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Verifying connectivity to an endpoint

The Cluster Network Operator (CNO) runs a controller, the connectivity check controller, that performs a connection health check between resources within your cluster.

By reviewing the results of the health checks, you can diagnose connection problems or eliminate network connectivity as the cause of an issue that you are investigating.

Connection health checks that are performed​

Establish TCP connections to target services, endpoints, and load balancers to verify that control plane components, routing layers, and node services can communicate without interruption.

To verify that cluster resources are reachable, a TCP connection is made to each of the following cluster API services:

  • Kubernetes API server service
  • Kubernetes API server endpoints
  • OpenShift API server service
  • OpenShift API server endpoints
  • Load balancers

To verify that services and service endpoints are reachable on every node in the cluster, a TCP connection is made to each of the following targets:

  • Health check target service
  • Health check target endpoints

Implementation of connection health checks​

The connectivity check controller orchestrates connection verification checks in your cluster. The results for the connection tests are stored in PodNetworkConnectivity objects in the openshift-network-diagnostics namespace. Connection tests are performed every minute in parallel.

The Cluster Network Operator (CNO) deploys several resources to the cluster to send and receive connectivity health checks:

Health check source
This program deploys in a single pod replica set managed by a Deployment object. The program consumes PodNetworkConnectivity objects and connects to the spec.targetEndpoint specified in each object.
Health check target
A pod deployed as part of a daemon set on every node in the cluster. The pod listens for inbound health checks. The presence of this pod on every node allows for the testing of connectivity to each node.

You can configure the nodes which network connectivity sources and targets run on with a node selector. Additionally, you can specify permissible tolerations for source and target pods. The configuration is defined in the singleton cluster custom resource of the Network API in the config.openshift.io/v1 API group.

Pod scheduling occurs after you have updated the configuration. Therefore, you must apply node labels that you intend to use in your selectors before updating the configuration. Labels applied after updating your network connectivity check pod placement are ignored.

Refer to the default configuration in the following YAML:

Default configuration for connectivity source and target pods
apiVersion: config.openshift.io/v1
kind: Network
metadata:
  name: cluster
spec:
  # ...
    networkDiagnostics: (1)
      mode: "All" (2)
      sourcePlacement: (3)
        nodeSelector:
          checkNodes: groupA
        tolerations:
        - key: myTaint
          effect: NoSchedule
          operator: Exists
      targetPlacement: (4)
        nodeSelector:
          checkNodes: groupB
        tolerations:
        - key: myOtherTaint
          effect: NoExecute
          operator: Exists

where:

spec.networkDiagnostics
Specifies the network diagnostics configuration. If a value is not specified or an empty object is specified, and spec.disableNetworkDiagnostics=true is set in the network.operator.openshift.io custom resource named cluster, network diagnostics are disabled. If set, this value overrides spec.disableNetworkDiagnostics=true.
spec.networkDiagnostics.mode
Specifies the diagnostics mode. The value can be the empty string, All, or Disabled. The empty string is equivalent to specifying All.
spec.networkDiagnostics.sourcePlacement
Optional: Specifies a selector for connectivity check source pods. You can use the nodeSelector and tolerations fields to further specify the sourceNode pods. These are optional for both source and target pods. You can omit them, use both, or use only one of them.
spec.networkDiagnostics.targetPlacement
Optional: Specifies a selector for connectivity check target pods. You can use the nodeSelector and tolerations fields to further specify the targetNode pods. These are optional for both source and target pods. You can omit them, use both, or use only one of them.

Configuring pod connectivity check placement​

As a cluster administrator, you can configure which nodes the connectivity check pods run by modifying the network.config.openshift.io object named cluster.

Prerequisites

  • Install the OpenShift CLI (oc).

Procedure

  1. Edit the connectivity check configuration by entering the following command: 
    $ oc edit network.config.openshift.io cluster
  2. In the text editor, update the networkDiagnostics stanza to specify the node selectors that you want for the source and target pods.
  3. Save your changes and exit the text editor.

Verification

  • Verify that the source and target pods are running on the intended nodes by entering the following command:

    $ oc get pods -n openshift-network-diagnostics -o wide
    Example output
    NAME                                    READY   STATUS    RESTARTS   AGE     IP           NODE                                        NOMINATED NODE   READINESS GATES
    network-check-source-84c69dbd6b-p8f7n   1/1     Running   0          9h      10.131.0.8   ip-10-0-40-197.us-east-2.compute.internal   <none>           <none>
    network-check-target-46pct              1/1     Running   0          9h      10.131.0.6   ip-10-0-40-197.us-east-2.compute.internal   <none>           <none>
    network-check-target-8kwgf              1/1     Running   0          9h      10.128.2.4   ip-10-0-95-74.us-east-2.compute.internal    <none>           <none>
    network-check-target-jc6n7              1/1     Running   0          9h      10.129.2.4   ip-10-0-21-151.us-east-2.compute.internal   <none>           <none>
    network-check-target-lvwnn              1/1     Running   0          9h      10.128.0.7   ip-10-0-17-129.us-east-2.compute.internal   <none>           <none>
    network-check-target-nslvj              1/1     Running   0          9h      10.130.0.7   ip-10-0-89-148.us-east-2.compute.internal   <none>           <none>
    network-check-target-z2sfx              1/1     Running   0          9h      10.129.0.4   ip-10-0-60-253.us-east-2.compute.internal   <none>           <none>

