When I downgraded Elasticsearch 7.10 to 7.6, I was not able to restart the elasticsearch service and was facing these errors: and “Format version is not supported” After diagnosing the issue and going through a number of web URLs, I come to know that the following line in the elasticsearch.yml file will fix my issue. cluster.initial_master_nodes: ["x.x.x.x"] OR cluster.initial_master_nodes: master - node - a I hope it will help someone and save their time too. Thanks!!! Enjoy Programming!! :)