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Managing nodes

Overview

You can manage nodes in your instance using the CLI.

When you perform node management operations, the CLI interacts with node objects that are representations of actual node hosts. The master uses the information from node objects to validate nodes with health checks.

Listing nodes

To list all nodes that are known to the master:

$ oc get nodes
NAME                   STATUS    ROLES     AGE       VERSION
master.example.com     Ready     master    7h        v1.9.1+a0ce1bc657
node1.example.com      Ready     compute   7h        v1.9.1+a0ce1bc657
node2.example.com      Ready     compute   7h        v1.9.1+a0ce1bc657

To only list information about a single node, replace <node> with the full node name:

$ oc get node <node>

The STATUS column in the output of these commands can show nodes with the following conditions:

Table 1. Node Conditions
Condition Description

Ready

The node is passing the health checks performed from the master by returning StatusOK.

NotReady

The node is not passing the health checks performed from the master.

SchedulingDisabled

Pods cannot be scheduled for placement on the node.
The STATUS column can also show Unknown for a node if the CLI cannot find any node condition.

To get more detailed information about a specific node, including the reason for the current condition:

$ oc describe node <node>

For example:

$ oc describe node node1.example.com

Name:               node1.example.com (1)
Roles:              master (2)
Labels:             beta.kubernetes.io/arch=amd64 (3)
                    beta.kubernetes.io/os=linux
                    glusterfs=storage-host
                    kubernetes.io/hostname=node1.example.com
                    node-role.kubernetes.io/master=true
                    region=infra
                    zone=default
Annotations:        volumes.kubernetes.io/controller-managed-attach-detach=true (4)
Taints:             <none> (5)
CreationTimestamp:  Sat, 07 Apr 2018 16:49:31 +0530
Conditions:                                                    (6)
  Type             Status  LastHeartbeatTime                 LastTransitionTime                Reason                       Message
  ----             ------  -----------------                 ------------------                ------                       -------
  OutOfDisk        False   Wed, 30 May 2018 14:19:56 +0530   Sat, 07 Apr 2018 16:49:31 +0530   KubeletHasSufficientDisk     kubelet has sufficient disk space available
  MemoryPressure   False   Wed, 30 May 2018 14:19:56 +0530   Sat, 07 Apr 2018 16:49:31 +0530   KubeletHasSufficientMemory   kubelet has sufficient memory available
  DiskPressure     False   Wed, 30 May 2018 14:19:56 +0530   Sat, 07 Apr 2018 16:49:31 +0530   KubeletHasNoDiskPressure     kubelet has no disk pressure
  Ready            True    Wed, 30 May 2018 14:19:56 +0530   Fri, 11 May 2018 15:09:42 +0530   KubeletReady                 kubelet is posting ready status
Addresses:                           (7)
  InternalIP:  10.74.2.51
  Hostname:    node1.example.com
Capacity:                            (8)
 cpu:     2
 memory:  16208764Ki
 pods:    20
Allocatable:
 cpu:     2
 memory:  16106364Ki
 pods:    20
System Info: (9)
 Machine ID:                 edd6dd9a8530d2c8c442c2d4e7f
 System UUID:                EDD6DD9A-853BD2C-8C442C2D4E7F
 Boot ID:                    750641e2-1b5b02b-ee068821264e
 Kernel Version:             3.10.0-693.el7.x86_64
 OS Image:                   OpenShift Enterprise
 Operating System:           linux
 Architecture:               amd64
 Container Runtime Version:  docker://1.13.1
 Kubelet Version:            v1.9.1+a0ce1bc657
 Kube-Proxy Version:         v1.9.1+a0ce1bc657
ExternalID:                  vm252-51.example.com
Non-terminated Pods:         (6 in total)           (10)
  Namespace                  Name                              CPU Requests  CPU Limits  Memory Requests  Memory Limits
  ---------                  ----                              ------------  ----------  ---------------  -------------
  default                    docker-registry-1-prph7           100m (5%)     0 (0%)      256Mi (1%)       0 (0%)
  default                    router-1-z625j                    100m (5%)     0 (0%)      256Mi (1%)       0 (0%)
  glusterfs                  glusterfs-storage-8h59h           100m (5%)     0 (0%)      100Mi (0%)       0 (0%)
  openshift-metrics          prometheus-0                      1 (50%)       1 (50%)     1Gi (6%)         1Gi (6%)
  openshift-metrics          prometheus-node-exporter-j5hbp    100m (5%)     200m (10%)  30Mi (0%)        50Mi (0%)
  openshift-web-console      webconsole-6c488985dd-4txcz       100m (5%)     0 (0%)      100Mi (0%)       0 (0%)
Allocated resources:
  (Total limits may be over 100 percent, i.e., overcommitted.)
  CPU Requests  CPU Limits   Memory Requests  Memory Limits
  ------------  ----------   ---------------  -------------
  1500m (75%)   1200m (60%)  1766Mi (11%)     1074Mi (6%)
Events:         <none>
1 The name of the node.
2 The role of the node, either master or compute.
3 The labels applied to the node.
4 The annotations applied to the node.
5 The taints applied to the node.
6 Node conditions.
7 The IP address and host name of the node.
8 The pod resources and allocatable resources.
9 Information about the node host.
10 The pods on the node.

