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-exampletemplates:- name: artifact-examplesteps:- - name: generate-artifacttemplate: whalesay- - name: consume-artifacttemplate: print-messagearguments:artifacts:# bind message to the hello-art artifact# generated by the generate-artifact step- name: messagefrom: "{{steps.generate-artifact.outputs.artifacts.hello-art}}"- name: whalesaycontainer:image: docker/whalesay:latestcommand: [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-artpath: /tmp/hello_world.txt- name: print-messageinputs:artifacts:# unpack the message input artifact# and put it at /tmp/message- name: messagepath: /tmp/messagecontainer:image: alpine:latestcommand: [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-artpath: /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: messagefrom: "{{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: messagepath: /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-examplevolumeClaimTemplates: # define volume, same syntax as k8s Pod spec- metadata:name: workdir # name of volume claimspec:accessModes: [ "ReadWriteOnce" ]resources:requests:storage: 1Gi # Gi => 1024 * 1024 * 1024templates:- name: volumes-pvc-examplesteps:- - name: generatetemplate: whalesay- - name: printtemplate: print-message- name: whalesaycontainer:image: docker/whalesay:latestcommand: [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/whalesayvolumeMounts: # same syntax as k8s Pod spec- name: workdirmountPath: /mnt/vol- name: print-messagecontainer:image: alpine:latestcommand: [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/whalesayvolumeMounts: # same syntax as k8s Pod spec- name: workdirmountPath: /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-examplevolumeClaimTemplates: # define volume, same syntax as k8s Pod spec- metadata:name: workdir # name of volume claimspec: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: whalesaycontainer:image: docker/whalesay:latestcommand: [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/whalesayvolumeMounts: # same syntax as k8s Pod spec- name: workdirmountPath: /mnt/vol- name: print-messagecontainer:image: alpine:latestcommand: [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/whalesayvolumeMounts: # same syntax as k8s Pod spec- name: workdirmountPath: /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-examplevolumes:# Pass my-existing-volume as an argument to the volumes-existing-example template# Same syntax as k8s Pod spec- name: workdirpersistentVolumeClaim:claimName: my-existing-volumetemplates:- name: volumes-existing-examplesteps:- - name: generatetemplate: whalesay- - name: printtemplate: print-message- name: whalesaycontainer:image: docker/whalesay:latestcommand: [sh, -c]args: ["echo generating message in volume; cowsay hello world | tee /mnt/vol/hello_world.txt"]volumeMounts:- name: workdirmountPath: /mnt/vol- name: print-messagecontainer:image: alpine:latestcommand: [sh, -c]args: ["echo getting message from volume; find /mnt/vol; cat /mnt/vol/hello_world.txt"]volumeMounts:- name: workdirmountPath: /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-examplevolumes:# Pass my-existing-volume as an argument to the volumes-existing-example template# Same syntax as k8s Pod spec- name: workdirpersistentVolumeClaim: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: whalesaycontainer:image: docker/whalesay:latestcommand: [sh, -c]args: ["echo generating message in volume; cowsay hello world | tee /mnt/vol/hello_world.txt"]volumeMounts:- name: workdirmountPath: /mnt/vol- name: print-messagecontainer:image: alpine:latestcommand: [sh, -c]args: ["echo getting message from volume; find /mnt/vol; cat /mnt/vol/hello_world.txt"]volumeMounts:- name: workdirmountPath: /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
