What is a Headless Service and why is it used with StatefulSet?

A Headless Service in Kubernetes is a service without a dedicated IP address and without a load balancer. Instead, it creates DNS records for each Pod associated with this service.

When a Headless Service is used together with a StatefulSet, it allows each Pod to have a stable network name and address, which is important for applications that require persistent identification and direct interaction between instances (e.g., databases, clusters).

Thus, a Headless Service provides:

• Persistent DNS names for each Pod in the StatefulSet
• The ability to directly address a specific Pod
• Support for network interactions requiring stable identification

Example: in a Cassandra cluster, each node must be accessible via a unique DNS name, which is achieved using a Headless Service and a StatefulSet.