This Bash script automates setting up a MySQL replica running in Docker by connecting to a Dockerized master (potentially remote via SSH), creating a replication user, performing a consistent backup with binlog coordinates, transferring the backup, generating and launching a `docker-compose` stack on the replica host, importing the data, configu…

replica_bootstrap.sh

#!/usr/bin/env bash
#
# replica_bootstrap.sh – quick (re)bootstrap of a MySQL replica in Docker
# Author: [email protected]
# ----------------------------------------------------------------------

set -euo pipefail
IFS=$'\n\t'

##############################################################################
# CONFIGURATION – change what you need and/or export as env‑vars beforehand
##############################################################################
MASTER_CTN="mysql"
MASTER_ROOT_PW="password"

SLAVE_HOST="10.0.0.1"
SLAVE_SSH="root@$SLAVE_HOST"
SLAVE_STACK_DIR="/opt/mysql-replica"
SLAVE_CTN="replica-db"
SLAVE_EXPORTER_CTN="mysqld-exporter"

REPL_USER="replicator"
REPL_PW="$(openssl rand -base64 24)"     # $(openssl rand -base64 24) auto‑generate unless REPL_PW is preset

DUMP_FILE="/tmp/mysql_replica_$(date +%Y%m%d_%H%M%S).sql.gz"

##############################################################################
# HELPER FUNCTIONS
##############################################################################
banner() { printf '\n\033[1;36m▶ %s\033[0m\n' "$*"; }

die() { printf '\033[1;31m✖ %s\033[0m\n' "$*" >&2; exit 1; }

mysql_exec() {
  docker exec -i "$MASTER_CTN" mysql -uroot -p"$MASTER_ROOT_PW" "$@" 2>/dev/null
}

health_check() {
  banner "Health‑checking $1 ..."
  if [[ $1 == "master" ]]; then
      docker exec -e MYSQL_PWD="$MASTER_ROOT_PW" "$MASTER_CTN" \
                 mysqladmin ping -uroot >/dev/null \
      || die "Master MySQL is not responding"
  else
    ssh "$SLAVE_SSH" "docker ps --format '{{.Names}}' | grep -q '^$SLAVE_CTN$'" \
      && ssh "$SLAVE_SSH" "docker exec $SLAVE_CTN mysqladmin ping -uroot -p'$MASTER_ROOT_PW' >/dev/null" \
      || echo "(slave not up yet – will come up later)"
  fi
  printf '✔ OK\n'
}

##############################################################################
# 1. HEALTH CHECK
##############################################################################
health_check master

##############################################################################
# 2. CREATE/RESET REPLICATION USER
##############################################################################
banner "Creating replication user on master (if absent) ..."
mysql_exec -e "CREATE USER IF NOT EXISTS '$REPL_USER'@'%' IDENTIFIED WITH mysql_native_password BY '$REPL_PW';
               GRANT REPLICATION SLAVE, REPLICATION CLIENT ON *.* TO '$REPL_USER'@'%';
               FLUSH PRIVILEGES;"

##############################################################################
# 3. CONSISTENT BACKUP WITH LIGHT LOCK
##############################################################################
banner "Dumping master (with --single-transaction, quick) ..."
# We still FLUSH TABLES WITH READ LOCK very briefly to freeze binlog position
mysql_exec -e "FLUSH TABLES WITH READ LOCK;"
LOCK_ACTIVE=1
trap '[[ ${LOCK_ACTIVE:-0} == 1 ]] && mysql_exec -e "UNLOCK TABLES;"' EXIT

# Grab current coordinates
CURRENT_STATUS=$(mysql_exec -e "SHOW MASTER STATUS\G")
BINLOG_FILE=$(printf '%s\n' "$CURRENT_STATUS" | awk '/File:/ {print $2}')
BINLOG_POS=$(printf '%s\n'  "$CURRENT_STATUS" | awk '/Position:/ {print $2}')

docker exec -e MYSQL_PWD="$MASTER_ROOT_PW" "$MASTER_CTN" mysqldump \
  -uroot --single-transaction --quick --source-data=2 \
  --set-gtid-purged=OFF --all-databases --triggers --routines --events \
  | gzip > "$DUMP_FILE"

