With the release of NiFi 1.8.0, flowfiles that remain on a disconnected node can be rebalanced to other active nodes in the cluster via offloading.
Note: This tutorial assumes you have already setup a running NiFi cluster. The examples included are for a 2 node NiFi cluster.
This tutorial was tested using the following environment and components:
First, generate some queued flowfiles:
In the Global Menu at the top left, select "Cluster" to see the Cluster Management dialog:
The queued flowfiles are distributed between both nodes in the cluster:
Select Disconnect for one of the nodes:
The node is disconnected:
Select Offload () on the disconnected node. This will stop and terminate all processors and rebalance flowfiles to the other connected nodes in the cluster:
Note: Offload would also stop transmitting on all remote process groups if they were in the flow.
When offloading is finished, all of the queued flowfiles are now on the active node:
An offloaded node can be either connected back to the cluster or deleted. Select Delete:
Once deleted, the node cannot be rejoined to the cluster until it has been restarted. To decommission the node, stop/remove the NiFi service on the host.