kubectl plugin/wrapper to match kubectl binary version to current cluster version

kubectl-v

#!/bin/bash

set -e
cache=${XDG_CACHE_HOME:-$HOME/.cache}/kubectl-v
errors="$cache/errors-$$"
mkdir -p "$cache"

[[ $1 = "v" ]] && shift         # Avoid recursive calls

get_sys() {
    uname | tr '[:upper:]' '[:lower:]'
}

get_cpu() {
    local -r machine_hardware_name=$(uname -m)

    case "$machine_hardware_name" in
        x86_64) echo amd64 ;;
        powerpc64le|ppc64le) echo ppc64le ;;
        aarch64) echo arm64 ;;
        armv7l) echo arm ;;
        *) echo "$machine_hardware_name" ;;
    esac
}

fetch_kubectl() {
    [[ -x $2 ]] && return
    echo "Download kubectl $1"
    local sys cpu
    sys=$(get_sys)
    cpu=$(get_cpu)

    # ARM binaries not available before 1.20.0
    if [[ $sys = "darwin" && $cpu = "arm64" && $(semver compare $1 v1.20.0) = -1 ]]; then
        cpu="amd64"
    fi
    curl -L "https://storage.googleapis.com/kubernetes-release/release/$1/bin/${sys}/${cpu}/kubectl" -o "$2"
    chmod +x "$2"
}

link_kubectl() {
    ln -sf "$(basename "$1")" "$cache/$(basename "$2")"
}

fetch_kubectl_latest() {
    kubectl_latest="$cache/kubectl-latest"
    [[ -x $kubectl_latest ]] && return
    local -r stable_version=$(curl -s https://storage.googleapis.com/kubernetes-release/release/stable.txt)
    local -r kubectl_stable="$cache/kubectl-${stable_version}"
    fetch_kubectl "$stable_version" "$kubectl_stable"
    link_kubectl "$kubectl_stable" "$kubectl_latest"
}

current_cluster_name() {
    kubectl_cluster="$cache/kubectl-$($kubectl_default config view --minify -o jsonpath='{.clusters[].name}')"
    echo ${cluster_name/*\//} # Remove path prefixes (i.e. from arn URIs)
}

kubectl_path_for_current_cluster() {
    cluster_name=$($kubectl_default config view --minify -o jsonpath='{.clusters[].name}')
    cluster_name=${cluster_name/*\//} # Remove path prefixes (i.e. from arn URIs)
    echo "$cache/kubectl-$cluster_name"
}

fetch_kubectl_current() {
    kubectl_path=$(kubectl_path_for_current_cluster)
    [[ -x $kubectl_path ]] && return
    local current_version
    current_version=$($kubectl_default version --output=yaml 2> >(grep -v "version difference" >&2))
    current_version=${current_version/*gitVersion: } # Remove preamble
    current_version=${current_version%%-*}           # Remove suffixes
    kubectl_current="$cache/kubectl-$current_version"
    fetch_kubectl "$current_version" "$kubectl_current"
    link_kubectl "$kubectl_current" "$kubectl_path"
}

kubectl_default=${HOMEBREW_PREFIX:-/opt/homebrew}/bin/kubectl
[[ -x $kubectl_default ]] || { fetch_kubectl_latest && kubectl_default=$kubectl_latest; }

if [[ $1 = "config" ]]; then
    $kubectl_default "$@"
else
    if [[ $1 = "update" ]]; then
        kubectl_path=$(kubectl_path_for_current_cluster)
        rm $kubectl_path
        echo "Updating kubectl for ${kubectl_path/*kubectl-/}..."
        fetch_kubectl_current
        $kubectl_path version
    else
        fetch_kubectl_current
        $kubectl_path "$@"
    fi
fi

Setup

Put content into a file in $PATH, and make executable

$ chmod +x kubectl-v

Usage

Use as a kubectl plugin by prefixing arguments with v. E.g.

$ kubectl v version

Or call kubectl-v in a kubectl wrapper script or alias

Gotchas

• The --context argument is ignored to determine the cluster version, only the current-context is considered
• Standard kubectl binaries before v1.13.0 are not compatible with macOS Montery. You need to use special builds with updated Golang-libs for these