如何在 K8S 的 Pod 内连续执行 Container？这种方法别错过
出于某些目的，有时需要在 Kubernetes 的一个 Pod 中，连续依次运行多个 Container。这种有明确结束预期的运行，即 Kubernetes 的 Job。但是，虽然一个 Job 可以在一个 Pod 内运行多个 Container，然而运行方式是并发的。
Kubernetes Job
经过调查发现，虽然 containers 不能依次运行，但是 initContainers 可以。它是在containers 运行前，执行的初始化操作，依次结束运行并且无异常后，正式的containers 才会运行。利用这一点，可以实现多个任务的依次执行，把前面的任务写到initContainers、后一个任务写到 containers 即可。
以下为三个 Containter 依次执行的样例。
apiVersion: batch/v1kind: Jobmetadata: name: sequential-jobsspec: backoffLimit: ttlSecondsAfterFinished: 3600 template: spec: activeDeadlinesSeconds: 60 restartPolicy: Never initContainers: - name: job-1 image: alpine:3.11 command: - 'sh' - '-c' - > for i in 1 2 3; do echo "job-1 `date`"; sleep 1s; done; echo code > /srv/input/code volumeMounts: - mountPath: /srv/input/ name: input - name: job-2 image: alpine:3.11 command: - 'sh' - '-c' - > for i in 1 2 3; do echo "job-2 `date`"; sleep 1s; done; cat /srv/input/code && echo artifact > /srv/input/output/artifact resources: requests: cpu: 3 volumeMounts: - mountPath: /srv/input/ name: input - mountPath: /srv/input/output/ name: output containers: - name: job-3 image: alpine:3.11 command: - 'sh' - '-c' - > echo "job-1 and job-2 completed"; sleep 3s; cat /srv/output/artifact volumeMounts: - mountPath: /srv/output/ name: output volumes: - name: input emptyDir: {} - name: output emptyDir: {} securityContext: runAsUser: 2000 runAsGroup: 2000 fsGroup: 2000
backoffLimit: 0，这句指定这个Job不要失败重启。
volumes 这部分，使用了 input 和 output 两个 emptyDir，作为输入输出。
securityContext 可以在镜像默认用户不确定的情况下，使用指定UID进行Volume操作，避免对 root 的依赖。
-
activeDeadlinesSeconds 指定了 Job 内 Pod 的超时时间。
这个字段同样可以给到Job。
ttlSecondsAfterFinished 指定了在多久以后，Job会被自动删除。
运行完毕后，日志如下：
$ kubectl logs sequential-jobs-r4725 job-1job-1 Tue Jul 28 07:50:10 UTC 2020job-1 Tue Jul 28 07:50:11 UTC 2020job-1 Tue Jul 28 07:50:12 UTC 2020$ kubectl logs sequential-jobs-r4725 job-2job-2 Tue Jul 28 07:50:13 UTC 2020job-2 Tue Jul 28 07:50:14 UTC 2020job-2 Tue Jul 28 07:50:15 UTC 2020code$ kubectl logs sequential-jobs-r4725 job-3job-1 and job-2 completedartifact
Volcano
stateDiagram [*] → Pending Pending → Aborted Pending → Running Aborted → Pending Running → Aborted Running → Completed Running → Terminated Completed → [*] Terminated → [*]
apiVersion: batch.volcano.sh/v1alpha1kind: Jobmetadata: name: volcano-sequential-jobsspec: minAvailable: 1 schedulerName: volcano queue: default tasks: - replicas: 1 name: "task-1" template: spec: restartPolicy: Never initContainers: - name: job-1 image: alpine:3.11 command: - 'sh' - '-c' - > for i in 1 2 3; do echo "job-1 `date`"; sleep 1s; done; echo code > /srv/input/code volumeMounts: - mountPath: /srv/input/ name: input - name: job-2 image: alpine:3.11 command: - 'sh' - '-c' - > for i in 1 2 3; do echo "job-2 `date`"; sleep 1s; done; cat /srv/input/code && echo artifact > /srv/input/output/artifact resources: requests: cpu: 3 volumeMounts: - mountPath: /srv/input/ name: input - mountPath: /srv/input/output/ name: output containers: - name: job-done image: alpine:3.11 command: - 'sh' - '-c' - > echo "job-1 and job-2 completed"; sleep 3s; cat /srv/output/artifact volumeMounts: - mountPath: /srv/output/ name: output volumes: - name: input emptyDir: {} - name: output emptyDir: {} securityContext: runAsUser: 2000 runAsGroup: 2000 fsGroup: 2000
上面与原生相比，虽然多了 tasks 这一层概念，但是在功能上并无帮助。
运行完毕后，日志如下：
$ kubectl logs volcano-sequential-jobs-task-1- job-1job-1 Tue Jul 28 07:53:17 UTC 2020job-1 Tue Jul 28 07:53:18 UTC 2020job-1 Tue Jul 28 07:53:20 UTC 2020$ kubectl logs volcano-sequential-jobs-task-1- job-2job-2 Tue Jul 28 07:53:21 UTC 2020job-2 Tue Jul 28 07:53:22 UTC 2020job-2 Tue Jul 28 07:53:23 UTC 2020code$ kubectl logs volcano-sequential-jobs-task-1- job-3job-1 and job-2 completedartifact
argo
总结
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