12.11. Enabling multicast for a project
12.11.1. About multicast
With IP multicast, data is broadcast to many IP addresses simultaneously.
At this time, multicast is best used for low-bandwidth coordination or service discovery and not a high-bandwidth solution.
Multicast traffic between OpenShift Container Platform pods is disabled by default. If you are using the OpenShift SDN default Container Network Interface (CNI) network provider, you can enable multicast on a per-project basis.
When using the OpenShift SDN network plug-in in networkpolicy isolation mode:
-
Multicast packets sent by a pod will be delivered to all other pods in the project, regardless of
NetworkPolicyobjects. Pods might be able to communicate over multicast even when they cannot communicate over unicast. -
Multicast packets sent by a pod in one project will never be delivered to pods in any other project, even if there are
NetworkPolicyobjects that allow communication between the projects.
When using the OpenShift SDN network plug-in in multitenant isolation mode:
- Multicast packets sent by a pod will be delivered to all other pods in the project.
- Multicast packets sent by a pod in one project will be delivered to pods in other projects only if each project is joined together and multicast is enabled in each joined project.
12.11.2. Enabling multicast between pods
You can enable multicast between pods for your project.
Prerequisites
-
Install the OpenShift CLI (
oc). -
You must log in to the cluster with a user that has the
cluster-adminrole.
Procedure
Run the following command to enable multicast for a project. Replace
<namespace>with the namespace for the project you want to enable multicast for.$ oc annotate netnamespace <namespace> \ netnamespace.network.openshift.io/multicast-enabled=true
Verification
To verify that multicast is enabled for a project, complete the following procedure:
Change your current project to the project that you enabled multicast for. Replace
<project>with the project name.$ oc project <project>
Create a pod to act as a multicast receiver:
$ cat <<EOF| oc create -f - apiVersion: v1 kind: Pod metadata: name: mlistener labels: app: multicast-verify spec: containers: - name: mlistener image: registry.access.redhat.com/ubi8 command: ["/bin/sh", "-c"] args: ["dnf -y install socat hostname && sleep inf"] ports: - containerPort: 30102 name: mlistener protocol: UDP EOFCreate a pod to act as a multicast sender:
$ cat <<EOF| oc create -f - apiVersion: v1 kind: Pod metadata: name: msender labels: app: multicast-verify spec: containers: - name: msender image: registry.access.redhat.com/ubi8 command: ["/bin/sh", "-c"] args: ["dnf -y install socat && sleep inf"] EOFStart the multicast listener.
Get the IP address for the Pod:
$ POD_IP=$(oc get pods mlistener -o jsonpath='{.status.podIP}')To start the multicast listener, in a new terminal window or tab, enter the following command:
$ oc exec mlistener -i -t -- \ socat UDP4-RECVFROM:30102,ip-add-membership=224.1.0.1:$POD_IP,fork EXEC:hostname
Start the multicast transmitter.
Get the pod network IP address range:
$ CIDR=$(oc get Network.config.openshift.io cluster \ -o jsonpath='{.status.clusterNetwork[0].cidr}')To send a multicast message, enter the following command:
$ oc exec msender -i -t -- \ /bin/bash -c "echo | socat STDIO UDP4-DATAGRAM:224.1.0.1:30102,range=$CIDR,ip-multicast-ttl=64"If multicast is working, the previous command returns the following output:
mlistener
