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How To: Configure HA Fencing Settings

How To: Configure HA Fencing Settings

Release Classification Level DB Platform Categories
3.11+ How To
ALL Configuration

 

QUESTION
  1. Why do I need to configure HA fencing ?
  2. Which HA fencing options can I choose from ?
ANSWER

 

1. Starting from ScaleArc version 3.11 GA, ScaleArc improves High Availability with option for fencing. This feature significantly improves HA stability by introducing third member of the HA, called 'witness'.

In case of having ScaleArc HA pair, it is mandatory to configure Fence Settings either immediatelly after the upgrade from ScaleArc vesions below 3.11 GA or after the new ScaleArc installation at 3.11 GA.

This article describes three possible ways of how to configure HA fencing from the configuration page in the GUI.

2. Before the user starts configuring fencing, it has to be decided, which one of the three options will best suit organization's needs:

1. ScaleArc Cluster

2. External DB Server

3. SSH Server

 

Option 1: ScaleArc Cluster (Recommended)

Any of the clusters, defined under the CLUSTERS tab in the GUI, can be used as a witness member.

Note: This configuration is recommended over the other two options.

Go to the SETTINGS --> HA Settings --> in Fence Settings select 'ScaleArc Cluster (Recommended)' option and select the cluster name of your choice from the drop-down menu.

 

 

If configured with this option, each of the ScaleArcs from the HA pair will create a tiny logical database on the main Read+Write DB server of that cluster. These databases contain very simple tables with the status information, for example about which is the primary and secondary ScaleArc from the HA pair, continuously updated timestamp, etc. See the example for SQL Server in the below screenshot, similar applies to other DB types:

 

User credentials used to create such logical databases are the same as for the initial cluster creation in ScaleArc, selected from the drop-down menu. For example if user 'sa' was used to create this cluster of SQL Server type in ScaleArc, the same user will be used to create fencing logical DB and its tables.

 

Option 2: External DB Server

The user can use an external DB server to participate in the HA as a witness member. 

Go to the SETTINGS --> HA Settings --> in Fence Settings select 'External DB Server' option.

Enter 'DB Server' IP or hostname, Port, Username and Password for the DB user to create fencing logical DB.

 

Each of the HA pair member will create logical DB with fencing information inside, just like in the Option 1 above.

 

Option 3: SSH Server

An external SSH sever can be used as a witness too. It can be any VM or baremetal machine running ssh daemon, with specified port accessible through the network from each of the ScaleArcs in HA pair.

Note: Do not use any of the ScaleArcs from the HA pair, you're configuring fencing for, as a witness.

Go to the SETTINGS --> HA Settings --> in Fence Settings select 'SSH Server'

Enter 'SSH Server' IP, port, Username and Password, or enter SSH Key in the 'Provide SSH Key' option.

 

 

Each of the ScaleArcs from the HA pair will create set of folders and ASCII files, holding HA status information on this remote SSH server, see the example: 

 



If you are experiencing issues with ScaleArc or with any of it's features, please contact ScaleArc Support. We are available 24x7 by phone at 855 800 7225 or +1 408 412 7315. For general support inquiries, you can also e-mail us at support@scalearc.com.

 

Permalink: https://support.scalearc.com/kb/articles/4249