Viewing nodes

You can display usage statistics about nodes, which provide the runtime environments for containers. These usage statistics include CPU, memory, and storage consumption.

To view the usage statistics:

$ oc adm top nodes
NAME       CPU(cores)   CPU%      MEMORY(bytes)   MEMORY%
node-1     297m         29%       4263Mi          55%
node-0     55m          5%        1201Mi          15%
infra-1    85m          8%        1319Mi          17%
infra-0    182m         18%       2524Mi          32%
master-0   178m         8%        2584Mi          16%

To view the usage statistics for nodes with labels:

$ oc adm top node --selector=''

You must choose the selector (label query) to filter on. Supports =, ==, and !=.

You must have cluster-reader permission to view the usage statistics.

Metrics must be installed to view the usage statistics.

Adding nodes

To add nodes to your existing OpenShift Container Platform cluster, you can run an Ansible playbook that handles installing the node components, generating the required certificates, and other important steps. See the advanced installation method for instructions on running the playbook directly.

Alternatively, if you used the quick installation method, you can re-run the installer to add nodes, which performs the same steps.

Deleting nodes

When you delete a node using the CLI, the node object is deleted in Kubernetes, but the pods that exist on the node itself are not deleted. Any bare pods not backed by a replication controller would be inaccessible to OpenShift Container Platform, pods backed by replication controllers would be rescheduled to other available nodes, and local manifest pods would need to be manually deleted.

To delete a node from the OpenShift Container Platform cluster:

  1. Evacuate pods from the node you are preparing to delete.

  2. Delete the node object:

    $ oc delete node <node>

  3. Check that the node has been removed from the node list:

    $ oc get nodes

    Pods should now be only scheduled for the remaining nodes that are in Ready state.

  4. If you want to uninstall all OpenShift Container Platform content from the node host, including all pods and containers, continue to Uninstalling Nodes and follow the procedure using the uninstall.yml playbook. The procedure assumes general understanding of the advanced installation method using Ansible.

Updating labels on nodes

To add or update labels on a node:

$ oc label node <node> <key_1>=<value_1> ... <key_n>=<value_n>

To see more detailed usage:

$ oc label -h

Listing pods on nodes

To list all or selected pods on one or more nodes:

$ oc adm manage-node <node1> <node2> \
    --list-pods [--pod-selector=<pod_selector>] [-o json|yaml]

To list all or selected pods on selected nodes:

$ oc adm manage-node --selector=<node_selector> \
    --list-pods [--pod-selector=<pod_selector>] [-o json|yaml]

Marking nodes as unschedulable or schedulable

By default, healthy nodes with a Ready status are marked as schedulable, meaning that new pods are allowed for placement on the node. Manually marking a node as unschedulable blocks any new pods from being scheduled on the node. Existing pods on the node are not affected.

