Oracle Cloud Infrastructure Documentation

Using Preemptible Capacity to Provision Worker Nodes

Find out how to specify preemptible capacity for compute instances hosting worker nodes in the node pools of clusters you've created using Container Engine for Kubernetes (OKE).

When using Container Engine for Kubernetes to define a node pool's placement configuration, you can specify preemptible capacity as the capacity type for compute instances hosting worker nodes in the node pool. Specifying preemptible capacity allows you to save money by using preemptible instances to run workloads that only need to run for brief periods or that can be interrupted when the capacity is reclaimed.

Preemptible instances behave the same as regular compute instances, but the capacity is reclaimed when it's needed elsewhere, and the instances are terminated. If workloads are fault-tolerant and can withstand interruptions, then preemptible instances can reduce costs. For example, you can use preemptible instances to optimize costs for workloads that can tolerate interruptions, such as tests that can be stopped and resumed later. For more information, see Preemptible Instances.

When a preemptible instance hosting a worker node is to be terminated, Container Engine for Kubernetes is notified. Before the node instance is terminated, Container Engine for Kubernetes:

  • cordons the worker node to prevent the kube-scheduler from placing new pods onto that node
  • drains the worker node to safely evict pods, ensuring the pod's containers terminate gracefully and perform any necessary cleanup

After a preemptible instance hosting a worker node has been terminated, Container Engine for Kubernetes attempts to create a new preemptible instance as a replacement. If Container Engine for Kubernetes is unable to create a replacement preemptible instance after multiple attempts, a message is output.

When you choose preemptible capacity as the capacity type for a node pool:

  • Container Engine for Kubernetes automatically adds a Kubernetes label oci.oraclecloud.com/oke-is-preemptible=true to the worker nodes hosted on preemptible instances. You can use the label with Kubernetes node selectors and node affinity/anti-affinity to control which pods are scheduled on those worker nodes. See Assigning Pods to Nodes in the Kubernetes documentation.
  • Container Engine for Kubernetes automatically adds a Kubernetes taint oci.oraclecloud.com/oke-is-preemptible to the worker nodes hosted on preemptible instances. You can use the taint with Kubernetes tolerations to control which pods are scheduled on those worker nodes. See Taints and Tolerations in the Kubernetes documentation.
  • You can specify whether the boot volumes attached to the preemptible instances hosting worker nodes are permanently deleted if the instances are terminated.

Note the following:

  • Many, but not all, compute shapes support preemptible instances. In particular, note that preemptible instances are not supported by bare metal shapes. You cannot create a node pool with a capacity type of preemptible capacity if the node pool's shape does not support preemptible instances. Similarly, you cannot change a node pool's capacity type to preemptible capacity if the node pool's shape does not support preemptible instances.
  • Preemptible instances have a number of limitations and restrictions. See Support and Limitations.
  • Any changes you make to worker node properties only apply to new worker nodes. Updating the capacity type associated with a node pool does not impact the properties of existing worker nodes.

Best Practices When Using Preemptible Capacity

When you choose preemptible capacity as the capacity type for a node pool, consider the following best practices:

  • Preemptible instances are best suited for fault tolerant containerized workloads. When designing applications that might run on preemptible instances, assume that the preemptible capacity could be reclaimed (and the preemptible instances terminated) at any time.
  • Use Kubernetes node selectors and node affinity/anti-affinity, along with Kubernetes taints and tolerations, to ensure that only fault tolerant workloads are scheduled to run on preemptible instances. See Assigning Pods to Nodes in the Kubernetes documentation.
  • Oracle recommends you do not specify preemptible capacity as the capacity type for the primary node pool in a cluster. Instead, only specify preemptible capacity for additional node pools that supplement the cluster's primary node pool.
  • Oracle recommends you avoid the situation where a node pool has a mix of capacity types. Although a mix of capacity types in the same node pool is supported, Oracle recommends all worker nodes in the node pool have the same capacity type to make node pool management easier. For example, Oracle recommends you:
    • avoid specifying on-demand capacity in one availability domain and preemptible capacity in a second availability domain
    • avoid changing the capacity type from on-demand capacity to preemptible capacity when scaling up a node pool to add more nodes

Using the Console

Creating A Cluster and Specifying Preemptible Capacity

  1. Follow the instructions to create a cluster using the 'Custom Create' workflow. See Using the Console to create a Cluster with Explicitly Defined Settings in the 'Custom Create' workflow.
  2. When specifying the Placement Configuration for a node pool in the cluster:
    1. Specify the first availability domain and subnet:
      • Availability Domain: Select the availability domain in which to place worker nodes.
      • Fault Domain: (Optional) One or more fault domains in the availability domain in which to place worker nodes.
      • Subnet: Select the subnet configured to host worker nodes.

    2. Click Show Advanced Options and specify that you want to use preemptible instances to provision worker nodes in the node pool:

      • Capacity Type: Select Preemptible Capacity.
      • When reclaimed, permanently delete the attached boot volume: Choose whether to permanently delete the attached boot volume when the capacity is reclaimed.
    3. Optionally click Another Row to add additional availability domains, subnets, and capacity types to the placement configuration. If you specify multiple availability domains in a node pool's placement configuration, you can specify a different capacity type for each availability domain. However, Oracle recommends all worker nodes in the node pool have the same capacity type to make node pool management easier.

