rsyncr

#!/bin/bash

# A cron job to synchronise filesystems between multiple nodes.
# Soft link this script under /etc/cron.{daily,hourly,weekly} as appropriate.

set -eo pipefail
shopt -s nullglob
err_report() {
    echo "errexit on line $(caller)" >&2
}
trap err_report ERR

CONFIG=/etc/rsyncr.conf
YQ=$(which yq || echo "/usr/local/bin/yq")

if [[ ! -f /etc/rsyncr.conf ]]; then
    echo "No configuration"
    exit 0
fi

# If another rsyncr job is running, complain and crash out.
if ps ax|grep '[l]ogger -t rsyncr' >/dev/null; then
    echo "An rsyncr process is already running; aborting!"
    exit 1
fi

# Only run if we are the designated master. This allows us to sync our own
# configuration.
master=$($YQ -r ".master" < $CONFIG)
[[ $master && "$master" == $(hostname --fqdn) ]] || exit 0

nodes=($($YQ -r ".nodes + .slaves|.[]" < $CONFIG))
includes=($($YQ -r ".includes|.[]" < $CONFIG))
excludes=($($YQ -r ".excludes|.[]?" < $CONFIG))
options=$($YQ -r ".options|.[]?" < $CONFIG)
sshkey=$($YQ -r ".sshkey" < $CONFIG)

include_list=()
for include in "${includes[@]}"; do
    case "$include" in
    "")
        # Strip empty strings, as rsync maps these to "/" (!!!)
        ;;
    *)
        include_list=("${include_list[@]}" "$include")
        ;;
    esac
done

if [[ ! ${include_list[0]:-} ]]; then
    echo "Must include at least one source"
    exit 2
fi

exclude_flags=()
for exclude in "${excludes[@]}"; do
    exclude_flags=("${exclude_flags[@]}" "--exclude" "$exclude")
done

option_flags=()
for option in "${options[@]}"; do
    case "$option" in
    "delete")
        option_flags=("${exclude_flags[@]}" "--$option")
        ;;
    "")
        # If yq finds no options, it returns the empty string; ignore this
        ;;
    *)
        echo "Unsupported option '$option'; aborting"
        exit 99
        ;;
    esac
done

# Also sync our own configuration, including ssh keys
include_list=("${include_list[@]}" "$CONFIG" "$sshkey" "$sshkey.pub")

# fire in the hole

cd /
for node in "${nodes[@]}"; do
    [[ $node && $node != $master ]] || continue
    rsync -a --relative -e "ssh -i $sshkey" "${option_flags[@]}" \
        "${exclude_flags[@]}" "${include_list[@]}" \
        ${node}:/ 2>&1 | logger -t rsyncr
done