To mark a node or nodes as unschedulable:

$ oc adm manage-node <node1> <node2> --schedulable=false

For example:

$ oc adm manage-node node1.example.com --schedulable=false
NAME                 LABELS                                        STATUS
node1.example.com    kubernetes.io/hostname=node1.example.com      Ready,SchedulingDisabled

To mark a currently unschedulable node or nodes as schedulable:

$ oc adm manage-node <node1> <node2> --schedulable

Alternatively, instead of specifying specific node names (e.g., <node1> <node2>), you can use the --selector=<node_selector> option to mark selected nodes as schedulable or unschedulable.

Evacuating pods on nodes

Evacuating pods allows you to migrate all or selected pods from a given node. Nodes must first be marked unschedulable to perform pod evacuation.

Only pods backed by a replication controller can be evacuated; the replication controllers create new pods on other nodes and remove the existing pods from the specified node(s). Bare pods, meaning those not backed by a replication controller, are unaffected by default. You can evacuate a subset of pods by specifying a pod-selector. Pod selector is based on labels, so all the pods with the specified label will be evacuated.

To evacuate all or selected pods on a node:

$ oc adm drain <node> [--pod-selector=<pod_selector>]

You can force deletion of bare pods by using the --force option. When set to true, deletion continues even if there are pods not managed by a replication controller, ReplicaSet, job, daemonset, or StatefulSet:

$ oc adm drain <node> --force=true

You can use --grace-period to set a period of time in seconds for each pod to terminate gracefully. If negative, the default value specified in the pod is used:

$ oc adm drain <node> --grace-period=-1

You can use --ignore-daemonsets and set it to true to ignore daemonset-managed pods:

$ oc adm drain <node> --ignore-daemonsets=true

You can use --timeout to set the length of time to wait before giving up. A value of 0 sets an infinite length of time:

$ oc adm drain <node> --timeout=5s

You can use --delete-local-data and set it to true to continue deletion even if there are pods using emptyDir (local data that is deleted when the node is drained):

$ oc adm drain <node> --delete-local-data=true

To list objects that will be migrated without actually performing the evacuation, use the --dry-run option and set it to true:

$ oc adm drain <node> --dry-run=true

Instead of specifying a specific node name, you can use the --selector=<node_selector> option to evacuate pods on nodes that match the selector.

Rebooting nodes

To reboot a node without causing an outage for applications running on the platform, it is important to first evacuate the pods. For pods that are made highly available by the routing tier, nothing else needs to be done. For other pods needing storage, typically databases, it is critical to ensure that they can remain in operation with one pod temporarily going offline. While implementing resiliency for stateful pods is different for each application, in all cases it is important to configure the scheduler to use node anti-affinity to ensure that the pods are properly spread across available nodes.

Another challenge is how to handle nodes that are running critical infrastructure such as the router or the registry. The same node evacuation process applies, though it is important to understand certain edge cases.

Infrastructure nodes

Infrastructure nodes are nodes that are labeled to run pieces of the OpenShift Container Platform environment. Currently, the easiest way to manage node reboots is to ensure that there are at least three nodes available to run infrastructure. The scenario below demonstrates a common mistake that can lead to service interruptions for the applications running on OpenShift Container Platform when only two nodes are available.

  • Node A is marked unschedulable and all pods are evacuated.

  • The registry pod running on that node is now redeployed on node B. This means node B is now running both registry pods.

  • Node B is now marked unschedulable and is evacuated.

  • The service exposing the two pod endpoints on node B, for a brief period of time, loses all endpoints until they are redeployed to node A.

The same process using three infrastructure nodes does not result in a service disruption. However, due to pod scheduling, the last node that is evacuated and brought back in to rotation is left running zero registries. The other two nodes will run two and one registries respectively. The best solution is to rely on pod anti-affinity. This is an alpha feature in Kubernetes that is available for testing now, but is not yet supported for production workloads.