PodNetworkConnectivityCheck object fields​

The PodNetworkConnectivityCheck object fields are described in the following tables.

PodNetworkConnectivityCheck object fields

Field Type Description
metadata.name string The name of the object in the following format: <source>-to-<target>. The destination described by <target> includes one of following strings:

  • load-balancer-api-external
  • load-balancer-api-internal
  • kubernetes-apiserver-endpoint
  • kubernetes-apiserver-service-cluster
  • network-check-target
  • openshift-apiserver-endpoint
  • openshift-apiserver-service-cluster
metadata.namespace string The namespace that the object is associated with. This value is always openshift-network-diagnostics.
spec.sourcePod string The name of the pod where the connection check originates, such as network-check-source-596b4c6566-rgh92.
spec.targetEndpoint string The target of the connection check, such as api.devcluster.example.com:6443.
spec.tlsClientCert object Configuration for the TLS certificate to use.
spec.tlsClientCert.name string The name of the TLS certificate used, if any. The default value is an empty string.
status object An object representing the condition of the connection test and logs of recent connection successes and failures.
status.conditions array The latest status of the connection check and any previous statuses.
status.failures array Connection test logs from unsuccessful attempts.
status.outages array Connect test logs covering the time periods of any outages.
status.successes array Connection test logs from successful attempts.

The following table describes the fields for objects in the status.conditions array:

status.conditions

FieldTypeDescription
lastTransitionTimestringThe time that the condition of the connection transitioned from one status to another.
messagestringThe details about last transition in a human readable format.
reasonstringThe last status of the transition in a machine readable format.
statusstringThe status of the condition.
typestringThe type of the condition.

The following table describes the fields for objects in the status.conditions array:

status.outages

FieldTypeDescription
endstringThe timestamp from when the connection failure is resolved.
endLogsarrayConnection log entries, including the log entry related to the successful end of the outage.
messagestringA summary of outage details in a human readable format.
startstringThe timestamp from when the connection failure is first detected.
startLogsarrayConnection log entries, including the original failure.

Connection log fields​

The fields for a connection log entry are described in the following table. The object is used in the following fields:

  • status.failures[]
  • status.successes[]
  • status.outages[].startLogs[]
  • status.outages[].endLogs[]

Connection log object

FieldTypeDescription
latencystringRecords the duration of the action.
messagestringProvides the status in a human readable format.
reasonstringProvides the reason for status in a machine readable format. The value is one of TCPConnect, TCPConnectError, DNSResolve, DNSError.
successbooleanIndicates if the log entry is a success or failure.
timestringThe start time of connection check.

Verifying network connectivity for an endpoint​

As a cluster administrator, you can verify the connectivity of an endpoint, such as an API server, load balancer, service, or pod, and verify that network diagnostics is enabled.

Prerequisites

  • Install the OpenShift CLI (oc).
  • Access to the cluster as a user with the cluster-admin role.

Procedure

  1. Confirm that network diagnostics are enable by entering the following command:

    $ oc get network.config.openshift.io cluster -o yaml
    Example output
      # ...
      status:
      # ...
        conditions:
        - lastTransitionTime: "2024-05-27T08:28:39Z"
          message: ""
          reason: AsExpected
          status: "True"
          type: NetworkDiagnosticsAvailable

  2. List the current PodNetworkConnectivityCheck objects by entering the following command:

    $ oc get podnetworkconnectivitycheck -n openshift-network-diagnostics
    Example output
    NAME                                                                                                                                AGE
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0   75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-1   73m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-2   75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-kubernetes-apiserver-service-cluster                               75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-kubernetes-default-service-cluster                                 75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-load-balancer-api-external                                         75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-load-balancer-api-internal                                         75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-network-check-target-ci-ln-x5sv9rb-f76d1-4rzrp-master-0            75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-network-check-target-ci-ln-x5sv9rb-f76d1-4rzrp-master-1            75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-network-check-target-ci-ln-x5sv9rb-f76d1-4rzrp-master-2            75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-network-check-target-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh      74m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-network-check-target-ci-ln-x5sv9rb-f76d1-4rzrp-worker-c-n8mbf      74m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-network-check-target-ci-ln-x5sv9rb-f76d1-4rzrp-worker-d-4hnrz      74m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-network-check-target-service-cluster                               75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-openshift-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0    75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-openshift-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-1    75m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-openshift-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-2    74m
    network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-openshift-apiserver-service-cluster                                75m

  3. View the connection test logs:

    1. From the output of the previous command, identify the endpoint that you want to review the connectivity logs for.

    2. View the object by entering the following command:

      $ oc get podnetworkconnectivitycheck <name> \
        -n openshift-network-diagnostics -o yaml

      where <name> specifies the name of the PodNetworkConnectivityCheck object.

