Add way to backup from MariaDB replica server

ProxySQL reports its version to MySQL clients,
causing the backup process to fail when ProxySQL is used.

This patch adds a new script that handles backups from
the replica server directly, without modifying the original
backup script. The new script retrieves the server address
via the load balancer and connects directly to the replica
server to execute the backup.

Moreover, this reduces the risk that the backup will be inconsistent
or that it will block OpenStack MySQL clients, because they are
connected to a different server, and no one is connected to the replica,
or that it will overload the load balancer (such as ProxySQL or HAProxy)
which listens on the VIP.

Closes-Bug: #2080818
Change-Id: Ibf7e40e8b059d733e114963022df06180249c650

2 files changed, 139 insertions, 1 deletions

diff --git a/docker/mariadb/mariadb-server/Dockerfile.j2 b/docker/mariadb/mariadb-server/Dockerfile.j2
index 2be384f6d..b0f49ac09 100644
--- a/docker/mariadb/mariadb-server/Dockerfile.j2
+++ b/docker/mariadb/mariadb-server/Dockerfile.j2
@@ -39,9 +39,12 @@ COPY mariadb_sudoers /etc/sudoers.d/kolla_mariadb_sudoers
 COPY extend_start.sh /usr/local/bin/kolla_extend_start
 COPY security_reset.expect /usr/local/bin/kolla_security_reset
 COPY backup.sh /usr/local/bin/kolla_mariadb_backup.sh
+COPY backup_replica.sh /usr/local/bin/kolla_mariadb_backup_replica.sh
 
