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Automatic merge from submit-queue Prevent kube-proxy from panicing when sysfs is mounted as read-only. Fixes https://github.com/kubernetes/kubernetes/issues/25543. This PR: * Checks the permission of sysfs before setting conntrack hashsize, and returns an error "readOnlySysFSError" if sysfs is readonly. As I know, this is the only place we need write permission to sysfs, CMIIW. * Update a new node condition 'RuntimeUnhealthy' with specific reason, message and hit to the administrator about the remediation. I think this should be an acceptable fix for now. Node problem detector is designed to integrate with different problem daemons, but **the main logic is in the problem detection phase**. After the problem is detected, what node problem detector does is also simply updating a node condition. If we let kube-proxy pass the problem to node problem detector and let node problem detector update the node condition. It looks like an unnecessary hop. The logic in kube-proxy won't be different from this PR, but node problem detector will have to open an unsafe door to other pods because the lack of authentication mechanism. It is a bit hard to test this PR, because we don't really have a bad docker in hand. I can only manually test it: * If I manually change the code to let it return `"readOnlySysFSError`, the node condition will be updated: ``` NetworkUnavailable False Mon, 01 Jan 0001 00:00:00 +0000 Fri, 08 Jul 2016 01:36:41 -0700 RouteCreated RouteController created a route OutOfDisk False Fri, 08 Jul 2016 01:37:36 -0700 Fri, 08 Jul 2016 01:34:49 -0700 KubeletHasSufficientDisk kubelet has sufficient disk space available MemoryPressure False Fri, 08 Jul 2016 01:37:36 -0700 Fri, 08 Jul 2016 01:34:49 -0700 KubeletHasSufficientMemory kubelet has sufficient memory available Ready True Fri, 08 Jul 2016 01:37:36 -0700 Fri, 08 Jul 2016 01:35:26 -0700 KubeletReady kubelet is posting ready status. WARNING: CPU hardcapping unsupported RuntimeUnhealthy True Fri, 08 Jul 2016 01:35:31 -0700 Fri, 08 Jul 2016 01:35:31 -0700 ReadOnlySysFS Docker unexpectedly mounts sysfs as read-only for privileged container (docker issue #24000). This causes the critical system components of Kubernetes not properly working. To remedy this please restart the docker daemon. KernelDeadlock False Fri, 08 Jul 2016 01:37:39 -0700 Fri, 08 Jul 2016 01:35:34 -0700 KernelHasNoDeadlock kernel has no deadlock Addresses: 10.240.0.3,104.155.176.101 ``` * If not, the node condition `RuntimeUnhealthy` won't appear. * If I run the permission checking code in a unprivileged container, it did return `readOnlySysFSError`. I'm not sure whether we want to mark the node as `Unscheduable` when this happened, which only needs few lines change. I can do that if we think we should. I'll add some unit test if we think this fix is acceptable. /cc @bprashanth @dchen1107 @matchstick @thockin @alex-mohr Mark P1 to match the original issue. []()