Search should always run on a separate environment from your Liferay DXP server. Liferay DXP supports Elasticsearch, and Solr. Both can also be clustered.
For more information on how to cluster Elasticsearch, see Elasticsearch’s distributed cluster setup.
Once Liferay DXP servers have been properly configured as a cluster and the same for Elasticsearch, change Liferay DXP from embedded mode to remote mode. On the first connection, the two sets of clustered servers communicate with each other the list of all IP addresses; in case of a node going down, the proper failover protocols enable. Queries and indexes can continue to be sent for all nodes.
For more information on how to cluster Solr, see Apache Solr Cloud documentation.
Once Liferay DXP servers have been properly configured as a cluster, deploy the Liferay Connector to Solr on all nodes. (This app is available for download from Liferay Marketplace) Create a Solr Cloud (cluster) managed by Apache Solr Zookeeper. Connect the Liferay DXP cluster to Zookeeper and finish the final configurations to connect the two clusters.