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DescriptionStefan Schimanski
2016-10-19 09:06:29 UTC
Description of problem:
Running a container with sysctls which is rejected by the kernel gives a "System error: could not synchronise with container process." error message from the /container/<id>/start API call (https://docs.docker.com/engine/reference/api/docker_remote_api_v1.24/#/start-a-container):
docker run -it --sysctl=kernel.shm_rmid_forced=hello ubuntu /bin/bash -c "sysctl kernel.shm_rmid_forced" sttts-sni
write /proc/sys/kernel/shm_rmid_forced: invalid argument
docker: Error response from daemon: Cannot start container 2424aea6711a7335b5ea1c171f544a39862fa2886240685b2b73a695a655487c: [9] System error: could not synchronise with container process.
The actual sysctl error shown above is from the container logs, not part of the error message of the API call. The later is too generic. Parsing logs in order to react properly on the error is not an option.
Compare this with e.g. the --user flags:
docker run -it -u foo ubuntu /bin/bash -c "sysctl kernel.shm_rmid_forced" sttts-sni
unable to find user foo: no matching entries in passwd file
docker: Error response from daemon: Cannot start container 7d63df9760ff964bd4a99e512c8d53777e8b59577959f47de8ad9285482fbe21: [9] System error: unable to find user foo: no matching entries in passwd file.
Here the error message is explicit.
Why is this relevant?
The Kubernetes kubelet must be able to react on sysctl errors properly, i.e. without restarting the container again and again. Instead the error should be reported to the user as an pod event. For that a proper, well known and stable error message is required. Parsing the logs for arbitrary plain text message is not a viable option here as such a message might change any time with future Docker versions or kernels.
Version-Release number of selected component (if applicable):
v1.12
Expected results:
docker run -it --sysctl=kernel.shm_rmid_forced=hello ubuntu /bin/bash -c "sysctl kernel.shm_rmid_forced" sttts-sni
write /proc/sys/kernel/shm_rmid_forced: invalid argument
docker: Error response from daemon: Cannot start container 2424aea6711a7335b5ea1c171f544a39862fa2886240685b2b73a695a655487c: [9] System error: cannot write /proc/sys/kernel/shm_rmid_forced: invalid argument
Comment 1Stefan Schimanski
2016-10-31 13:16:21 UTC