Managing large-scale Splunk environments requires a strong understanding of both licensing control and cluster management. License Master and Cluster Master are two core components that play very different but equally critical roles in Splunk architecture. Interviewers often test how well candidates understand these roles, how they interact with indexers, and how they support scalability and high availability.
This blog explains License Master and Cluster Master concepts in a simple, interview-focused way. The questions are designed to reflect real-world Splunk admin scenarios rather than textbook definitions. If you are preparing for Splunk architecture or platform administration interviews, this guide will help you explain concepts clearly and confidently.
License Master and Cluster Master Interview Questions and Answers
Question 1: What is the License Master in Splunk?
Answer: The license master is the component responsible for enforcing licensing control in Splunk. It tracks how much data is indexed across the environment and ensures usage stays within licensed limits.
Question 2: Which Splunk components report to the License Master?
Answer: Indexers and heavy forwarders report their indexed data volume to the license master. Search heads do not contribute to license usage.
Question 3: How does the License Master calculate daily license usage?
Answer: Each license slave reports the number of bytes indexed. The license master aggregates this data to calculate total daily usage.
Example internal search:
index=_internal source=*license_usage.log
| stats sum(b) as total_bytes by idx
Question 4: What happens when license usage exceeds the limit?
Answer: Splunk records a license violation. Indexing continues, but persistent violations restrict searching on non-internal indexes until compliance is restored.
Question 5: Does a license violation stop data ingestion?
Answer: Data ingestion and indexing continue. Only search access is restricted after repeated violations.
Question 6: What is a license pool?
Answer: A license pool allows administrators to allocate portions of the total license to specific indexers or groups. This helps control ingestion by application or team.
Question 7: How is an indexer connected to the License Master?
Answer: Indexers are configured to point to the license master using the management port.
Example configuration:
[license]
master_uri = https://license-master:8089
Question 8: Can an environment have multiple License Masters?
Answer: Only one active license master is supported in a Splunk deployment.
Question 9: What is the Cluster Master in Splunk?
Answer: The cluster master manages indexer clustering. It controls bucket replication, search availability, and overall cluster health.
Question 10: Does the Cluster Master store indexed data?
Answer: The cluster master does not store data. It only manages how data is replicated and distributed across indexers.
Question 11: What is indexer clustering?
Answer: Indexer clustering is a mechanism that provides high availability and fault tolerance by maintaining multiple copies of indexed data across indexers.
Question 12: What is the replication factor?
Answer: Replication factor defines how many total copies of each bucket exist across the cluster.
Question 13: What is the search factor?
Answer: Search factor defines how many searchable copies of data must be available to support searches even during failures.
Question 14: How do replication factor and search factor support high availability?
Answer: They ensure that data remains searchable even if one or more indexers become unavailable.
Question 15: How does an indexer join an indexer cluster?
Answer: Indexers are configured as cluster peers and connect to the cluster master.
Example configuration:
[clustering]
mode = peer
master_uri = https://cluster-master:8089
replication_port = 9887
Question 16: What is a bucket fix-up?
Answer: A bucket fix-up is the automatic process where the cluster master re-replicates buckets to meet replication or search factor requirements.
Question 17: How does the Cluster Master monitor cluster health?
Answer: It tracks peer status, bucket counts, and replication levels using internal metrics and logs.
Example search:
index=_internal source=*clustering.log
| stats count by component
Question 18: Can the Cluster Master also act as an indexer?
Answer: The cluster master should be a dedicated node to avoid performance and stability issues.
Question 19: How do search heads interact with indexer clusters?
Answer: Search heads rely on the cluster master to ensure searchable copies exist. They distribute searches across available peers automatically.
Question 20: What is the difference between License Master and Cluster Master?
Answer: The license master manages data volume and compliance. The cluster master manages data availability and redundancy. They serve entirely different purposes.
Conclusion
License Master and Cluster Master are foundational components in Splunk architecture. While the license master ensures data ingestion stays within licensed limits, the cluster master ensures indexed data remains highly available and searchable. Understanding how these components interact with indexers, search heads, and internal processes is essential for any Splunk administrator.
For interviews, focus on explaining responsibilities, configuration logic, and real-world scenarios rather than memorizing definitions. Clear reasoning and architectural understanding matter more than terminology.
