Backup all indexes in Elastic Search (ES) in an archive

backup-data.sh

#!/bin/bash
# See https://gist.github.com/593100533a7dbb4474612f9adb8f8ff6 for more info

# This script backup data from a ES instance to disk and create a xz archive with the command to restore it
# You need to have jq ( https://stedolan.github.io/jq/ ) and elasticdump ( https://www.npmjs.com/package/elasticdump ) installed


# source ES instance
DEFAULT_ESR='http://locahost:9200' # Edit this
ESR=${1:-$DEFAULT_ESR} # Or just use $1 to add the Elastic Search url

# Tune this reg expression to filter the indexes you want to backup
DEFAULT_REGEX='.*'
REGEX=${2:-$DEFAULT_REGEX}

DEFAULT_CMD='elasticdump' # You can use your own clone of elasticdump. Ex: '/Users/youruser/my-projects/elasticsearch-dump/bin/elasticdump'
CMD=${3:-$DEFAULT_CMD}

######################
# Backup!
######################

BACKUP_FOLDER_BASE=$(mktemp -d 2>/dev/null || mktemp -d -t 'es-backup')
BACKUP_FOLDER="${BACKUP_FOLDER_BASE}/backup"
RESTORE_FILE="$BACKUP_FOLDER/restore.sh"

mkdir -p $BACKUP_FOLDER
echo "# $0 [<elastic_search_url>]" >> $RESTORE_FILE
echo "# If <elastic_search_url> is not specified, it will use '${ESR}'" >> $RESTORE_FILE
echo "# elasticdump ( https://www.npmjs.com/package/elasticdump ) needs to be installed." >> $RESTORE_FILE
echo "# See https://gist.github.com/593100533a7dbb4474612f9adb8f8ff6 for more info" >> $RESTORE_FILE

echo "" >> $RESTORE_FILE
echo "# set -x # Uncomment this to debug" >> $RESTORE_FILE
echo "ES_DEFAULT_INSTANCE='${ESR}';" >> $RESTORE_FILE
echo "ES_INSTANCE=\"\${1:-\$ES_DEFAULT_INSTANCE}\";" >> $RESTORE_FILE
echo "" >> $RESTORE_FILE
chmod 755 $RESTORE_FILE


######################
# Backup indexes
######################

duplicate_index() {
    local in=$1
    local out=$2
    local index=$3
    shift
    shift
    shift
    for i; do
      local folder="$out/${index}";
      local full_in="${in}/${index}";
      local full_out="${folder}/${i}";
      mkdir -p $folder
      echo " ----> Backing up '${in}/${index}' ('$i')"
      $CMD \
        --limit=9999 \
        --input=${full_in} \
        --output=${full_out} \
        --type=$i
        if [ $? -eq 0 ]; then
            echo "$CMD --input=\"./${index}/${i}\" --output=\"\$ES_INSTANCE/${index}\" --type=$i;" >> $RESTORE_FILE
        else
            echo " !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
            echo " !!! Failed to backup '${index}' ('$i')"
            echo " !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"
        fi
    done
}

indexes=$(curl $ESR/_aliases?pretty=1 | jq --raw-output 'keys | .[]')

echo "$indexes" | while read -r current_index; do
  if [[ $current_index =~ $REGEX ]]
  then
    echo " --> Coping '$current_index'";
    duplicate_index "$ESR" "$BACKUP_FOLDER" "$current_index" analyzer settings mapping alias data
  else
    echo " !!--> Skipping '$current_index' that does not match the REGEX '$REGEX'";
  fi
done;

echo "" >> $RESTORE_FILE

############
# Archive
############

TODAY=$(date +%Y-%m-%d-%H-%M)
CURRENT_FOLDER=$(pwd)
ARCHIVE_NAME="es-backup-${TODAY}.tar.xz"
echo "Done dumping from ES. Creating a compressed file '$ARCHIVE_NAME'."
cd "$BACKUP_FOLDER_BASE"
XZ_OPT=-9 tar cJf "${CURRENT_FOLDER}/$ARCHIVE_NAME" .
cd "$CURRENT_FOLDER"
echo "Done archiving. You can decompress it with 'tar PxJf $ARCHIVE_NAME' and use 'restore.sh [<elastic_search_url>]' to restore it"
rm -rf "$BACKUP_FOLDER"

Can you explain this code ........