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All highly available systems include at least one facility to monitor the health of components within the system. Such health monitors are often used as inputs to distributed coordination systems (such as etcd, zookeeper, or consul) and monitoring systems (such as nagios or zabbix). Within ONAP Consul is the monitoring system of choice and deployed by OOM in two parts. A three-way, centralized Consul server cluster is deployed as a highly available monitor of all of the ONAP components. The Consul server provides an user interface that allows a user to graphically view the current health status of all of the ONAP components for which agents have been created - a sample from the ONAP Integration labs follows. Monitoring of ONAP components is configured in the agents within JSON files and stored in gerrit under the consul-agent-config.
Initially the Consul agents are using the same health monitoring facilities as the robot test infrastructure which are typically just validating that the end-point if reachable. Some health checks already support more advanced checking - such as validating that a database is able to create, update and delete an entry. Consul exposes an API that allows external agents to use the results of the health check such as the Kubernetes "liveness" probes described below.
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