Kubectl Dispatcher

The Version Skew Problem

A kubectl executable and an API Server it is communicating with might not be at the same version. Kubernetes dictates that kubectl must correctly communicate with an API Server that is plus or minus one version away from the kubectl version. For example, kubectl version 1.11 is guaranteed to correctly communicate with a 1.10, 1.11, and 1.12 Kubernetes cluster. Outside of this support window, there are no correctness guarantees.

The Kubectl Dispatcher Solution

The kubectl dispatcher addresses this version skew problem by executing the exact kubectl version which matches the API Server version. The kubectl dispatcher is a wrapper which retrieves the server version from a cluster, and delegates to the appropriate kubectl version. For example, if a user is configured to talk to their Kubernetes cluster that is version 1.10.3-gke, then the dispatcher will execute "kubectl.1.10" (in the same directory as the the dispatcher) passing the arguments and environment passed to the dispatcher.

IMPORTANT: Versioned kubectl binaries that are dispatched to, MUST be in the same directory as the dispatcher. Versioned kubectl binaries MUST follow the naming convention: kubectl.<major>.<minor>. Example: kubectl.1.12.

NOTE: versioned kubectl filenames must NOT start with "kubectl-", since that is reserved for plugins. Therefore, we prefix versioned kubectl filenames with "kubectl.". Example: "kubectl.1.12"

• Build
• Test
• Run

Build

$ go build cmd/kubectl/kubectl.go

Test

Unit Tests

$ go test -v ./pkg/...

End-to-End Tests

Add the dispatcher to the current directory.

$ cp DISPATCHER_BINARY $(pwd)/kubectl
$ chmod u+x kubectl

Add all the versioned kubectl binaries in the same directory as the kubectl dispatcher.Do this for every cluster version tested. Example for a 1.11 cluster:

$ wget https://storage.googleapis.com/kubernetes-release/release/v1.11.7/bin/linux/amd64/kubectl
$ mv kubectl clibin/kubectl.1.11
$ chmod +x clibin/kubectl.1.11

Run the end-to-end test. In the following example, we test the [sig-cli] tests of a 1.11 cluster:

$ kubetest --extract=release/stable-1.11 --up --test --down --test_args="--kubectl-path=$(pwd)/kubectl --ginkgo.focus=\[sig\-cli\]"

Run

Assuming the dispatcher has been compiled into this current directory, download the versioned kubectl binary here. NOTE: This download is assuming the major/minor version of the configured Kubernetes cluster is 1.10. If not, modify the downloaded release.

$ wget https://storage.googleapis.com/kubernetes-release/release/v1.10.11/bin/linux/amd64/kubectl
$ mv kubectl clibin/kubectl.1.10
$ chmod +x clibin/kubectl.1.10

Run the kubectl dispatcher. The verbosity is useful for debugging.

$ ./kubectl -v=5 --alsologtostderr version