What action can be taken if a Splunk indexer fails?

Redirecting data to the remaining indexers in the cluster is the correct action to take if a Splunk indexer fails. In a clustered indexing environment, other indexers can take over the data ingestion responsibilities when one indexer goes down. This ensures that data continues to be ingested without significant disruption to the system. This functionality helps maintain high availability and reliability of data processing in Splunk environments.

Increasing data retention limits or stopping all incoming data may not effectively resolve the issue of a failed indexer, as they do not address the root cause of the failure or ensure continuity of data ingestion. Additionally, automatically switching to a single-point index server could lead to single points of failure, negating the benefits of using a clustered architecture. Thus, utilizing the existing resources in the cluster to manage data processing is the most effective response in this scenario.