Design Principles

Pod level management

NiFi is a stateful application. The first piece of the puzzle is the Node, which is a simple server capable of createing/forming a cluster with other Nodes. Every Node has his own unique configuration which differs slightly from all others.

All NiFi on Kubernetes setup use StatefulSet to create a NiFi Cluster. Just to quickly recap from the K8s docs:

StatefulSet manages the deployment and scaling of a set of Pods, and provide guarantees about their ordering and uniqueness. Like a Deployment, a StatefulSet manages Pods that are based on an identical container spec. Unlike a Deployment, a StatefulSet maintains sticky identities for each of its Pods. These pods are created from the same spec, but are not interchangeable: each has a persistent identifier that is maintained across any rescheduling.

How does this looks from the perspective of Apache NiFi ?

With StatefulSet we get:

• unique Node IDs generated during Pod startup
• networking between Nodes with headless services
• unique Persistent Volumes for Nodes

Using StatefulSet we lose the ability to:

• modify the configuration of unique Nodes
• remove a specific Node from a cluster (StatefulSet always removes the most recently created Node)
• use multiple, different Persistent Volumes for each Node

The NiFi Operator uses simple Pods, ConfigMaps, and PersistentVolumeClaims, instead of StatefulSet (based on the design used by Banzai Cloud Kafka Operator). Using these resources allows us to build an Operator which is better suited to NiFi.

With the NiFi operator we can:

• modify the configuration of unique Nodes
• remove specific Nodes from clusters
• use multiple Persistent Volumes for each Node