Switch Rancher clusters from your terminal, updating / merging your kube config

rancher-cluster-switch.sh

#! /usr/bin/env bash
# Connect to one of our clusters via Rancher's CLI.

set -e


_RANCHER_URL="${1:-$RANCHER_URL}"
_RANCHER_TOKEN="${2:-$RANCHER_TOKEN}"
DEFAULT_CLUSTER="${3:-development}


##
# Print an error message to stderr.
_error()
{
    if [ $# -ne 1 ]
    then
        printf "Expected 1 argument to \`_error\`, received %s.\\n" "$#" >&2
        exit 1
    fi

    local message
    message="$1"

    printf "\e[2m\e[1mERROR\e[0m\e[2m: %s\e[0m\\n" "$message" >&2
}


##
# Print a warning message to stderr.
_warning()
{
    if [ $# -ne 1 ]
    then
        _error "Expected 1 argument to \`_warning\`, received $#.\\n"
        return 1
    fi

    local message
    message="$1"

    printf "\e[2m\e[1mWARNING\e[0m\e[2m: %s\e[0m\\n" "$message" >&2
}


##
# Get a user's response on a question to set environment variables.
# Call like `X="$(response "Enter your name: " "Emma")"`
# To set a default value on `X` if the user just hits enter.
response()
{
    if [ $# -eq 0 ]
    then
        _error "Must submit at least 2 arguments to \`response\` function for IO."
        return 1
    elif [ $# -gt 2 ]
    then
        _warning "received >2 arguments at response function, ignoring extra arguments"
    fi

    question="$1"
    default="$2"

    read -r -p "$question" var
    if [ "$var" ]
    then
        printf "%s" "$var"
    else
        if [ "$default" ]
        then
            _warning "Defaulting to $default"
        else
            _warning "Attempted to default, but no value given, returning \"\""
        fi
        printf "%s" "$default"
    fi

    return 0
}


if command -v pass >/dev/null && [ -z "$_RANCHER_TOKEN" ]; then
    _RANCHER_TOKEN="$(pass show rancher-token)"
elif [ -z "$_RANCHER_TOKEN" ]; then
    _error "must set RANCHER_TOKEN environment variable or set up pass"
    exit 1
fi

# Ensure we have some binaries this script requires.
if ! command -v kubectl >/dev/null; then
    _error "must install the kubectl CLI: https://kubernetes.io/docs/tasks/tools/"
    exit 1
fi

if ! command -v rancher >/dev/null; then
    _error "must install the Rancher CLI: https://github.com/rancher/cli"
    exit 1
fi

if ! command -v mapfile >/dev/null; then
    _error "must upgrade bash (brew install bash)"
    exit 1
fi

if ! command -v column >/dev/null; then
    _error "must upgrade util-linux (apt install util-linux)"
    exit 1
fi

# Ensure the expected directory structure is present.
if [ ! -d "$HOME"/.kube ]; then
    _warning "setting up ~/.kube/config, directory doesn't exist"
    mkdir "$HOME"/.kube
    touch "$HOME"/.kube/config
elif [ -d "$HOME"/.kube ] && [ ! -f "$HOME"/.kube/config ]; then
    _warning "setting up ~/.kube/config, directory doesn't exist"
    touch "$HOME"/.kube/config
fi


##
# Switch rancher cluster contexts.
rancher_switch_cluster()
{
    local cluster="$1"

    printf "Info: Attempting to create ~/.kube/config for cluster \"%s\"\\n" "$cluster"

    if ! rancher clusters kf "$cluster" > config.new; then
        if [ -f config.new ]; then rm config.new; fi
        exit 1
    fi

    # Flatten new kubeconfig into existing config and clean up.
    cp "$HOME"/.kube/config "$HOME"/.kube/config.bak
    KUBECONFIG=config.new:"$HOME"/.kube/config.bak kubectl config view --flatten > "$HOME"/.kube/config && \
        rm "$HOME"/.kube/config.bak config.new && \
        printf "Info: Successfully switched context to cluster \"%s\"\\n" "$cluster"
}


##
# Provide an interface to connect to a particular Rancher cluster.
rancher_select_cluster()
{
    local cluster _cluster i n clusters selected_cluster

    mapfile -t clusters < <(rancher clusters ls --format "{{ .Cluster.Name }}")
    clusters+=("all")
    i=1
    n="${#clusters[@]}"

    while true; do
        printf "Select a cluster:\\n\\n"
        for cluster in "${clusters[@]}"; do
            printf "(%s) %s\\n" "$i" "$cluster"
            (( i += 1 ))
        done | column -t && printf "\\n"

        selected_cluster="$(response "Select a cluster (by name or index): " "${DEFAULT_CLUSTER}")"

        # Ensure this cluster is in the list (slow, linear search), either by index or name, and call a context switch.
        i=1
        for cluster in "${clusters[@]}"; do
            if [ "$selected_cluster" = "$cluster" ]; then
                if [ "$selected_cluster" != "all" ]; then
                    rancher_switch_cluster "$selected_cluster"
                else
                    # Loop over all clusters and merge their configs to a dev's local kubeconfig, defaulting to ${DEFAULT_CLUSTER}.
                    for _cluster in "${clusters[@]}"; do
                        if [ "$_cluster" != "all" ]; then
                            rancher_switch_cluster "$_cluster"
                        fi
                    done
                    kubectl config use-context "${DEFAULT_CLUSTER}"
                fi
                return 0
            elif [ "$selected_cluster" = "$i" ]; then
                if [ "${clusters[$(( i - 1 ))]}" != "all" ]; then
                    rancher_switch_cluster "${clusters[$(( i - 1 ))]}"
                else
                    for _cluster in "${clusters[@]}"; do
                        if [ "$_cluster" != "all" ]; then
                            rancher_switch_cluster "$_cluster"
                        fi
                    done
                    kubectl config use-context "${DEFAULT_CLUSTER}"
                fi
                return 0
            elif [ "$i" -eq "$n" ]; then
                _error "Cluster \"$selected_cluster\" does not exist, try again"
                i=1
                break
            fi
            (( i += 1 ))
        done
    done
}


##
# Log in to our Rancher server to connect to clusters.
rancher_login()
{
    local token="$1"
    local url="$2"

    echo 1 | rancher login -t "$token" "$url" >/dev/null
}


rancher_login "$_RANCHER_TOKEN" "$_RANCHER_URL"
rancher_select_cluster


unset -v _RANCHER_TOKEN _RANCHER_URL DEFAULT_CLUSTER
unset -f _error _warning response rancher_select_cluster rancher_login rancher_switch_cluster