mysql_exec -e "UNLOCK TABLES;"
LOCK_ACTIVE=0
trap - EXIT

##############################################################################
# 4. COPY DUMP AND BUILD SLAVE STACK
##############################################################################
banner "Copying dump to slave ..."
scp "$DUMP_FILE" "$SLAVE_SSH:/tmp/" >/dev/null

banner "Generating docker‑compose on slave ..."
cat <<EOF | ssh "$SLAVE_SSH" "mkdir -p $SLAVE_STACK_DIR && cat > $SLAVE_STACK_DIR/docker-compose.yml"
version: "3.9"
services:
  $SLAVE_CTN:
    image: mysql:8.1
    container_name: $SLAVE_CTN
    environment:
      MYSQL_ROOT_PASSWORD: "$MASTER_ROOT_PW"
      MYSQL_DATABASE: fanus
    command:
      - --server-id=2
      - --log-bin=mysqld-bin
      - --binlog_format=ROW
      - --relay_log=mysqld-relay-bin
      - --read_only=1
    volumes:
      - db-data:/var/lib/mysql
    restart: unless-stopped
    ports:
      - "$SLAVE_HOST:3306:3306"

  $SLAVE_EXPORTER_CTN:
    image: prom/mysqld-exporter:latest
    container_name: $SLAVE_EXPORTER_CTN
    environment:
      MYSQLD_EXPORTER_PASSWORD: "$MASTER_ROOT_PW"
    command:
      - "--mysqld.username=root"
      - "--mysqld.address=127.0.0.1:3306"
    depends_on: [$SLAVE_CTN]
    restart: unless-stopped
    ports:
      - "9104:9104"

volumes:
  db-data:
EOF

banner "Starting slave stack ..."
ssh "$SLAVE_SSH" "cd $SLAVE_STACK_DIR && docker compose up -d --wait"

banner "Waiting for MySQL inside slave to accept connections ..."
ssh "$SLAVE_SSH" '
  until docker exec '"$SLAVE_CTN"' \
         mysqladmin -h127.0.0.1 -uroot -p"'"$MASTER_ROOT_PW"'" ping --silent
  do
    sleep 2
  done
'

##############################################################################
# 5. IMPORT DUMP AND CONFIGURE REPLICA
##############################################################################
banner "Importing dump into slave (this might take a few minutes) ..."
ssh "$SLAVE_SSH" "
  gunzip -c /tmp/$(basename "$DUMP_FILE") |
  docker exec -i $SLAVE_CTN \
    mysql -h127.0.0.1 -uroot -p'$MASTER_ROOT_PW'
"


banner "Setting up CHANGE MASTER TO ..."
MASTER_IP=$(hostname -I | awk '{print $2}')   # crude but works in single‑IP env
MASTER_PORT=12121
ssh "$SLAVE_SSH" "docker exec $SLAVE_CTN mysql -uroot -p'$MASTER_ROOT_PW' -e \"
  STOP SLAVE;
  RESET SLAVE ALL;
  CHANGE MASTER TO
    MASTER_HOST='$MASTER_IP',
    MASTER_PORT='$MASTER_PORT',
    MASTER_USER='$REPL_USER',
    MASTER_PASSWORD='$REPL_PW',
    MASTER_LOG_FILE='$BINLOG_FILE',
    MASTER_LOG_POS=$BINLOG_POS,
    GET_MASTER_PUBLIC_KEY=1;
  START SLAVE;
\""

##############################################################################
# 6. VERIFY REPLICATION
##############################################################################
banner "Waiting for slave to catch up ..."
for i in {1..30}; do
  SECS_BEHIND=$(ssh "$SLAVE_SSH" "docker exec $SLAVE_CTN mysql -N -uroot -p'$MASTER_ROOT_PW' -e 'SHOW SLAVE STATUS\G' | awk '/Seconds_Behind_Master:/ {print \$2+0}'")
  if [[ $SECS_BEHIND -eq 0 ]]; then
    printf '\033[1;32m✓ Replication healthy. Done.\033[0m\n'
    exit 0
  fi
  sleep 2
done

die "Replication did not converge in time; check the slave's log."