Using pod anti-affinity

Pod anti-affinity is slightly different than node anti-affinity. Node anti-affinity can be violated if there are no other suitable locations to deploy a pod. Pod anti-affinity can be set to either required or preferred.

apiVersion: v1
kind: Pod
metadata:
  name: with-pod-antiaffinity
spec:
  affinity:
    podAntiAffinity: (1)
      preferredDuringSchedulingIgnoredDuringExecution: (2)
      - weight: 100 (3)
        podAffinityTerm:
          labelSelector:
            matchExpressions:
            - key: docker-registry (4)
              operator: In (5)
              values:
              - default
          topologyKey: kubernetes.io/hostname
1 Stanza to configure pod anti-affinity.
2 Defines a preferred rule.
3 Specifies a weight for a preferred rule. The node with the highest weight is preferred.
4 Description of the pod label that determines when the anti-affinity rule applies. Specify a key and value for the label.
5 The operator represents the relationship between the label on the existing pod and the set of values in the matchExpression parameters in the specification for the new pod. Can be In, NotIn, Exists, or DoesNotExist.

This example assumes the Docker registry pod has a label of docker-registry=default. Pod anti-affinity can use any Kubernetes match expression.

The last required step is to enable the MatchInterPodAffinity scheduler predicate in /etc/origin/master/scheduler.json. With this in place, if only two infrastructure nodes are available and one is rebooted, the Docker registry pod is prevented from running on the other node. oc get pods reports the pod as unready until a suitable node is available. Once a node is available and all pods are back in ready state, the next node can be restarted.

Handling nodes running routers

In most cases, a pod running an OpenShift Container Platform router will expose a host port. The PodFitsPorts scheduler predicate ensures that no router pods using the same port can run on the same node, and pod anti-affinity is achieved. If the routers are relying on IP failover for high availability, there is nothing else that is needed. For router pods relying on an external service such as AWS Elastic Load Balancing for high availability, it is that service’s responsibility to react to router pod restarts.

In rare cases, a router pod might not have a host port configured. In those cases, it is important to follow the recommended restart process for infrastructure nodes.

Configuring node resources

You can configure node resources by adding kubelet arguments to the node configuration file (/etc/origin/node/node-config.yaml). Add the kubeletArguments section and include any desired options:

kubeletArguments:
  max-pods: (1)
    - "40"
  resolv-conf: (2)
    - "/etc/resolv.conf"
  image-gc-high-threshold: (3)
    - "90"
  image-gc-low-threshold: (4)
    - "80"
  kube-api-qps: (5)
    - "20"
  kube-api-burst: (6)
    - "40"
1 Maximum number of pods that can run on this kubelet.
2 Resolver configuration file used as the basis for the container DNS resolution configuration.
3 The percent of disk usage after which image garbage collection is always run. Default: 90%
4 The percent of disk usage before which image garbage collection is never run. Lowest disk usage to garbage collect to. Default: 80%
5 The Queries per Second (QPS) to use while talking with the Kubernetes API server.
6 The burst to use while talking with the Kubernetes API server.

To view all available kubelet options:

$ hyperkube kubelet -h

This can also be set during an advanced installation using the openshift_node_kubelet_args variable. For example:

openshift_node_kubelet_args={'max-pods': ['40'], 'resolv-conf': ['/etc/resolv.conf'],  'image-gc-high-threshold': ['90'], 'image-gc-low-threshold': ['80']}

Setting maximum pods per node

See the Cluster Limits page for the maximum supported limits for each version of OpenShift Container Platform.

In the /etc/origin/node/node-config.yaml file, two parameters control the maximum number of pods that can be scheduled to a node: pods-per-core and max-pods. When both options are in use, the lower of the two limits the number of pods on a node. Exceeding these values can result in:

  • Increased CPU utilization on both OpenShift Container Platform and Docker.

  • Slow pod scheduling.

  • Potential out-of-memory scenarios (depends on the amount of memory in the node).

  • Exhausting the pool of IP addresses.

  • Resource overcommitting, leading to poor user application performance.

In Kubernetes, a pod that is holding a single container actually uses two containers. The second container is used to set up networking prior to the actual container starting. Therefore, a system running 10 pods will actually have 20 containers running.

pods-per-core sets the number of pods the node can run based on the number of processor cores on the node. For example, if pods-per-core is set to 10 on a node with 4 processor cores, the maximum number of pods allowed on the node will be 40.

kubeletArguments:
  pods-per-core:
    - "10"

Setting pods-per-core to 0 disables this limit.

max-pods sets the number of pods the node can run to a fixed value, regardless of the properties of the node. Cluster Limits documents maximum supported values for max-pods.

kubeletArguments:
  max-pods:
    - "250"

Using the above example, the default value for pods-per-core is 10 and the default value for max-pods is 250. This means that unless the node has 25 cores or more, by default, pods-per-core will be the limiting factor.

