com/apache/mesos/blob/077f122d52671412a2ab5d992d535712cc154002/src/slave/containerizer/mesos/launch.cpp#L879-L892] `mnt` namespace using the pid of a terminated process. The pid [was detected|https://github.com/apache/mesos/blob/077f122d52671412a2ab5d992d535712cc154002/src/slave/containerizer/mesos/containerizer.cpp#L1930-L1958] by the agent before spawning the containerizer launcher process because the process was still running.
> The issue can be reproduced using the following test (pseudocode):
> {code:java}
> launchTask("sleep 1000")
> parentContainerId = containerizer.containers().begin()
> outputs = []
> for i in range(10):
>   ContainerId containerId
>   containerId.parent = parentContainerId
>   containerId.id = UUID.random()
>   LAUNCH_NESTED_CONTAINER_SESSION(containerId, "echo echo")
>   response = ATTACH_CONTAINER_OUTPUT(containerId)
>   outputs.append(response.reader)
> for output in outputs:
>   stdout, stderr = getProcessIOData(output)
>   assert("echo" == stdout + stderr){code}
> The given test is stably reproduces the issue after adding `::usleep(500 * 1000);` before returning the result in [`getMountNamespaceTarget()`|https://github.com/apache/mesos/blob/077f122d52671412a2ab5d992d535712cc154002/src/slave/containerizer/mesos/utils.cpp#L89].
> The issue can be reproduced using the test above because `getMountNamespaceTarget()` detects not yet terminated processes from the previous `LAUNCH_NESTED_CONTAINER` calls while attempting to launch a new nested container session.
> Another possible cause might be related to processes stuck in D-state within a POD.
> The flaky process within the POD can end up in D-state (unkillable). This process can be a child of a nested container process, so the agent doesn't know about it. Killing the nested container process doesn't mean that all its child processes, which stuck in D-state, are killed.
> For example, the nested container can be a custom executor which spawns its own tasks which might end up in D-state. Another example is when the containerizer launcher [spawns|https://github.com/apache/mesos/blob/077f122d52671412a2ab5d992d535712cc154002/src/slave/containerizer/mesos/launch.cpp#L755-L768] shell scripts like `mount` during its initialization.
> In that case, the agent might detect a process which should be already terminated, but it still exists because it's in D-state. At the moment when the containerizer launcher is spawned, the stuck process might disappear, so we get the error.



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