What version of Docker is my Kubernetes running on?

You can find container runtime and its version using the following:

kubectl get node <node> -o jsonpath="{.status.nodeInfo.containerRuntimeVersion}"

The following kubectl command will show detail information of the nodes in the cluster:

kubectl describe nodes

One instance of a node is shown below:

Name:               node3-virtualbox
Roles:              <none>
Labels:             beta.kubernetes.io/arch=amd64
                    beta.kubernetes.io/os=linux
                    kubernetes.io/hostname=node3-virtualbox
Annotations:        node.alpha.kubernetes.io/ttl=0
                    volumes.kubernetes.io/controller-managed-attach-detach=true
Taints:             <none>
CreationTimestamp:  Tue, 05 Dec 2017 07:01:42 +0100
Conditions:
  Type             Status  LastHeartbeatTime                 LastTransitionTime                Reason                       Message
  ----             ------  -----------------                 ------------------                ------                       -------
  OutOfDisk        False   Tue, 05 Dec 2017 22:52:05 +0100   Tue, 05 Dec 2017 17:08:13 +0100   KubeletHasSufficientDisk     kubelet has sufficient disk space available
  MemoryPressure   False   Tue, 05 Dec 2017 22:52:05 +0100   Tue, 05 Dec 2017 21:08:21 +0100   KubeletHasSufficientMemory   kubelet has sufficient memory available
  DiskPressure     False   Tue, 05 Dec 2017 22:52:05 +0100   Tue, 05 Dec 2017 21:08:21 +0100   KubeletHasNoDiskPressure     kubelet has no disk pressure
  Ready            False   Tue, 05 Dec 2017 22:52:05 +0100   Tue, 05 Dec 2017 21:08:21 +0100   KubeletNotReady              runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:docker: network plugin is not ready: cni config uninitialized
Addresses:
  InternalIP:  10.0.2.15
  Hostname:    node3-virtualbox
Capacity:
 cpu:     1
 memory:  2048268Ki
 pods:    110
Allocatable:
 cpu:     1
 memory:  1945868Ki
 pods:    110
System Info:
 Machine ID:                 9654f9402bfc4042b82b454e323cf46c
 System UUID:                6EBA3E13-624C-4C82-A8EA-24FF86FA6E66
 Boot ID:                    c7217654-8514-482c-9899-f04a3d3ce6d8
 Kernel Version:             4.4.0-101-generic
 OS Image:                   Ubuntu 16.04.1 LTS
 Operating System:           linux
 Architecture:               amd64
 Container Runtime Version:  docker://1.13.1
 Kubelet Version:            v1.8.4
 Kube-Proxy Version:         v1.8.4
ExternalID:                  node3-virtualbox
Non-terminated Pods:         (2 in total)
  Namespace                  Name                CPU Requests  CPU Limits  Memory Requests  Memory Limits
  ---------                  ----                ------------  ----------  ---------------  -------------
  kube-system                kube-proxy-sxp5s    0 (0%)        0 (0%)      0 (0%)           0 (0%)
  kube-system                weave-net-6jf98     20m (2%)      0 (0%)      0 (0%)           0 (0%)
Allocated resources:
  (Total limits may be over 100 percent, i.e., overcommitted.)
  CPU Requests  CPU Limits  Memory Requests  Memory Limits
  ------------  ----------  ---------------  -------------
  20m (2%)      0 (0%)      0 (0%)           0 (0%)
Events:         <none>

The docker version running on the nodes can be found in system info:, for example in above case:

Container Runtime Version: docker://1.13.1