作者 | 元毅，阿里云容器平臺高級開發工程師，負責阿里云容器平臺 Knative 相關工作。

導讀：在實際的開發中我們經常會遇到將一條數據需要經過多次處理的場景，稱為 Pipeline。那么在 Knative 中是否也提供這樣的能力呢？其實從 Knative Eventing 0.7 版本開始，就提供了 Sequence CRD 資源，用于事件處理 Pipeline。本篇文章中，阿里云容器平臺高級開發工程師元毅將為大家詳細介紹 Sequence 的定義及在 Knative Eventing 中提供的 4 種使用場景。

Sequence 定義

首先來看一下 Sequence Spec 定義：

apiVersion: messaging.knative.dev/v1alpha1
kind: Sequence
metadata:name: test
spec:channelTemplate:apiVersion: messaging.knative.dev/v1alpha1kind: InMemoryChannelsteps:- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: testreply:kind: BrokerapiVersion: eventing.knative.dev/v1alpha1name: test

Sequence Spec 包括 3 個部分：

1. steps： 在 step 中定義了按照順序執行的服務，每個服務會對應創建 Subscription；

2. channelTemplate：指定了使用具體的那個 Channel；

3. reply：（可選）定義了將最后一個 step 服務結果轉發到的目標服務。

   Sequence 都是適合哪些具體應用場景呢？我們上面也提到了事件處理的 Pipeline。那么在實際場景應用中究竟以什么樣的形式體現呢？ 現在我們揭曉一下 Sequence 在 Knative Eventing 中提供的如下 4 種使用場景：

• 直接訪問 Service；
• 面向事件處理；
• 級聯 Sequence；
• 面向 Broker/Trigger。

直接訪問 Service 場景

事件源產生的事件直接發送給 Sequence 服務， Sequence 接收到事件之后順序調用 Service 服務對事件進行處理：

創建 Knative Service

這里我們創建 3 個 Knative Service 用于事件處理。每個 Service 接收到事件之后會打印當前的事件處理信息。

apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: first
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "0"---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: second
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "1"
---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: third
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "2"
---

創建 Sequence

創建順序調用 first->second->third Service 的 Sequence。

apiVersion: messaging.knative.dev/v1alpha1
kind: Sequence
metadata:name: sequence
spec:channelTemplate:apiVersion: messaging.knative.dev/v1alpha1kind: InMemoryChannelsteps:- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: first- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: second- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: third

創建數據源

創建 CronJobSource 數據源，每隔 1 分鐘發送一條事件消息 {"message": "Hello world!"} 到 Sequence 服務。

apiVersion: sources.eventing.knative.dev/v1alpha1
kind: CronJobSource
metadata:name: cronjob-source
spec:schedule: "*/1 * * * *"data: '{"message": "Hello world!"}'sink:apiVersion: messaging.knative.dev/v1alpha1kind: Sequencename: sequence

示例結果

面向事件處理場景

事件源產生的事件直接發送給 Sequence 服務， Sequence 接收到事件之后順序調用 Service 服務對事件進行處理，處理之后的最終結果會調用 event-display Service 顯示：

創建 Knative Service

同上創建 3 個 Knative Service 用于事件處理：

apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: first
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "0"---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: second
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "1"
---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: third
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "2"
---

創建 Sequence

創建順序調用 first->second->third Service 的 Sequence，將處理結果通過 reply 發送給 event-display：

apiVersion: messaging.knative.dev/v1alpha1
kind: Sequence
metadata:name: sequence
spec:channelTemplate:apiVersion: messaging.knative.dev/v1alpha1kind: InMemoryChannelsteps:- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: first- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: second- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: thirdreply:kind: ServiceapiVersion: serving.knative.dev/v1alpha1name: event-display

創建結果顯示 Service

創建 event-display Service, 用于接收最終的結果信息。

apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: event-display
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-release/event_display:bf45b3eb1e7fc4cb63d6a5a6416cf696295484a7662e0cf9ccdf5c080542c21d

創建數據源

創建 CronJobSource 數據源，每隔 1 分鐘發送一條事件消息 {"message": "Hello world!"} 到 Sequence 服務。

apiVersion: sources.eventing.knative.dev/v1alpha1
kind: CronJobSource
metadata:name: cronjob-source
spec:schedule: "*/1 * * * *"data: '{"message": "Hello world!"}'sink:apiVersion: messaging.knative.dev/v1alpha1kind: Sequencename: sequence

示例結果

級聯 Sequence 場景

Sequence 更高級的地方還在于支持級聯處理: Sequence By Sequence，這樣可以進行多次 Sequence 處理，滿足復雜事件處理場景需求。

創建 Knative Service

創建 6 個 Knative Service 用于事件處理， 前 3 個用于第 1 個 Sequence，后 3 個用于第 2 個 Sequence。

apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: first
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "0"---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: second
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "1"
---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: third
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "2"
---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: fourth
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "3"---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: fifth
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "4"
---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: sixth
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "5"
---

