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Notification Script Example¶
Nodes can call a notification script when changes happen in the membership of the cluster, that is when nodes join or leave the cluster. You can specify the name of the script the node calls using the wsrep_notify_cmd. While you can use whatever script meets the particular needs of a deployment, you may find it helpful to consider the example below as a starting point.
#!/bin/sh -eu
# This is a simple example of wsrep notification script (wsrep_notify_cmd).
# It will create 'wsrep' schema and two tables in it: 'membership' and 'status'
# and insert data into them on every membership or node status change.
#
# Edit parameters below to specify the address and login to server.
USER=root
PSWD=rootpass
HOST=<host_IP_address>
PORT=3306
SCHEMA="wsrep"
MEMB_TABLE="$SCHEMA.membership"
STATUS_TABLE="$SCHEMA.status"
BEGIN="
SET wsrep_on=0;
DROP SCHEMA IF EXISTS $SCHEMA; CREATE SCHEMA $SCHEMA;
CREATE TABLE $MEMB_TABLE (
idx INT UNIQUE PRIMARY KEY,
uuid CHAR(40) UNIQUE, /* node UUID */
name VARCHAR(32), /* node name */
addr VARCHAR(256) /* node address */
) ENGINE=MEMORY;
CREATE TABLE $STATUS_TABLE (
size INT, /* component size */
idx INT, /* this node index */
status CHAR(16), /* this node status */
uuid CHAR(40), /* cluster UUID */
prim BOOLEAN /* if component is primary */
) ENGINE=MEMORY;
BEGIN;
DELETE FROM $MEMB_TABLE;
DELETE FROM $STATUS_TABLE;
"
END="COMMIT;"
configuration_change()
{
echo "$BEGIN;"
local idx=0
for NODE in $(echo $MEMBERS | sed s/,/\ /g)
do
echo "INSERT INTO $MEMB_TABLE VALUES ( $idx, "
# Don't forget to properly quote string values
echo "'$NODE'" | sed s/\\//\',\'/g
echo ");"
idx=$(( $idx + 1 ))
done
echo "
INSERT INTO $STATUS_TABLE
VALUES($idx, $INDEX,'$STATUS', '$CLUSTER_UUID', $PRIMARY);
"
echo "$END"
}
status_update()
{
echo "
SET wsrep_on=0;
BEGIN;
UPDATE $STATUS_TABLE SET status='$STATUS';
COMMIT;
"
}
COM=status_update # not a configuration change by default
while [ $# -gt 0 ]
do
case $1 in
--status)
STATUS=$2
shift
;;
--uuid)
CLUSTER_UUID=$2
shift
;;
--primary)
[ "$2" = "yes" ] && PRIMARY="1" || PRIMARY="0"
COM=configuration_change
shift
;;
--index)
INDEX=$2
shift
;;
--members)
MEMBERS=$2
shift
;;
esac
shift
done
# Undefined means node is shutting down
if [ "$STATUS" != "Undefined" ]
then
$COM | mysql -B -u$USER -p$PSWD -h$HOST -P$PORT
fi
exit 0
Path and Permissions
After you modify this script to fit your requirements, you need to move it into a directory in the $PATH or the binaries directory for your system. On Linux, the binaries directory is typically at /usr/bin, while on FreeBSD it is at /usr/local/bin.
# mv my-wsrep-notify.sh /usr/bin
In addition to this, given that the notification command contains your root password, change the ownership to the mysql user and make sure the script is executable only by that user.
# chown mysql:mysql /usr/bin/my-wsrep-notify.sh
# chmod 700 /usr/bin/my-wsrep-notify.sh.
This ensures that only the mysql user can execute and read the notification script, preventing all other users from seeing the root password.
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