JIRA 7.1.0 added a new endpoint that can be accessed at http://<base_url>/status which displays a simple output when it is running:

{"state":"RUNNING"}

This URL is useful for monitoring systems to quickly check whether JIRA is up and running. This works in both Server and Data Center versions, but is especially useful in multi-node Data Center deployments so that a load balancer knows when remove a particular node from the pool.

There is some documentation on the JIRA DC (under "Load Balancing Health Check URL") page but it should call out the various statuses, like was done for Confluence (https://jira.atlassian.com/browse/CONF-41395) - https://confluence.atlassian.com/enterprise/confluence-data-center-technical-overview-612959401.html