This chapter describes how to enable high availability by configuring Image Modified for automatic failover of pico instances.

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For batch processing, a shared or clustered storage should be used. For stateful real-time scenarios with session management, session information should be persisted, using a distributed storage such as CouchBase.

When Image Modified is installed in an Open Stack cloud you can use Corosync and Pacemaker for monitoring. In Amazon Web Services you can use CloudWatch to perform the monitoring and Auto Scale to dynamically recreate a failed node. 

Overview

Image Modified provides HA monitor scripts that are executed by the cluster management software. After interpreting the result, additional scripts are available to start and stop pico instances. The provided scripts typically requires some amount of modification in order to work with your CMS product.

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Configuring the cluster monitoring software is beyond the scope of the documentation. See the applicable third party documentation for this purpose. It is important to configure dependencies and availability of the resources within the cluster correctly. The cluster monitoring software must handle network interfaces, storage and database monitoring, and switching, including dependencies.