Resetting Docker storage

As you download Docker images and run and delete containers, Docker does not always free up mapped disk space. As a result, over time you can run out of space on a node, which might prevent OpenShift Container Platform from being able to create new pods or cause pod creation to take several minutes.

For example, the following shows pods that are still in the ContainerCreating state after six minutes and the events log shows a FailedSync event.

$ oc get pod
NAME                               READY     STATUS              RESTARTS   AGE
cakephp-mysql-persistent-1-build   0/1       ContainerCreating   0          6m
mysql-1-9767d                      0/1       ContainerCreating   0          2m
mysql-1-deploy                     0/1       ContainerCreating   0          6m

$ oc get events
LASTSEEN   FIRSTSEEN   COUNT     NAME                               KIND                    SUBOBJECT                     TYPE      REASON                         SOURCE                                                 MESSAGE
6m         6m          1         cakephp-mysql-persistent-1-build   Pod                                                   Normal    Scheduled                      default-scheduler                                      Successfully assigned cakephp-mysql-persistent-1-build to ip-172-31-71-195.us-east-2.compute.internal
2m         5m          4         cakephp-mysql-persistent-1-build   Pod                                                   Warning   FailedSync                     kubelet, ip-172-31-71-195.us-east-2.compute.internal   Error syncing pod
2m         4m          4         cakephp-mysql-persistent-1-build   Pod                                                   Normal    SandboxChanged                 kubelet, ip-172-31-71-195.us-east-2.compute.internal   Pod sandbox changed, it will be killed and re-created.

One solution to this problem is to reset Docker storage to remove artifacts not needed by Docker.

On the node where you want to restart Docker storage:

  1. Run the following command to mark the node as unschedulable:

    $ oc adm manage-node <node> --schedulable=false

  2. Run the following command to shut down Docker and the atomic-openshift-node service:

    $ systemctl stop docker atomic-openshift-node

  3. Run the following command to remove the local volume directory:

    $ rm -rf /var/lib/origin/openshift.local.volumes

    This command clears the local image cache. As a result, images, including ose-* images, will need to be re-pulled. This might result in slower pod start times while the image store recovers.

  4. Remove the /var/lib/docker directory:

    $ rm -rf /var/lib/docker

  5. Run the following command to reset the Docker storage:

    $ docker-storage-setup --reset

  6. Run the following command to recreate the Docker storage:

    $ docker-storage-setup

  7. Recreate the /var/lib/docker directory:

    $ mkdir /var/lib/docker

  8. Run the following command to restart Docker and the atomic-openshift-node service:

    $ systemctl start docker atomic-openshift-node

  9. Run the following command to mark the node as schedulable:

    $ oc adm manage-node <node> --schedulable=true

Changing node traffic interface

By default, DNS routes all node traffic. During node registration, the master receives the node IP addresses from the DNS configuration, and therefore accessing nodes via DNS is the most flexible solution for most deployments.

If your deployment is using a cloud provider, then the node gets the IP information from the cloud provider. However, openshift-sdn attempts to determine the IP through a variety of methods, including a DNS lookup on the nodeName (if set), or on the system hostname (if nodeName is not set).

However, you may need to change the node traffic interface. For example, where:

  • OpenShift Container Platform is installed in a cloud provider where internal hostnames are not configured/resolvable by all hosts.

  • The node’s IP from the master’s perspective is not the same as the node’s IP from its own perspective.

Configuring the openshift_set_node_ip Ansible variable forces node traffic through an interface other than the default network interface.

To change the node traffic interface:

  1. Set the openshift_set_node_ip Ansible variable to true.

  2. Set the openshift_ip to the IP address for the node you want to configure.

Although openshift_set_node_ip can be useful as a workaround for the cases stated in this section, it is generally not suited for production environments. This is because the node will no longer function properly if it receives a new IP address.