#!/usr/bin/env bash

# force_single_node - Manually promote a single coordinator node from a degraded cluster
# Part of the Parallel Virtual Cluster (PVC) system
#
#    Copyright (C) 2018-2020 Joshua M. Boniface <joshua@boniface.me>
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <https://www.gnu.org/licenses/>.
#
###############################################################################

set -o errexit
set -o pipefail

usage() {
    echo -e "Manually promote a single coordinator node from a degraded cluster"
    echo -e ""
    echo -e "DANGER: This action will cause a permanent split-brain within the cluster"
    echo -e "        which will have to be corrected manually upon cluster restoration."
    echo -e ""
    echo -e "This script is primarily designed for small clusters in situations where 2"
    echo -e "of the 3 coordinators have become unreachable or shut down. It will promote"
    echo -e "the remaining lone_node to act as a standalone coordinator, allowing basic"
    echo -e "cluster functionality to continue in a heavily degraded state until the"
    echo -e "situation can be rectified. This should only be done in exceptional cases"
    echo -e "as a disaster recovery mechanism when the remaining nodes will remain down"
    echo -e "for a significant amount of time but some VMs are required to run. In general,"
    echo -e "use of this script is not advisable."
    echo -e ""
    echo -e "Usage:"
    echo -e "  $0 <target_cluster> <lone_node>"
    echo -e ""
    echo -e "Important information:"
    echo -e " * The lone_node must be a fully-qualified name that is directly reachable from"
    echo -e "   the local system via SSH."
    echo -e " * The local user must have valid SSH access to the lone_node in the cluster."
    echo -e " * The user on the cluster node must have 'sudo' access."
}

fail() {
    echo -e "$@"
    exit 1
}

# Arguments
if [[ -z ${1} || -z ${2} ]]; then
    usage
    exit 1
fi
target_cluster="${1}"
lone_node="${2}"
lone_node_shortname="${lone_node%%.*}"

# Attempt to connect to the node
ssh ${lone_node} which pvc &>/dev/null || fail "Could not SSH to the lone_node host"

echo "Verification complete."

echo -n "Allowing Ceph single-node operation... "
temp_monmap="$( ssh ${lone_node} mktemp )"
ssh ${lone_node} "sudo systemctl stop ceph-mon@${lone_node_shortname}" &>/dev/null
ssh ${lone_node} "ceph-mon -i ${lone_node_shortname} --extract-monmap ${temp_monmap}" &>/dev/null
ssh ${lone_node} "sudo cp ${tmp_monmap} /etc/ceph/monmap.orig" &>/dev/null
mon_list="$( ssh ${lone_node} strings ${temp_monmap} | sort | uniq )"
for mon in ${mon_list}; do
    if [[ ${mon} == ${lone_node_shortname} ]]; then
        continue
    fi
    ssh ${lone_node} "sudo monmaptool ${temp_monmap} --rm ${mon}" &>/dev/null
done
ssh ${lone_node} "sudo ceph-mon -i ${lone_node_shortname} --inject-monmap ${temp_monmap}" &>/dev/null
ssh ${lone_node} "sudo systemctl start ceph-mon@${lone_node_shortname}" &>/dev/null
sleep 5
ssh ${lone_node} "sudo ceph osd set noout" &>/dev/null
echo "done."
echo -e "Restoration steps:"
echo -e "  sudo systemctl stop ceph-mon@${lone_node_shortname}"
echo -e "  sudo ceph-mon -i ${lone_node_shortname} --inject-monmap /etc/ceph/monmap.orig"
echo -e "  sudo systemctl start ceph-mon@${lone_node_shortname}"
echo -e "  sudo ceph osd unset noout"

echo -n "Allowing Zookeeper single-node operation... "
temp_zoocfg="$( ssh ${lone_node} mktemp )"
ssh ${lone_node} "sudo systemctl stop zookeeper"
ssh ${lone_node} "sudo awk -v lone_node=${lone_node_shortname} '{
FS="=|:"
if ( $1 ~ /^server/ ){
    if ($2 == lone_node) {
        print $0
    } else {
        print "#" $0
    }
} else {
    print $0
}
}' /etc/zookeeper/conf/zoo.cfg > ${temp_zoocfg}"
ssh ${lone_node} "sudo mv /etc/zookeeper/conf/zoo.cfg /etc/zookeeper/conf/zoo.cfg.orig"
ssh ${lone_node} "sudo mv ${temp_zoocfg} /etc/zookeeper/conf/zoo.cfg"
ssh ${lone_node} "sudo systemctl start zookeeper"
echo "done."
echo -e "Restoration steps:"
echo -e "  sudo systemctl stop zookeeper"
echo -e "  sudo mv /etc/zookeeper/conf/zoo.cfg.orig /etc/zookeeper/conf/zoo.cfg"
echo -e "  sudo systemctl start zookeeper"
ssh ${lone_node} "sudo systemctl stop ceph-mon@${lone_node_shortname}"

echo ""
ssh ${lone_node} "sudo pvc status 2>/dev/null"