Chapter 2. Managing Nodes
2.1. 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.
2.2. Listing Nodes
To list all nodes that are known to the master:
$ oc get nodes NAME STATUS AGE master.example.com Ready,SchedulingDisabled 165d node1.example.com Ready 165d node2.example.com Ready 165d
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:
| Condition | Description |
|---|---|
|
|
The node is passing the health checks performed from the master by returning |
|
| The node is not passing the health checks performed from the master. |
|
| 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 Role: 2 Labels: beta.kubernetes.io/arch=amd64 3 beta.kubernetes.io/os=linux kubernetes.io/hostname=node1.example.com region=infra zone=default Taints: <none> CreationTimestamp: Sun, 11 Mar 2018 08:06:02 -0400 Phase: Conditions: 4 Type Status LastHeartbeatTime LastTransitionTime Reason Message ---- ------ ----------------- ------------------ ------ ------- OutOfDisk False Wed, 30 May 2018 06:36:40 -0400 Sun, 11 Mar 2018 08:06:02 -0400 KubeletHasSufficientDisk kubelet has sufficient disk space available MemoryPressure False Wed, 30 May 2018 06:36:40 -0400 Sun, 11 Mar 2018 08:06:02 -0400 KubeletHasSufficientMemory kubelet has sufficient memory available DiskPressure False Wed, 30 May 2018 06:36:40 -0400 Sun, 11 Mar 2018 08:06:02 -0400 KubeletHasNoDiskPressure kubelet has no disk pressure Ready True Wed, 30 May 2018 06:36:40 -0400 Fri, 23 Mar 2018 08:43:27 -0400 KubeletReady kubelet is posting ready status Addresses: 10.74.158.197,10.74.158.197,infra-0.rktest.quicklab.pnq2.cee.redhat.com 5 Capacity: 6 alpha.kubernetes.io/nvidia-gpu: 0 cpu: 1 memory: 8010568Ki pods: 10 Allocatable: alpha.kubernetes.io/nvidia-gpu: 0 cpu: 1 memory: 8010568Ki pods: 10 System Info: 7 Machine ID: 81c4f1f14c5db09b1e8d87a System UUID: 81C4F1F1-A4A-86C5-DB09B1E8D87A Boot ID: 475eb2fd-0a3-b79b-6a1fa45da5e6 Kernel Version: 3.10.0-693.el7.x86_64 OS Image: Employee SKU Operating System: linux Architecture: amd64 Container Runtime Version: docker://1.10.3 Kubelet Version: v1.5.2+43a9be4 Kube-Proxy Version: v1.5.2+43a9be4 ExternalID: node1.example.com 8 Non-terminated Pods: (4 in total) 9 Namespace Name CPU Requests CPU Limits Memory Requests Memory Limits --------- ---- ------------ ---------- --------------- ------------- default docker-registry-3-0crt1 100m (10%) 0 (0%) 256Mi (3%) 0 (0%) default router-1-qp0zg 100m (10%) 0 (0%) 256Mi (3%) 0 (0%) farm mysql 500m (50%) 500m (50%) 0 (0%) 0 (0%) mysql mysql-3-2ms9s 0 (0%) 0 (0%) 0 (0%) 0 (0%) Allocated resources: (Total limits may be over 100 percent, i.e., overcommitted. CPU Requests CPU Limits Memory Requests Memory Limits ------------ ---------- --------------- ------------- 700m (70%) 500m (50%) 512Mi (6%) 0 (0%) No events.
2.3. 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.
2.4. 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:
- Evacuate pods from the node you are preparing to delete.
Delete the node object:
$ oc delete node <node>
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.
- 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.
2.5. 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
2.6. 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]2.7. 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.
2.8. Evacuating Pods on Nodes
Evacuating pods allows you to migrate all or selected pods from a given node or nodes. 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 one or more nodes:
$ oc adm drain <node1> <node2>
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 <node1> <node2> --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 will be used:
$ oc adm drain <node1> <node2> --grace-period=-1
You can use --ignore-daemonsets and set it to true to ignore daemonset-managed pods:
$ oc adm drain <node1> <node2> --ignore-daemonset=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 <node1> <node2> --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 will be deleted when the node is drained):
$ oc adm drain <node1> <node2> --delete-local-data=true
2.9. 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.
2.9.1. 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.
2.9.2. Using Pod Anti-Affinity for the Docker Registry Pod
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.
Using the docker-registry pod as an example, the first step in enabling this feature is to set the scheduler.alpha.kubernetes.io/affinity on the pod. Since this pod uses a deployment configuration, the most appropriate place to add the annotation is to the pod template’s metadata.
$ oc edit dc/docker-registry -o yaml
...
template:
metadata:
annotations:
scheduler.alpha.kubernetes.io/affinity: |
{
"podAntiAffinity": {
"requiredDuringSchedulingIgnoredDuringExecution": [{
"labelSelector": {
"matchExpressions": [{
"key": "docker-registry",
"operator": "In",
"values":["default"]
}]
},
"topologyKey": "kubernetes.io/hostname"
}]
}
}
scheduler.alpha.kubernetes.io/affinity is internally stored as a string even though the contents are JSON. The above example shows how this string can be added as an annotation to a YAML deployment configuration.
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.
2.9.3. 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.
2.10. 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"
- 1
- 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%
To view all available kubelet options:
$ 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']}2.10.1. Setting Maximum Pods Per Node
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.
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.
2.11. 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:
Run the following command to mark the node as unschedulable:
$ oc adm manage-node <node> --schedulable=false
Run the following command to shut down Docker and the atomic-openshift-node service:
$ systemctl stop docker atomic-openshift-node
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.Remove the /var/lib/docker directory:
$ rm -rf /var/lib/docker
Run the following command to reset the Docker storage:
$ docker-storage-setup --reset
Run the following command to recreate the Docker storage:
$ docker-storage-setup
Recreate the /var/lib/docker directory:
$ mkdir /var/lib/docker
Run the following command to restart Docker and the atomic-openshift-node service:
$ systemctl start docker atomic-openshift-node
Run the following command to mark the node as schedulable:
$ oc adm manage-node <node> --schedulable=true
2.12. 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:
-
Set the
openshift_set_node_ipAnsible variable totrue. -
Set the
openshift_ipto 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.