Creating A Node Pool and Specifying Preemptible Capacity

  1. Open the navigation menu and click Developer Services. Under Containers & Artifacts, click Kubernetes Clusters (OKE).
  2. Choose a Compartment you have permission to work in.
  3. On the Cluster List page, click the name of the cluster where you want to create a new node pool.
  4. On the Cluster page, display the Node Pools tab, and then click Add Node Pool to create a new node pool and specify the required properties for its worker nodes.
  5. When specifying the Placement Configuration for a node pool in the cluster:
    1. Specify the first availability domain and subnet:
      • Availability Domain: Select the availability domain in which to place worker nodes.
      • Fault Domain: (Optional) One or more fault domains in the availability domain in which to place worker nodes.
      • Subnet: Select the subnet configured to host worker nodes.

    2. Click Show Advanced Options and specify that you want to use preemptible instances to provision worker nodes in the node pool:

      • Capacity Type: Select Preemptible Capacity.
      • When reclaimed, permanently delete the attached boot volume: Choose whether to permanently delete the attached boot volume when the capacity is reclaimed.
    3. Optionally click Another Row to add additional availability domains, subnets, and capacity types to the placement configuration. If you specify multiple availability domains in a node pool's placement configuration, you can specify a different capacity type for each availability domain. However, Oracle recommends all worker nodes in the node pool have the same capacity type to make node pool management easier.

Updating A Node Pool and Specifying Preemptible Capacity

  1. Open the navigation menu and click Developer Services. Under Containers & Artifacts, click Kubernetes Clusters (OKE).
  2. Choose a Compartment you have permission to work in.
  3. On the Cluster List page, click the name of the cluster you want to modify.
  4. Click Node Pools under Resources, and click the name of the node pool you want to modify.
  5. On the Node Pool Details page, click Edit.
  6. When specifying the Placement Configuration for a node pool in the cluster:
    1. Specify the first availability domain and subnet:
      • Availability Domain: Select the availability domain in which to place worker nodes.
      • Fault Domain: (Optional) One or more fault domains in the availability domain in which to place worker nodes.
      • Subnet: Select the subnet configured to host worker nodes.

    2. Click Show Advanced Options and specify that you want to use preemptible instances to provision worker nodes in the node pool:

      • Capacity Type: Select Preemptible Capacity.
      • When reclaimed, permanently delete the attached boot volume: Choose whether to permanently delete the attached boot volume when the capacity is reclaimed.
    3. Optionally click Another Row to add additional availability domains, subnets, and capacity types to the placement configuration. If you specify multiple availability domains in a node pool's placement configuration, you can specify a different capacity type for each availability domain. However, Oracle recommends all worker nodes in the node pool have the same capacity type to make node pool management easier.
  7. Save the changes.

Using the CLI

For information about using the CLI, see Command Line Interface (CLI). For a complete list of flags and options available for CLI commands, see the Command Line Reference.

Creating A Node Pool and Specifying Preemptible Capacity

To use the CLI to create a node pool that uses preemptible capacity to provision worker nodes, include the preemptibleNodeConfig argument in the --placement-configs parameter.

For example: 

oci ce node-pool create \
--cluster-id ocid1.cluster.oc1.iad.aaaaaaaaaf______jrd \
--name test-node \
--node-image-id ocid1.image.oc1.iad.aaaaaaaa6______nha \
--compartment-id oocid1.compartment.oc1..aaaaaaaay______t6q \
--kubernetes-version v1.21.5 \
--node-shape VM.Standard2.1 \
--placement-configs "[{\"availability-domain\":\"IqDk:US-ASHBURN-AD-2\", \"preemptibleNodeConfig\": {\"preemptionAction\":{\"isPreserveBootVolume\":false, \"type\":\"TERMINATE\"}}, \"subnet-id\":\"ocid1.subnet.oc1.iad.aaaaaaaa2xpk______zva\", \"faultDomains\":[\"FAULT-DOMAIN-3\", \"FAULT-DOMAIN-1\"]}, {\"availability-domain\":\"IqDk:US-ASHBURN-AD-1\", \"preemptibleNodeConfig\": {\"preemptionAction\":{\"isPreserveBootVolume\":false, \"type\":\"TERMINATE\"}}, \"subnet-id\":\"ocid1.subnet.oc1.iad.aaaaaaaauhls______bpq\", \"faultDomains\": [\"FAULT-DOMAIN-1\", \"FAULT-DOMAIN-2\"]}]" \
--size 1 \
--region=us-ashburn-1 \

If you specify multiple availability domains in a node pool's placement configuration, you can specify a different capacity type for each availability domain. However, Oracle recommends all worker nodes in the node pool have the same capacity type to make node pool management easier.

Using the API

For information about using the API and signing requests, see REST API documentation and Security Credentials. For information about SDKs, see SDKs and the CLI.

Use the placementConfigs attribute of the nodeConfigDetails object to specify capacity type when creating or updating node pools.

If you specify multiple availability domains in a node pool's placement configuration, you can specify a different capacity type for each availability domain. However, Oracle recommends all worker nodes in the node pool have the same capacity type to make node pool management easier.