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Actions Required
================
* Long-term solution to 'rogue' interfaces is unclear. May require update to OpenShift 3.9 or later.
However, proposed work-around should do unless execution rate grows significantly.
* All other problems found in logs can be ignored.
Rogue network interfaces on OpenVSwitch bridge
==============================================
Sometimes OpenShift fails to clean-up after terminated pod properly. The actual reason is unclear, but
severity of the problem is increased if extreme amount of images is presented in local Docker storage.
Several thousands is defenitively intensifies this problem.
* The issue is discussed here:
https://bugzilla.redhat.com/show_bug.cgi?id=1518684
* And can be determined by looking into:
ovs-vsctl show
Problems:
* As number of rogue interfaces grow, it start to have impact on performance. Operations with
ovs slows down and at some point the pods schedulled to the affected node fail to start due to
timeouts. This is indicated in 'oc describe' as: 'failed to create pod sandbox'
* With time, the new rogue interfaces are created faster and faster. At some point, it really
slow downs system and causes pod failures (if many pods are re-scheduled in paralllel) even
if not so many rogue interfaces still present
* Even if not failed, it takes several minutes to schedule the pod on the affected nodes.
Cause:
* Unclear, but it seems periodic ADEI cron jobs causes the issue if many images are present
in docker.
* Could be related to 'container kill failed' problem explained in the section bellow.
Cannot kill container ###: rpc error: code = 2 desc = no such process
Solutions:
* According to RedHat the temporal solution is to reboot affected node (just temporarily reduces the rate how
often the new spurious interfaces appear, but not preventing the problem completely in my case). The problem
should go away, but may re-apper after a while.
* The simplest work-around is to just remove rogue interface. They will be re-created, but performance
problems only starts after hundreds accumulate.
ovs-vsctl del-port br0 <iface>
* It seems helpful to purge unused docker images to reduce the rate of interface apperance.
Status:
* Cron job is installed which cleans rogue interfaces as they number hits 25.
Hanged pods
===========
POD processes may stuck. Normally, such processes will be detected using 'liveliness' probe and will be
restarted by OpenShift if necessary. However, ocasionally processes may stuck in syscalls (such processes
are marked with 'D' in ps). These processes can't be killed with SIGKILL and OpenShift will not be able
to terminate them leaving indefinitely in 'Terminating' status.
Problems:
* Pods stuck in 'Terminating' status preventing start of new replicas. In case of 'jobs', large number
of 'Terminating' pods could overload OpenShift controllers.
Cause:
* One reason are the spurious locks on the GlusterFS file system. On CentOS 7, it impossible to interrupt
process waiting for the lock initiated by blocking 'flock' call. It gets stuck in a syscall and is indicated
by state 'D' in the ps output. Sometimes, GlusterFS may kept files locked despite that processes holding these
locks have already exited/crashed. I am not sure about exact conditions when this happens, but it seems for
instance the crashed Docker daemon may cause effect if some of the running containers were holding locks on
GFS at the moment of crash.
- We can verify if this is the case by checking if process associated with the problematic pod is stuck in
state 'D' and by analyzing its backtrace (/proc/<pid>/stack).
Solutions:
* Avoid blocking flock on GlusterFS. Use polling with sleep instead. To release already stuck pods, we need
to find and destroy problematic locks. GlusterFS allows to debug locks using 'statedump', check GlusterFS
documentation for details. While there is also mechanism to clean such locks. It is not always working.
Alternative is to remove locked files AND keep them removed for a while until all blocked 'flock' syscalls
are released.
Hanged MySQL connection
=======================
Stale MySQL locks may prevent new clients connecting to certain tables in MySQL database.
Problems:
* The problem may affect either only clients trying to obtain 'write' access or for all usage patterns. In the first case,
it will cause ADEI 'caching' threads to hang indefinitely and 'maintain' threads will be terminated after specified timeout
leaving administrative scripts un-processed.
