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The usage pattern echoes a common resiliency pattern in ONAP wherein each component is replicated within the site and across sites.
For geo-redundant state persistence the ONAP component can directly use the REST API provided by MUSIC in CHAP (like ONAP HAS does now). However, if it currently uses a database for state persistence, then it can use the mdbc driver which will intercept its local calls to its database and copy it to MUSIC. This is shown in the second figure for how MSO, which maintains state in a H2 database may use it.
Each ONAP component replicas runs a companion HAL daemon (halD) that provides health checks, failure detection and failover as mentioned before.
General Usage:
A specific example:
Another prism through which one can view CHAP is that it enables ONAP components to achieve carrier grade requirements of reliability as shown in the following figure:
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