ArgoWorkflow教程(七)---高效的步骤间文件共享策略

之前我们分析了使用 artifact 实现步骤间文件共享，今天分享一下如何使用 PVC 实现高效的步骤间文件共享。

1. 概述

之前在 artifact 篇我们演示了如何使用 artifact 实现步骤间文件传递，今天介绍一种更为简单的文件传递方式：PVC 共享。

artifact 毕竟是借助 S3 实现中转，效率上肯定是低于直接共享 PVC 的，而且 artifact 一般用于结果输出，将最终结果保存到 S3，而不是单纯的用来共享文件。

2. 使用 artifact 共享文件

之前已经分享过了怎么通过 artifact 在不同步骤之间传递文件，这里在回顾一下。

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: artifact-passing-
spec:
  entrypoint: artifact-example
  templates:
  - name: artifact-example
    steps:
    - - name: generate-artifact
        template: whalesay
    - - name: consume-artifact
        template: print-message
        arguments:
          artifacts:
          # bind message to the hello-art artifact
          # generated by the generate-artifact step
          - name: message
            from: "{{steps.generate-artifact.outputs.artifacts.hello-art}}"

  - name: whalesay
    container:
      image: docker/whalesay:latest
      command: [sh, -c]
      args: ["cowsay hello world | tee /tmp/hello_world.txt"]
    outputs:
      artifacts:
      # generate hello-art artifact from /tmp/hello_world.txt
      # artifacts can be directories as well as files
      - name: hello-art
        path: /tmp/hello_world.txt

  - name: print-message
    inputs:
      artifacts:
      # unpack the message input artifact
      # and put it at /tmp/message
      - name: message
        path: /tmp/message
    container:
      image: alpine:latest
      command: [sh, -c]
      args: ["cat /tmp/message"]

可以看到，artifact 方式共享文件步骤间传递参数是比较类似。

导出 artifact

outputs:
  artifacts:
  # generate hello-art artifact from /tmp/hello_world.txt
  # artifacts can be directories as well as files
  - name: hello-art
    path: /tmp/hello_world.txt

后续步骤引用导出的 artifact

arguments:
  artifacts:
  # bind message to the hello-art artifact
  # generated by the generate-artifact step
  - name: message
    from: "{{steps.generate-artifact.outputs.artifacts.hello-art}}"

以及步骤中怎么将 artifact 引入，比如下面 demo 则是将 artifact 做为 /tmp/message 挂载到 Pod 中。

inputs:
  artifacts:
  # unpack the message input artifact
  # and put it at /tmp/message
  - name: message
    path: /tmp/message

3. 使用 PVC 高效共享文件

顾名思义，就是不同步骤都挂载同一个 PVC，这样自然就实现了文件共享。

ArgoWorkflow 中的每一步都会单独启动一个 Pod 来运行

也有两种方式：

• 1）动态创建 PVC：Workflow 运行时创建 PVC，运行结束后删除 PVC
• 2）使用已有 PVC：不会创建也不会删除

动态创建 PVC

完整 Demo 如下：

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: volumes-pvc-
spec:
  entrypoint: volumes-pvc-example
  volumeClaimTemplates:                 # define volume, same syntax as k8s Pod spec
  - metadata:
      name: workdir                     # name of volume claim
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi                  # Gi => 1024 * 1024 * 1024

  templates:
  - name: volumes-pvc-example
    steps:
    - - name: generate
        template: whalesay
    - - name: print
        template: print-message

  - name: whalesay
    container:
      image: docker/whalesay:latest
      command: [sh, -c]
      args: ["echo generating message in volume; cowsay hello world | tee /mnt/vol/hello_world.txt"]
      # Mount workdir volume at /mnt/vol before invoking docker/whalesay
      volumeMounts:                     # same syntax as k8s Pod spec
      - name: workdir
        mountPath: /mnt/vol

  - name: print-message
    container:
      image: alpine:latest
      command: [sh, -c]
      args: ["echo getting message from volume; find /mnt/vol; cat /mnt/vol/hello_world.txt"]
      # Mount workdir volume at /mnt/vol before invoking docker/whalesay
      volumeMounts:                     # same syntax as k8s Pod spec
      - name: workdir
        mountPath: /mnt/vol

