Run jobs on a preemptible elastic container instance - Elastic Container Instance

Preemptible instances run at the real-time spot price, which can significantly reduce compute costs for fault-tolerant, short-lived workloads such as batch jobs, CI/CD pipelines, and stateless web services. This topic describes how to run a Kubernetes Job on a preemptible Elastic Container Instance (ECI)-based pod.

How preemptible instances work

Billing

The spot price fluctuates based on supply and demand for the instance type. When you create a preemptible instance, you specify a bid strategy. If your bid price is higher than the real-time spot price and resources are available, the instance is created. The instance then enters a protection period, during which it is billed at the spot price at the time of purchase. The protection period lasts 1 hour by default. After the protection period expires, billing switches to the real-time spot price.
Reclaim mechanism

After the protection period expires, ECI checks the spot price and resource inventory every 5 minutes. If the real-time spot price exceeds your bid price or resources are insufficient, the instance is released. ECI sends a SpotToBeReleased event to the Kubernetes event list approximately 5 minutes before release. Use this window to gracefully handle the interruption — for example, you can configure to deny inbound traffic to the instance.
Creation methods

You can create a preemptible instance by specifying ECS instance types or by specifying the number of vCPUs and the memory size.
Bid strategies

Add the k8s.aliyun.com/eci-spot-strategy annotation to the pod metadata to set the bid strategy.

Valid values:
- SpotAsPriceGo: ECI automatically uses the real-time spot price as your bid.
- SpotWithPriceLimit: You set the maximum hourly price you are willing to pay. Also add the k8s.aliyun.com/eci-spot-price-limit annotation to specify the maximum hourly price.

For more information, see Create a spot instance.

Run a job on a preemptible instance

Kubernetes Jobs batch-process short-lived, one-off tasks. The following steps show how to run a Job on a preemptible instance.

To improve instance creation success rate, specify multiple instance types in the k8s.aliyun.com/eci-use-specs annotation.

Create the Job configuration file and save it as spot_job.yaml.

apiVersion: batch/v1
kind: Job
metadata:
  name: pi
spec:
  template:
    metadata:
      annotations:
        k8s.aliyun.com/eci-use-specs: ecs.c5.large,2-4Gi # Specifies multiple instance specifications to improve the success rate of instance creation.
        k8s.aliyun.com/eci-spot-strategy: SpotAsPriceGo    # The current market price is automatically used as the bid price.
    spec:
      containers:
      - name: pi
        image: registry-vpc.cn-beijing.aliyuncs.com/ostest/perl
        command: ["perl",  "-Mbignum=bpi", "-wle", "print bpi(2000)"]
      restartPolicy: Never

Create the Job.
```
kubectl create -f spot_job.yaml
```
Check the pod status.
```
kubectl get pod
```
- If the Job is running, the pod status is Running.
```
NAME       READY   STATUS      RESTARTS   AGE
pi-frmr8   1/1     Running     0          35s
```
- If the Job completes successfully, the pod status changes to Completed.
```
NAME       READY   STATUS      RESTARTS   AGE
pi-frmr8   0/1     Completed   0          2h
```
- If the instance is reclaimed before the Job finishes, the pod status changes to BidFailed and the Job controller automatically creates a new pod to continue the Job.
  
  The original pod is retained in BidFailed state.
  
  Note
  After a preemptible instance is created, it runs as expected during the protection period. After the protection period expires, the instance is released if the real-time spot price exceeds your bid price or resources are insufficient. A pre-release event (SpotToBeReleased) is generated approximately 5 minutes before release. For more information, see Reclamation details.
```
NAME       READY   STATUS      RESTARTS   AGE
pi-frmr8   1/1     BidFailed   0          4h53m
pi-kp5zx   1/1     Running     0          3h45m
```