創建第 1 個 Sequence

使用 first->second->third Service 用于第 1 個 Sequence 調用處理，將執行結果發送給第 2 個 Sequence。

apiVersion: messaging.knative.dev/v1alpha1
kind: Sequence
metadata:name: first-sequence
spec:channelTemplate:apiVersion: messaging.knative.dev/v1alpha1kind: InMemoryChannelsteps:- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: first- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: second- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: thirdreply:kind: SequenceapiVersion: messaging.knative.dev/v1alpha1name: second-sequence

創建第 2 個 Sequence

使用 fourth->fifth->sixth Service 用于第 2 個 Sequence 調用處理，將執行結果發送給 event-display。

apiVersion: messaging.knative.dev/v1alpha1
kind: Sequence
metadata:name: second-sequence
spec:channelTemplate:apiVersion: messaging.knative.dev/v1alpha1kind: InMemoryChannelsteps:- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: fourth- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: fifth- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: sixthreply:kind: ServiceapiVersion: serving.knative.dev/v1alpha1name: event-display

創建結果顯示 Service

apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: event-display
spec:template:spec:containerers:- image: registry.cn-hangzhou.aliyuncs.com/knative-release/event_display:bf45b3eb1e7fc4cb63d6a5a6416cf696295484a7662e0cf9ccdf5c080542c21d

創建數據源指向第 1 個 Sequence

apiVersion: sources.eventing.knative.dev/v1alpha1
kind: CronJobSource
metadata:name: cronjob-source
spec:schedule: "*/1 * * * *"data: '{"message": "Hello world!"}'sink:apiVersion: messaging.knative.dev/v1alpha1kind: Sequencename: first-sequence

示例結果

Broker/Trigger 場景

事件源 cronjobsource 向 Broker 發送事件，通過 Trigger 將這些事件發送到由 3 個 Service 調用的 Sequence 中。Sequence 處理完之后將結果事件發送給 Broker，并最終由另一個 Trigger 發送給 event-display Service 顯示事件結果:

創建 Knative Service

同上創建 3 個 Knative Service，用于 Sequence 中服務處理。

apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: first
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "0"---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: second
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "1"
---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: third
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-sample/probable-summer:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700env:- name: STEPvalue: "2"---

創建 Sequence

創建 Sequence，這里依次順序執行 first->second->third 這 3 個服務。將最終處理的結果發送到 broker-test 中。

apiVersion: messaging.knative.dev/v1alpha1
kind: Sequence
metadata:name: sequence
spec:channelTemplate:apiVersion: messaging.knative.dev/v1alpha1kind: InMemoryChannelsteps:- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: first- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: second- ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: thirdreply:kind: BrokerapiVersion: eventing.knative.dev/v1alpha1name: default

創建事件源指向 Broker

創建 CronjobSource，它將每隔 1 分鐘發送一條 {"message": "Hello world!"} 消息到 broker-test 中。

apiVersion: sources.eventing.knative.dev/v1alpha1
kind: CronJobSource
metadata:name: cronjob-source
spec:schedule: "*/1 * * * *"data: '{"message": "Hello world!"}'sink:apiVersion: eventing.knative.dev/v1alpha1kind: Brokername: default

創建 Broker

創建默認 Broker：

kubectl label namespace default knative-eventing-injection=enabled

創建 Trigger 指向 Sequence

創建訂閱事件類型為 dev.knative.cronjob.event 的 Trigger, 用于 Sequence 進行消費處理。

apiVersion: eventing.knative.dev/v1alpha1
kind: Trigger
metadata:name: sequence-trigger
spec:filter:sourceAndType:type: dev.knative.cronjob.eventsubscriber:ref:apiVersion: messaging.knative.dev/v1alpha1kind: Sequencename: sequence

創建結果訂閱 Trigger

創建訂閱 samples.http.mod3 的事件類型 Trigger，將 Sequence 執行的結果發送給 event-display Service 進行顯示。

apiVersion: eventing.knative.dev/v1alpha1
kind: Trigger
metadata:name: display-trigger
spec:filter:sourceAndType:type: samples.http.mod3subscriber:ref:apiVersion: serving.knative.dev/v1alpha1kind: Servicename: event-display
---
apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:name: event-display
spec:template:spec:containers:- image: registry.cn-hangzhou.aliyuncs.com/knative-release/event_display:bf45b3eb1e7fc4cb63d6a5a6416cf696295484a7662e0cf9ccdf5c080542c21d
---

示例結果

小結

以上介紹了什么是 Sequence， 以及基于 Sequence 的 4 種使用場景，我們可以根據實際需求選擇不同的使用場景，從而實現事件處理 Pipeline。這對于需要多步驟處理事件的場景尤為適合。

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