Confluent for Kubernetes Networking

This section of documents describes the networking options you can configure in Confluent for Kubernetes (CFK) to expose Kafka and other Confluent Platform components to clients.

Confluent Platform networking interfaces

The following images show the networking interfaces available for Confluent Platform components.

_images/20210428-Connect_Networking_Architecture.png _images/20210428-Schema_Registry_Networking_Architecture.png _images/20210428-ksqlDB-Networking-Architecture.png _images/20210428-Control_Center_Networking_Architecture.png

Confluent Platform external interfaces

The following shows the high level overview of external interfaces to connect to Confluent components from outside the Kubernetes cluster.


Kafka listeners

Listeners are the interfaces that Kafka binds to. Advertised listeners are how clients and components can connect to Kafka.

A Kafka listener is configured by providing a hostname, port, and security protocol.

CFK allows you to configure listeners in flexible ways while providing the same default configurations out of the box. To facilitate that, CFK organizes listeners into the following categories in Kafka custom resources (CRs):

Internal listener

Within the same Kubernetes cluster, Confluent components deployed by CFK and client applications connect to Kafka over Kafka’s internal listener at the following addresses:

  • If Kafka cluster is deployed to the same namespace as this client / component: <kafka-component-name>:9071
  • If Kafka cluster is deployed to a different namespace as this client / component: <kafka-component-name>.<kafka-namespace>.svc.cluster.local:9071
External listener

Clients external to the Kubernetes network connect to Confluent Platform components using the external listener, with the default port 9092.

The following are the external access methods CFK supports. You can configure each component with one method, and once you enable external access one method and deploy Confluent, you cannot change to another external access method.

  • Load balancers

    Clients connect to Confluent Platform using the Kubernetes provider’s load balancer.

  • Node ports

    Clients connect to Confluent Platform at specified static ports (the NodePort) on the Kubernetes worker node (or via customer-managed networking infrastructure that can forward traffic to those ports).

  • Port-based static access

    A Kubernetes Ingress controller manages clients’ connection to Kafka using port-based routing.

  • Host-based static access

    A Kubernetes Ingress controller manages clients’ connection to Kafka using host-based routing.

  • Routes (for OpenShift)

    Clients connect to Confluent Platform using OpenShift routes.

Custom listeners

In addition to external and internal access listeners, you can configure additional custom listeners to access Kafka, for example, to have a separate networking channel for sets of clients.

You can specify a port number that is greater than 9092. 9092 and lower port numbers are reserved by CFK.

The name of a custom listener is case-insensitive.

See Kafka custom listeners for a sample scenario for setting up custom Kafka listeners.

Replication listener

The replication listener is used for inter-broker communication.

To override the inter-broker listener to be another type of listener, for example, the internal listener, set the following Kafka property using the configOverride feature.

In CFK, you can configure the following for each Kafka listener:

Access ksqlDB from Confluent Control Center

When Confluent Control Center and ksqlDB are deployed and run inside of a Kubernetes cluster, the components communicate with each other using their internal endpoints (svc.local). And when you connect to the Confluent Control Center in a browser outside of the Kubernetes cluster, Confluent Control Center forwards the browser to ksqlDB and provides the browser with the internal endpoint of the ksqlDB. The internal endpoint is likely inaccessible to the browser, and the data will not flow between the browser and the ksqlDB cluster.

If your ksqlDB cluster is configured with an external endpoint via a load balancer, a node port, or a route, specify the advertisedUrl in the Confluent Control Center CR to use the ksqlDB external endpoint for browser connections:

kind: ConrolCenter