Unidirectional flow of messages on a topic in two Cluster

[Hitesh-Agrawal]

Observed behavior

I have two NATS Clusters each with 4 Node.
ClusterA
node1a.cluster.svc.local
node2a.cluster.svc.local
node3a.cluster.svc.local
node4a.cluster.svc.local
Load Balancer :- clustera.lb.internal.com

ClusterB
node1b.cluster.svc.local
node2b.cluster.svc.local
node3b.cluster.svc.local
node4b.cluster.svc.local
Load Balancer :- clusterb.lb.internal.com

I want messages generated in Cluster A on any topic to flow to ClusterB ( if there is interest for the topic), but not vice-versa.

I have configured 1 nodes in ClusterA (node1a.cluster.svc.local) with
leafnodes {
listen: 0.0.0.0:7222
}

=================
In ClusterB only 1 node (node1b.cluster.svc.local) is configured with leaf remote as follow
listen: 0.0.0.0:4222
http: 0.0.0.0:8222

cluster {
listen: 0.0.0.0:5222
name: ClusterB

routes = [
nats-route://node2b.cluster.svc.local:5222
nats-route://node3b.cluster.svc.local:5222
nats-route://node4b.cluster.svc.local:5222
]

no_advertise: true
connect_retries: 0
cluster_advertise: node1b.cluster.svc.local:5222
}
leafnodes {
remotes = [
{
urls: [
"nats-leaf://node1a.cluster.svc.local:7422",
]
deny_exports = [">"]
},
]
}

logtime: true
max_connections: 65535
max_control_line: 512
max_payload: 1048576
max_pending: 67108864
write_deadline: "2s"

=====================================================

Expected behavior

When a message is pub on "testtopic" in cluster "A",
nats pub testtopic "Test from cluster A" --server nats://clustera.lb.internal.com
07:27:03 Published 23 bytes to "testtopic"

It should be received on all the 4 nodes in cluster "B"

but its received only on node1b.cluster.svc.local
nats sub testtopic --server nats://node1b.cluster.svc.local
07:26:38 Subscribing on testtopic
[#1] Received on "testtopic"
Test from cluster A

When I do
nats sub testtopic --server nats://node2b.cluster.svc.local

I dont receive anything here

======================================
Expected Behaviour
Messages published by any node in "Cluster A" , should be receivable on all the nodes in "Cluster B"

The message received on node1b.cluster.svc.local from remote leaf "node1a.cluster.svc.local" should be forwarded to all nodes (node{2-4}b) in "Cluster B".

Question:
Do I need to configure all the nodes in cluster B as a leafnode to "nats-leaf://node1a.cluster.svc.local:7422" ?
I think node1b.cluster.svc.local should have acted as a forwarded for any interest generated in local clusterB for topic "testtopic"
I cannot remove
deny_exports = [">"] as I do not want any messages generated in ClusterB to flow to ClusterA.

Server and client version

[60] 2024/10/24 06:00:12.354477 [INF] Starting nats-server
[60] 2024/10/24 06:00:12.354522 [INF] Version: 2.3.4

Host environment

EKS Kubernetes v1.29

Steps to reproduce

Configure your clusters as above and test the same.

[Hitesh-Agrawal]

Just to add,
I want node1b.cluster.svc.local to act as an 1 way bridge between "Cluster A" and "Cluster B". Only node1b.cluster.svc.local can reach node1a.cluster.svc.local:7222 other nodes in "Cluster B" cannot reach Cluster A.

Message flow should be "Cluster A" -> node1a.cluster.svc.local:7222 -> node1b.cluster.svc.local -> All nodes in "Cluster B"
If there is any other solution in place , I would be happy to explore that.