Options are not available to configure while selecting the "Remote Cluster Connection ID"

Issue

• After portal upgrade, when updating the elastic search in DXP 7.3, options are not available to configure while selecting the "Remote Cluster Connection ID". And the below error triggers at the same time span when this activity is performed.

• 2021-09-15 01:57:37.319 ERROR [liferay/scheduler_dispatch-2][ElasticsearchIndexSearcher:165] java.lang.RuntimeException: org.elasticsearch.ElasticsearchStatusException: ElasticsearchStatusException[Elasticsearch exception [type=search_phase_execution_exception, reason=all shards failed]]; nested: ElasticsearchException[Elasticsearch exception [type=illegal_argument_exception, reason=Text fields are not optimised for operations that require per-document field data like aggregations and sorting, so these operations are disabled by default. Please use a keyword field instead. Alternatively, set fielddata=true on [ratings] in order to load field data by uninverting the inverted index. Note that this can use significant memory.]]; nested: ElasticsearchException[Elasticsearch exception [type=illegal_argument_exception, reason=Text fields are not optimised for operations that require per-document field data like aggregations and sorting, so these operations are disabled by default. Please use a keyword field instead. Alternatively, set fielddata=true on [ratings] in order to load field data by uninverting the inverted index. Note that this can use significant memory.]];

Environment

• Liferay DXP 7.3
• ES 7

Resolution

• Post upgrade of the Liferay DXP, there are additional steps to upgrade the search experience. Please go through the Liferay document "Upgrading Search for Liferay 7.3" which describes the prerequisites, configuration, things to be considered, best practices, and so on as the configurations steps depend on your existing search engine installation and Liferay version. 
  

  Note: Please ensure you’ll always want to start by backing up your existing indexes.

• Secondly, Post upgrade, if you have disabled search indexing, the Re-indexing search indexes are required for most upgrades but are typically not required for a few situations like applying an SP or upgrading to a new GA (rolling release) within the same Liferay version. Hence, execute the full re-index of all search indexes after backing up your existing indexes.
• Steps to reindex as above suggested:

• Click on theGlobal Menu Navigate to Control Panel -> Configuration -> Search -> click on index actions tab Execute button next to the option "Reindex all search indexes". Once it's done, displays a success message.

Additional Information

• On a side note: Liferay 7.3 supports only Elasticsearch 7.9+ via the out-of-the-box Liferay Connector to Elasticsearch 7. It is very important to go through the high-level steps required to navigate safely from your existing stack to the Liferay 7.3 stack. Please go through the child pages of the article Upgrading Search for Liferay 7.3 for the complete reference.
• Complete references:
  • Post-Upgrade Considerations
  • Elasticsearch Connector Configuration Reference
  • Please go through the Search Engine Compatibility Matrix for details on the compatible Elasticsearch versions, available Liferay connectors, and required Liferay patch levels.
  • https://learn.liferay.com/dxp/latest/en/using-search/installing-and-upgrading-a-search-engine/elasticsearch/troubleshooting-elasticsearch-installation.html
  • https://help.liferay.com/hc/en-us/articles/4407485139085-Field-data-is-disabled-on-text-fields-by-default when commerce activated.