      Example output
      apiVersion: controlplane.operator.openshift.io/v1alpha1
      kind: PodNetworkConnectivityCheck
      metadata:
        name: network-check-source-ci-ln-x5sv9rb-f76d1-4rzrp-worker-b-6xdmh-to-kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0
        namespace: openshift-network-diagnostics
        ...
      spec:
        sourcePod: network-check-source-7c88f6d9f-hmg2f
        targetEndpoint: 10.0.0.4:6443
        tlsClientCert:
          name: ""
      status:
        conditions:
        - lastTransitionTime: "2021-01-13T20:11:34Z"
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnectSuccess
          status: "True"
          type: Reachable
        failures:
        - latency: 2.241775ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: failed
            to establish a TCP connection to 10.0.0.4:6443: dial tcp 10.0.0.4:6443: connect:
            connection refused'
          reason: TCPConnectError
          success: false
          time: "2021-01-13T20:10:34Z"
        - latency: 2.582129ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: failed
            to establish a TCP connection to 10.0.0.4:6443: dial tcp 10.0.0.4:6443: connect:
            connection refused'
          reason: TCPConnectError
          success: false
          time: "2021-01-13T20:09:34Z"
        - latency: 3.483578ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: failed
            to establish a TCP connection to 10.0.0.4:6443: dial tcp 10.0.0.4:6443: connect:
            connection refused'
          reason: TCPConnectError
          success: false
          time: "2021-01-13T20:08:34Z"
        outages:
        - end: "2021-01-13T20:11:34Z"
          endLogs:
          - latency: 2.032018ms
            message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0:
              tcp connection to 10.0.0.4:6443 succeeded'
            reason: TCPConnect
            success: true
            time: "2021-01-13T20:11:34Z"
          - latency: 2.241775ms
            message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0:
              failed to establish a TCP connection to 10.0.0.4:6443: dial tcp 10.0.0.4:6443:
              connect: connection refused'
            reason: TCPConnectError
            success: false
            time: "2021-01-13T20:10:34Z"
          - latency: 2.582129ms
            message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0:
              failed to establish a TCP connection to 10.0.0.4:6443: dial tcp 10.0.0.4:6443:
              connect: connection refused'
            reason: TCPConnectError
            success: false
            time: "2021-01-13T20:09:34Z"
          - latency: 3.483578ms
            message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0:
              failed to establish a TCP connection to 10.0.0.4:6443: dial tcp 10.0.0.4:6443:
              connect: connection refused'
            reason: TCPConnectError
            success: false
            time: "2021-01-13T20:08:34Z"
          message: Connectivity restored after 2m59.999789186s
          start: "2021-01-13T20:08:34Z"
          startLogs:
          - latency: 3.483578ms
            message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0:
              failed to establish a TCP connection to 10.0.0.4:6443: dial tcp 10.0.0.4:6443:
              connect: connection refused'
            reason: TCPConnectError
            success: false
            time: "2021-01-13T20:08:34Z"
        successes:
        - latency: 2.845865ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnect
          success: true
          time: "2021-01-13T21:14:34Z"
        - latency: 2.926345ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnect
          success: true
          time: "2021-01-13T21:13:34Z"
        - latency: 2.895796ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnect
          success: true
          time: "2021-01-13T21:12:34Z"
        - latency: 2.696844ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnect
          success: true
          time: "2021-01-13T21:11:34Z"
        - latency: 1.502064ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnect
          success: true
          time: "2021-01-13T21:10:34Z"
        - latency: 1.388857ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnect
          success: true
          time: "2021-01-13T21:09:34Z"
        - latency: 1.906383ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnect
          success: true
          time: "2021-01-13T21:08:34Z"
        - latency: 2.089073ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnect
          success: true
          time: "2021-01-13T21:07:34Z"
        - latency: 2.156994ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnect
          success: true
          time: "2021-01-13T21:06:34Z"
        - latency: 1.777043ms
          message: 'kubernetes-apiserver-endpoint-ci-ln-x5sv9rb-f76d1-4rzrp-master-0: tcp
            connection to 10.0.0.4:6443 succeeded'
          reason: TCPConnect
          success: true
          time: "2021-01-13T21:05:34Z"