kubectl-ssh

#!/usr/bin/env bash

set -e

ssh_node() {
  node=$1
  image=${KUBECTL_SSH_IMAGE:-busybox}
  shift
  if [ "$node" = "" ]; then
    node=$(kubectl get node -o name "$@" | sed 's/node\///' | tr '\n' ' ')
    node=${node::-1}

    if [[ "$node" =~ " " ]]; then
      echo "Node name must be specified. Choose one of: [$node]"
      exit 1
    else
      echo "Single-node cluster detected. Defaulting to node $node"
    fi
  fi

  if [ $# -eq 1 ]; then
    command="$1"
    shift
  fi

  ns=default
  pod=$(
    kubectl create -n "$ns" -o name "$@" -f - <<EOF
apiVersion: v1
kind: Pod
metadata:
  generateName: ssh-node-
  labels:
    plugin: ssh-node
spec:
  nodeName: $node
  containers:
  - name: ssh-node
    image: $image
    imagePullPolicy: IfNotPresent
    command: ["chroot", "/host"]
    tty: true
    stdin: true
    stdinOnce: true
    securityContext:
      privileged: true
    volumeMounts:
    - name: host
      mountPath: /host
  volumes:
  - name: host
    hostPath:
      path: /
  hostNetwork: true
  hostIPC: true
  hostPID: true
  restartPolicy: Never
  tolerations:
    - operator: "Exists"
EOF
  )

  deletePod() {
    kubectl delete -n "$ns" "$pod" "$@" --wait=false
  }
  trap deletePod EXIT

  echo "Created $pod"
  echo "Waiting for container to start..."
  kubectl wait -n "$ns" --for=condition=Ready --timeout 120s "$pod" "$@" >/dev/null

  if [ -z "$command" ]; then
    kubectl attach -n "$ns" -it "$pod" -c ssh-node "$@"
  else
    kubectl exec -n "$ns" -it "$pod" ssh-node -- "$command"
  fi
}

ssh_pod() {
  # TODO: improve this
  if [ "$1" == "" ]; then
    echo "Pod name must be specified."
    exit 1
  fi
  # Use sh as a default and switch to bash if it's available
  # shellcheck disable=SC2016
  kubectl exec -it "$@" -- /bin/dash -c 'exec "$( command -v /bin/bash || echo /bin/sh )"'
}

print_usage() {
  echo "Provider-agnostic way of opening a remote shell to a Kubernetes node."
  echo
  echo "Enables you to access a node even when it doesn't run an SSH server or"
  echo "when you don't have the required credentials. Also, the way you log in"
  echo "is always the same, regardless of what provides the Kubernetes cluster"
  echo "(e.g. Minikube, Kind, Docker Desktop, GKE, AKS, EKS, ...)"
  echo
  echo "You must have cluster-admin rights to use this plugin."
  echo
  echo "The primary focus of this plugin is to provide access to nodes, but it"
  echo "also provides a quick way of running a shell inside a pod."
  echo
  echo "Examples: "
  echo "  # Open a shell to node of a single-node cluster (e.g. Docker Desktop)"
  echo "  kubectl ssh node"
  echo
  echo "  # Open a shell to node of a multi-node cluster (e.g. GKE)"
  echo "  kubectl ssh node my-worker-node-1"
  echo
  echo "  # Execute the command ls on a node my-worker-node-1"
  echo "  kubectl ssh node my-worker-node-1 ls"
  echo
  echo "  # Open a shell to a pod"
  echo "  kubectl ssh pod my-pod"
  echo
  echo "Usage:"
  echo "  kubectl ssh node [nodeName [command]]"
  echo "  kubectl ssh pod [podName] [-n namespace] [-c container]"
  exit 0
}

if [ "$1" == "--help" ]; then
  print_usage
fi

if [[ "$1" == node/* ]]; then
  nodeName=${1:5}
  shift
  ssh_node "$nodeName" "$@"
elif [ "$1" == "node" ]; then
  shift
  case "$1" in
  -*) nodeName="";;
  "") ;;
  *) nodeName="$1"; shift ;;
  esac

  ssh_node "$nodeName" "$@"
elif [[ "$1" == pod/* ]]; then
  ssh_pod "$@"
elif [ "$1" == "pod" ]; then
  shift
  ssh_pod "$@"
else
  print_usage
fi