首先定义了一个 PVC 模版，Workflow 运行时就会使用该模版创建一个 PVC

spec:
  entrypoint: volumes-pvc-example
  volumeClaimTemplates:                 # define volume, same syntax as k8s Pod spec
  - metadata:
      name: workdir                     # name of volume claim
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 1Gi                  # Gi => 1024 * 1024 * 1024

然后其他步骤需要将该 PVC 挂载到对应目录

  - name: whalesay
    container:
      image: docker/whalesay:latest
      command: [sh, -c]
      args: ["echo generating message in volume; cowsay hello world | tee /mnt/vol/hello_world.txt"]
      # Mount workdir volume at /mnt/vol before invoking docker/whalesay
      volumeMounts:                     # same syntax as k8s Pod spec
      - name: workdir
        mountPath: /mnt/vol

  - name: print-message
    container:
      image: alpine:latest
      command: [sh, -c]
      args: ["echo getting message from volume; find /mnt/vol; cat /mnt/vol/hello_world.txt"]
      # Mount workdir volume at /mnt/vol before invoking docker/whalesay
      volumeMounts:                     # same syntax as k8s Pod spec
      - name: workdir
        mountPath: /mnt/vol

这样就实现了文件共享，非常简单。

等 Workflow 运行结束后，Argo 会自动将创建出的 PVC 删除。

使用已有 PVC

在某些情况下，我们可以希望访问已经存在的卷，而不是动态创建/销毁卷。

完整 Demo 如下：

# Define Kubernetes PVC
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: my-existing-volume
spec:
  accessModes: [ "ReadWriteOnce" ]
  resources:
    requests:
      storage: 1Gi

---
apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: volumes-existing-
spec:
  entrypoint: volumes-existing-example
  volumes:
  # Pass my-existing-volume as an argument to the volumes-existing-example template
  # Same syntax as k8s Pod spec
  - name: workdir
    persistentVolumeClaim:
      claimName: my-existing-volume

  templates:
  - name: volumes-existing-example
    steps:
    - - name: generate
        template: whalesay
    - - name: print
        template: print-message

  - name: whalesay
    container:
      image: docker/whalesay:latest
      command: [sh, -c]
      args: ["echo generating message in volume; cowsay hello world | tee /mnt/vol/hello_world.txt"]
      volumeMounts:
      - name: workdir
        mountPath: /mnt/vol

  - name: print-message
    container:
      image: alpine:latest
      command: [sh, -c]
      args: ["echo getting message from volume; find /mnt/vol; cat /mnt/vol/hello_world.txt"]
      volumeMounts:
      - name: workdir
        mountPath: /mnt/vol

首先就是手动创建一个 PVC

# Define Kubernetes PVC
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: my-existing-volume
spec:
  accessModes: [ "ReadWriteOnce" ]
  resources:
    requests:
      storage: 1Gi

然后在 Workflow 中定义要使用这个 PVC

apiVersion: argoproj.io/v1alpha1
kind: Workflow
metadata:
  generateName: volumes-existing-
spec:
  entrypoint: volumes-existing-example
  volumes:
  # Pass my-existing-volume as an argument to the volumes-existing-example template
  # Same syntax as k8s Pod spec
  - name: workdir
    persistentVolumeClaim:
      claimName: my-existing-volume

可以看做是使用 persistentVolumeClaim 来替换了之前的 volumeClaimTemplates

然后就是步骤将这个 PVC 挂载到对应目录

  - name: whalesay
    container:
      image: docker/whalesay:latest
      command: [sh, -c]
      args: ["echo generating message in volume; cowsay hello world | tee /mnt/vol/hello_world.txt"]
      volumeMounts:
      - name: workdir
        mountPath: /mnt/vol

  - name: print-message
    container:
      image: alpine:latest
      command: [sh, -c]
      args: ["echo getting message from volume; find /mnt/vol; cat /mnt/vol/hello_world.txt"]
      volumeMounts:
      - name: workdir
        mountPath: /mnt/vol

这一步和使用动态创建 PVC 时没有任何变化。

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4. 小结

本文主要分析了 Argo 中的 Workflow 中怎么使用 PVC 共享文件。

• 1）定义 PVC 模版或者指定使用已有的 PVC
• 2）步骤中将 PVC 挂载到对应目录使用