Set mysql server_id based on instance-id

Do nothing if we are booted on a server which has no instance-id set,
such as a non-cloud VM or server.

Change-Id: I6df81edbea1b2b4e4f1ef11a9f2ddaf100d98eda

elements/mysql/install.d/10-mysql

@@ -6,5 +6,6 @@ set -e
 set -o xtrace
 
 install -D -m 0644 -o root -g root  $(dirname $0)/my.cnf /etc/mysql/my.cnf
+install $(dirname $0)/mysql-set-server-id.upstart /etc/init/mysql-set-server-id.conf
 
 install-packages sysstat mytop percona-toolkit mysql-server-5.5 mysql-client-5.5

elements/mysql/install.d/mysql-set-server-id.upstart

@@ -0,0 +1,27 @@
+# vim: syntax=upstart
+description "Set mysql server_id based on instance-id"
+
+start on starting mysql
+task
+
+env INSTANCE_ID="/var/lib/cloud/data/instance-id"
+env CONF_TARGET="/etc/mysql/conf.d/server_id.cnf"
+
+pre-start script
+    if ! [ -e $INSTANCE_ID ] ; then
+        stop
+        exit 0
+    fi
+end script
+
+script
+    instance=$(cat $INSTANCE_ID)
+    server_id=$(python -c "print 0x${instance##i-}")
+    cat > $CONF_TARGET.new <<EOF
+# Generated by mysql-set-server-id upstart job $(date)
+# From $INSTANCE_ID ${instance}
+[mysqld]
+server_id = $server_id
+EOF
+    mv -f $CONF_TARGET.new $CONF_TARGET
+end script