Chapter 17. Using the Stream Control Transmission Protocol (SCTP) on a bare metal cluster
As a cluster administrator, you can use the Stream Control Transmission Protocol (SCTP) on a cluster.
17.1. Support for Stream Control Transmission Protocol (SCTP) on OpenShift Container Platform
As a cluster administrator, you can enable SCTP on the hosts in the cluster. On Red Hat Enterprise Linux CoreOS (RHCOS), the SCTP module is disabled by default.
SCTP is a reliable message based protocol that runs on top of an IP network.
When enabled, you can use SCTP as a protocol with pods, services, and network policy. A Service
object must be defined with the type
parameter set to either the ClusterIP
or NodePort
value.
17.1.1. Example configurations using SCTP protocol
You can configure a pod or service to use SCTP by setting the protocol
parameter to the SCTP
value in the pod or service object.
In the following example, a pod is configured to use SCTP:
apiVersion: v1 kind: Pod metadata: namespace: project1 name: example-pod spec: containers: - name: example-pod ... ports: - containerPort: 30100 name: sctpserver protocol: SCTP
In the following example, a service is configured to use SCTP:
apiVersion: v1 kind: Service metadata: namespace: project1 name: sctpserver spec: ... ports: - name: sctpserver protocol: SCTP port: 30100 targetPort: 30100 type: ClusterIP
In the following example, a NetworkPolicy
object is configured to apply to SCTP network traffic on port 80
from any pods with a specific label:
kind: NetworkPolicy apiVersion: networking.k8s.io/v1 metadata: name: allow-sctp-on-http spec: podSelector: matchLabels: role: web ingress: - ports: - protocol: SCTP port: 80
17.2. Enabling Stream Control Transmission Protocol (SCTP)
As a cluster administrator, you can load and enable the blacklisted SCTP kernel module on worker nodes in your cluster.
Prerequisites
-
Install the OpenShift CLI (
oc
). -
Access to the cluster as a user with the
cluster-admin
role.
Procedure
Create a file named
load-sctp-module.yaml
that contains the following YAML definition:apiVersion: machineconfiguration.openshift.io/v1 kind: MachineConfig metadata: name: load-sctp-module labels: machineconfiguration.openshift.io/role: worker spec: config: ignition: version: 3.2.0 storage: files: - path: /etc/modprobe.d/sctp-blacklist.conf mode: 0644 overwrite: true contents: source: data:, - path: /etc/modules-load.d/sctp-load.conf mode: 0644 overwrite: true contents: source: data:,sctp
To create the
MachineConfig
object, enter the following command:$ oc create -f load-sctp-module.yaml
Optional: To watch the status of the nodes while the MachineConfig Operator applies the configuration change, enter the following command. When the status of a node transitions to
Ready
, the configuration update is applied.$ oc get nodes
17.3. Verifying Stream Control Transmission Protocol (SCTP) is enabled
You can verify that SCTP is working on a cluster by creating a pod with an application that listens for SCTP traffic, associating it with a service, and then connecting to the exposed service.
Prerequisites
-
Access to the internet from the cluster to install the
nc
package. -
Install the OpenShift CLI (
oc
). -
Access to the cluster as a user with the
cluster-admin
role.
Procedure
Create a pod starts an SCTP listener:
Create a file named
sctp-server.yaml
that defines a pod with the following YAML:apiVersion: v1 kind: Pod metadata: name: sctpserver labels: app: sctpserver spec: containers: - name: sctpserver image: registry.access.redhat.com/ubi9/ubi command: ["/bin/sh", "-c"] args: ["dnf install -y nc && sleep inf"] ports: - containerPort: 30102 name: sctpserver protocol: SCTP
Create the pod by entering the following command:
$ oc create -f sctp-server.yaml
Create a service for the SCTP listener pod.
Create a file named
sctp-service.yaml
that defines a service with the following YAML:apiVersion: v1 kind: Service metadata: name: sctpservice labels: app: sctpserver spec: type: NodePort selector: app: sctpserver ports: - name: sctpserver protocol: SCTP port: 30102 targetPort: 30102
To create the service, enter the following command:
$ oc create -f sctp-service.yaml
Create a pod for the SCTP client.
Create a file named
sctp-client.yaml
with the following YAML:apiVersion: v1 kind: Pod metadata: name: sctpclient labels: app: sctpclient spec: containers: - name: sctpclient image: registry.access.redhat.com/ubi9/ubi command: ["/bin/sh", "-c"] args: ["dnf install -y nc && sleep inf"]
To create the
Pod
object, enter the following command:$ oc apply -f sctp-client.yaml
Run an SCTP listener on the server.
To connect to the server pod, enter the following command:
$ oc rsh sctpserver
To start the SCTP listener, enter the following command:
$ nc -l 30102 --sctp
Connect to the SCTP listener on the server.
- Open a new terminal window or tab in your terminal program.
Obtain the IP address of the
sctpservice
service. Enter the following command:$ oc get services sctpservice -o go-template='{{.spec.clusterIP}}{{"\n"}}'
To connect to the client pod, enter the following command:
$ oc rsh sctpclient
To start the SCTP client, enter the following command. Replace
<cluster_IP>
with the cluster IP address of thesctpservice
service.# nc <cluster_IP> 30102 --sctp