Cause:
* For whatever reason, some crashed clients may preserve the locks. I believe it could also be caused by
crashed 'docker' daemon as one possibel reason. The problem can be found bt executing 'SHOW PROCESSLIST'
on MySQL server. More diagnostic possibilities are discussed in MySQL notes.
Solutions;
* Normally, restarting MySQL pod should be enough.
Orphaning / pod termination problems in the logs
================================================
There is several classes of problems reported with unknow reprecursions in the system log. Currently, I
don't see any negative side effects except some of these issues may trigger "rogue interfaces" problem.
! container kill failed because of 'container not found' or 'no such process': Cannot kill container ###: rpc error: code = 2 desc = no such process"
Despite the errror, the containers are actually killed and pods destroyed. However, this error likely triggers
problem with rogue interfaces staying on the OpenVSwitch bridge.
Scenario:
* happens with short-living containers
- containerd: unable to save f7c3e6c02cdbb951670bc7ff925ddd7efd75a3bb5ed60669d4b182e5337dec23:d5b9394468235f7c9caca8ad4d97e7064cc49cd59cadd155eceae84545dc472a starttime: read /proc/81994/stat: no such process
containerd: f7c3e6c02cdbb951670bc7ff925ddd7efd75a3bb5ed60669d4b182e5337dec23:d5b9394468235f7c9caca8ad4d97e7064cc49cd59cadd155eceae84545dc472a (pid 81994) has become an orphan, killing it
Scenario:
This happens every couple of minutes and attributed to perfectely alive and running pods.
* For instance, ipekatrin1 was complaining some ADEI pod.
* After I removed this pod, it immidiately started complaining on 'glusterfs' replica.
* If 'glusterfs' pod re-created, the problem persist.
* It seems only a single pod is affected at each given moment (at least this was always true
on ipekatrin1 & ipekatrin2 while I was researching the problem)
Relations:
* This problem is not aligned with the next 'container not found' problem. One happens with short-living containers which
actually get destroyed. This one is triggered for persistent container which keep going. And in fact this problem is triggered
significantly more frequently.
Cause:
* Seems related to docker health checks due to a bug in docker 1.12* which is resolved in 1.13.0rc2
https://github.com/moby/moby/issues/28336
Problems:
* It seems only extensive logging, according to the discussion in the issue
Solution: Ignore for now
* docker-1.13 had some problems with groups (I don't remember exactly) and it was decided to not run it with current version of KaaS.
* Only update docker after extensive testing on the development cluster or not at all.
- W0625 03:49:34.231471 36511 docker_sandbox.go:337] failed to read pod IP from plugin/docker: NetworkPlugin cni failed on the status hook for pod "...": Unexpected command output nsenter: cannot open /proc/63586/ns/net: No such file or directory
- W0630 21:40:20.978177 5552 docker_sandbox.go:337] failed to read pod IP from plugin/docker: NetworkPlugin cni failed on the status hook for pod "...": CNI failed to retrieve network namespace path: Cannot find network namespace for the terminated container "..."
Scenario:
* It seems can be ignored, see RH bug.
* Happens with short-living containers (adei cron jobs)
Relations:
* This is also not aligned with 'container not found'. The time in logs differ significantly.
* It is also not aligned with 'orphan' problem.
Cause:
? https://bugzilla.redhat.com/show_bug.cgi?id=1434950
- E0630 14:05:40.304042 5552 glusterfs.go:148] glusterfs: failed to get endpoints adei-cfg[an empty namespace may not be set when a resource name is provided]
E0630 14:05:40.304062 5552 reconciler.go:367] Could not construct volume information: MountVolume.NewMounter failed for volume "kubernetes.io/glusterfs/4
I guess some configuration issue.... Probably can be ignored...
Scenario:
* Reported on long running pods with persistent volumes (katrin, adai-db)
* Also seems an unrelated set of the problems.
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