Chapter 3. Locate an Idle Node

Procedure

1. Retrieve the virtual IP address HAProxy is listening on to identify which node is active.

   [root@overcloud-controller-0]# grep -A1 mysql /etc/haproxy/haproxy.cfg

   Copy to Clipboard Toggle word wrap

   The result will look similar to this:

   listen mysql
     bind 192.0.2.18:3306

   Copy to Clipboard Toggle word wrap

2. Retrieve the username and password of a user allowed to connect to the virtual IP address. For example, the nova user and password from /etc/nova/nova.conf typically has these credentials.

   [root@overcloud-controller-0 heat-admin]# crudini --get /etc/nova/nova.conf database connection

   Copy to Clipboard Toggle word wrap

   Or

   [root@overcloud-controller-0 heat-admin]# grep mysql /etc/nova/nova.conf

   Copy to Clipboard Toggle word wrap

   The result should look something like this:

   connection=mysql+pymysql://nova:xvsZqeaJn2fYwMK8NbscAJ6xG@172.16.2.5/nova

   Copy to Clipboard Toggle word wrap

   The username and password in the foregoing example are nova and xvsZqeaJn2fYwMK8NbscAJ6xG respectively. The next step requires the username and password retrieved in this step.

3. Connect to the database over the virtual IP address to get the name of the targeted node.

   [root@overcloud-controller-0]# mysql -u <username> -p -h 192.0.2.18 -nNE -e "show variables like 'hostname';"
   Enter password: ****

   Copy to Clipboard Toggle word wrap

   Replace <username> with a user allowed to connect to the virtual IP address. The command line interface will prompt for a password. The result should look similar to this:

   ************************ 1. row ************************
   hostname
   overcloud-controller-0.example.com

   Copy to Clipboard Toggle word wrap

   In the foregoing example, overcloud-controller-0 is the active node targeted by HAProxy.

4. Ensure the remaining hot standby nodes are connected and in sync. In the following example, assume overcloud-controller-1 and overcloud-controller-2 are the hot standby nodes.

   [root@overcloud-controller-0]# curl overcloud-controller-1.example.com:9200 overcloud-controller-2.example.com:9200

   Copy to Clipboard Toggle word wrap

   If the remaining nodes are connected and in sync with the active node targeted by HAProxy, the result should look similar to this:

   Galera cluster node is synced.
   Galera cluster node is synced.

   Copy to Clipboard Toggle word wrap
   Important

   Execute the backup procedure on a hot standby node that is connected to the cluster and synchronized with the active node that HAProxy is targeting.