[译] 使用CloudEvents和CloudEvents生成器

英文原文来自 Using CloudEvents and CloudEvents Generator,作者 Ratros Y.,文章发表于2019年9月。


本文档讨论了CloudEvents和CloudEvents Generator的使用方法,帮助更好地理解本教程系列其他教程中使用的演示项目,这是 《构建事件驱动的云应用和服务》系列教程的第二篇。

CloudEvents

CloudEvents是由云原生计算基金会的serverless工作组组织的一个倡议,其目标是规范事件发布者如何描述他们的事件。目前这个倡议还在努力中,规范还没有稳定下来;许多云服务提供商和开源项目已经宣布了采用这个规范的计划,包括Knative Eventing和Azure。

备注

您可以在这里阅读 最新版本的规范(0.3)

CloudEvent 由许多属性组成,例如事件的 ID 和事件的类型。CloudEvent Specification 定义了 CloudEvent 可能具有的必要和可选属性集合,如下所示:

Attribute Name 类型 备注
id String Required. The ID of the event. A CloudEvent is uniquely identified with its source and id.
source String (URI-reference) Required. The source of the event.
specversion String Required. The version of CloudEvents Specification the Cloud Event uses.
type String Required. The type of the event.
datacontentencoding String (RFC 2045 Section 6.1) Optional. The encoding of data (if the field stores binary data).
datacontenttype String (RFC 2046) Optional. The content type of data.
schemaurl String (URI-reference) Optional. The schema of data.
subject String Optional. The subject of the event.
time String (Timestamp) Optional. The timestamp when the event happens.
data N/A Optional. The payload of the event.

此外,CloudEvents 允许开发人员通过扩展来添加自己的属性集。文档化的扩展列表可在这里获得.

CloudEvents 绑定有助于在应用、服务和设备之间传输事件。例如,您可以将事件绑定到 JSON 格式,或者将其映射到 HTTP 请求。

CloudEvents 生成器

Normally, to build a CloudEvent, you will have to use an in-memory structure of your preferred programming language directly, or uses CloudEvents SDK (also a work in progress):

通常情况下,要构建一个CloudEvent,需要直接使用自己喜欢的编程语言的内存结构,或者使用CloudEvents SDK(也在进行中):

import datetime
import json
import uuid

event = {}
event['id'] = str(uuid.uuid4())
event['source'] = 'my-event-source'
event[type] = 'my-event-type'
event['specversion'] = '0.3'
event['time'] = datetime.datetime.utcnow().isoformat('T') + 'Z'
event['data'] = 'Hello World!'
event_json_str = json.dumps(event)

# Alternatively with Cloud Events SDK
from cloudevents.sdk.event import v03

event = (
	v03.Event().
	SetEventID('my-event-id').
	SetSource('my-event-source').
	SetEventType('my-event-type').
	SetEventTime(datetime.datetime.utcnow().isoformat('T') + 'Z').
	SetData('Hello World!')
)

在本系列教程中,为了简单起见,我们使用一个实验性的项目CloudEvents Generator来发布和接收事件。该工具以JSON或YAML格式的事件模式作为输入,并准备一个自己的事件schema,你可以用它来发布和接收事件。schema输入和事件库也可以帮助团队在事件驱动的系统中更好地协作。例如,要用CloudEvents Generator发送上述片段中的事件,首先指定 schema 如下:

events:
  # Define an event type, basic
  basic:
    attributes:
      # Set up an attribute id which is auto-poulated with UUIDv4 string
      id:
        type: string
        format: UUIDv4
        auto: true
      # Set up an attribute source with a default value
      source:
        type: string
        default: my-event-source
      # Set up an attribute type with a default value
      type:
        type: string
        default: my-event-type
      # Set up an attribute specversion with a default value
      specversion:
        type: string
        default: "0.3"
      # Set up an attribute time which is auto-populated with RFC3339 timestamp
      time:
        type: string
        format: RFC3339
        auto: true
      # Set up an attribute data
      data:
        type: string

Pass the schema to CloudEvents Generator, and ask it to prepare a Python package. You can then use this package to create the same event:

将模式传给CloudEvents Generator,并要求它准备Python包。然后你可以使用这个包来创建同样的事件:

from mypackage import Basic

# Attributes id and time will be auto-populated
# If not specified, attributes source, type, and specversion use their respective default values
event = Basic(data = 'Hello World!')
event_json_str = event.to_JSON()

要查看CloudEvents Generator的运行情况,请点击下面的按钮在Cloud Shell中试用。

译者注:实操环节请在原文中操作。

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敖小剑
中年码农

我目前研究的方向主要在Microservice、Servicemesh、Serverless等和Cloud Native相关的领域,欢迎交流和指导

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