 RUN chmod 644 /usr/local/bin/kolla_extend_start \
-    && chmod 755 /usr/local/bin/kolla_security_reset /usr/local/bin/kolla_mariadb_backup.sh \
+    && chmod 755 /usr/local/bin/kolla_security_reset \
+                 /usr/local/bin/kolla_mariadb_backup.sh \
+                 /usr/local/bin/kolla_mariadb_backup_replica.sh \
     && chmod 750 /etc/sudoers.d \
     && chmod 440 /etc/sudoers.d/kolla_mariadb_sudoers \
     && rm -rf /var/lib/mysql/*
diff --git a/docker/mariadb/mariadb-server/backup_replica.sh b/docker/mariadb/mariadb-server/backup_replica.sh
new file mode 100644
index 000000000..7f86a18a7
--- /dev/null
+++ b/docker/mariadb/mariadb-server/backup_replica.sh
@@ -0,0 +1,135 @@
+#!/usr/bin/env bash
+
+set -eu
+set -o pipefail
+
+BACKUP_DIR=/backup/
+DEFAULT_MY_CNF="/etc/mysql/my.cnf"
+REPLICA_MY_CNF="$(mktemp)"
+RETRY_INTERVAL=5  # Interval between retries (in seconds)
+MAX_RETRIES=12    # Max retries (12 retries * 5 seconds = 60 seconds)
+
+# Cleanup function to remove the REPLICA_MY_CNF file
+cleanup() {
+    rm -f "${REPLICA_MY_CNF}"
+}
+
+# Set trap to ensure cleanup occurs on exit or error
+trap cleanup EXIT
+
+cd "${BACKUP_DIR}"
+
+# Execute a full backup
+backup_full() {
+    echo "Taking a full backup"
+    LAST_FULL_DATE=$(date +%d-%m-%Y-%s)
+    mariabackup \
+        --defaults-file="${REPLICA_MY_CNF}" \
+        --backup \
+        --stream=mbstream \
+        --history="${LAST_FULL_DATE}" | gzip > \
+        "${BACKUP_DIR}/mysqlbackup-${LAST_FULL_DATE}.qp.mbc.mbs.gz" && \
+    echo "${LAST_FULL_DATE}" > "${BACKUP_DIR}/last_full_date"
+}
+
+# Execute an incremental backup
+backup_incremental() {
+    if [ -r "${BACKUP_DIR}/last_full_date" ]; then
+        LAST_FULL_DATE=$(cat "${BACKUP_DIR}/last_full_date")
+    else
+        LAST_FULL_DATE=""
+    fi
+    if [ ! -z "${LAST_FULL_DATE}" ]; then
+        echo "Taking an incremental backup"
+        mariabackup \
+            --defaults-file="${REPLICA_MY_CNF}" \
+            --backup \
+            --stream=mbstream \
+            --incremental-history-name="${LAST_FULL_DATE}" \
+            --history="${LAST_FULL_DATE}" | gzip > \
+            "${BACKUP_DIR}/incremental-$(date +%H)-mysqlbackup-${LAST_FULL_DATE}.qp.mbc.mbs.gz"
+    else
+        echo "Error: Full backup don't exist."
+        exit 1
+    fi
+}
+
+# Retry logic for database queries
+retry_mysql_query() {
+    local query="$1"
+    local result=""
+    local attempt=1
+
+    while [ ${attempt} -le ${MAX_RETRIES} ]; do
+        result=$(mysql -h "${HOST}" -u "${USER}" -p"${PASS}" -s -N -e "${query}" 2>/dev/null || true)
+        if [ -n "${result}" ]; then
+            echo "${result}"
+            return 0
+        fi
+        echo "Attempt ${attempt}/${MAX_RETRIES} failed. Retrying in ${RETRY_INTERVAL} seconds..."
+        sleep "${RETRY_INTERVAL}"
+        attempt=$((attempt + 1))
+    done
+
+    echo "Error: Failed to execute the query after ${MAX_RETRIES} attempts."
+    return 1
+}
+
+get_and_set_replica_server() {
+    HOST="$(grep '^host' "${DEFAULT_MY_CNF}" | awk -F '=' '{print $2}' | xargs)"
+    USER="$(grep '^user' "${DEFAULT_MY_CNF}" | awk -F '=' '{print $2}' | xargs)"
+    PASS="$(grep '^password' "${DEFAULT_MY_CNF}" | awk -F '=' '{print $2}' | xargs)"
+
+    ALL_HOSTS_SELECT="SELECT REGEXP_REPLACE(VARIABLE_VALUE, ':[0-9]*','') FROM information_schema.GLOBAL_STATUS WHERE VARIABLE_NAME = 'wsrep_incoming_addresses';"
+    ALL_HOSTS=$(retry_mysql_query "${ALL_HOSTS_SELECT}")
+    if [ -z "${ALL_HOSTS}" ]; then
+        echo "Backup failed due to inability to fetch a list of servers."
+        exit 1
+    fi
+
+    ACTIVE_HOST_SELECT='SELECT @@hostname;'
+    ACTIVE_HOST=$(retry_mysql_query "${ACTIVE_HOST_SELECT}" | xargs getent hosts | awk '{print $1}')
+    if [ -z "${ACTIVE_HOST}" ]; then
+        echo "Backup failed due to inability to fetch active host."
+        exit 1
+    fi
+
+    # Multinode
+    if echo "${ALL_HOSTS}" | grep -q ','; then
+        for server in $(echo "${ALL_HOSTS}" | tr ',' '\n'); do
+            if [[ "${server}" != "${ACTIVE_HOST}" ]]; then
+                REPLICA_HOST="${server}"
+                break
+            fi
+        done
+    # Single node
+    else
+        REPLICA_HOST="${ALL_HOSTS}"
+    fi
+    if [ -z "${REPLICA_HOST}" ]; then
+        echo "Backup failed due to inability to determine replica host."
+        exit 1
+    fi
+
+    cp "${DEFAULT_MY_CNF}" "${REPLICA_MY_CNF}"
+    sed -i "s/${HOST}/${REPLICA_HOST}/g" "${REPLICA_MY_CNF}"
+}
+
+if [ -n "${BACKUP_TYPE}" ]; then
+    get_and_set_replica_server
+    case "${BACKUP_TYPE}" in
+        "full")
+        backup_full
+        ;;
+        "incremental")
+        backup_incremental
+        ;;
+        *)
+        echo "Only full or incremental options are supported."
+        exit 1
+        ;;
+    esac
+else
+    echo "You need to specify either full or incremental backup options."
+    exit 1
+fi