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如何分析Knative Eventing中的Sequence及其4 種使用場景，很多新手對此不是很清楚，為了幫助大家解決這個(gè)難題，下面小編將為大家詳細(xì)講解，有這方面需求的人可以來學(xué)習(xí)下，希望你能有所收獲。
導(dǎo)讀：在實(shí)際的開發(fā)中我們經(jīng)常會遇到將一條數(shù)據(jù)需要經(jīng)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(shí)從 Knative Eventing 0.7 版本開始，就提供了 Sequence CRD 資源，用于事件處理 Pipeline。下面將為大家詳細(xì)介紹 Sequence 的定義及在 Knative Eventing 中提供的 4 種使用場景。
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/v1alpha1 kind: InMemoryChannel steps: - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: test reply: kind: Broker apiVersion: eventing.knative.dev/v1alpha1 name: test
Sequence Spec 包括 3 個(gè)部分：
steps： 在 step 中定義了按照順序執(zhí)行的服務(wù)，每個(gè)服務(wù)會對應(yīng)創(chuàng)建 Subscription；
channelTemplate：指定了使用具體的那個(gè) Channel；
reply：（可選）定義了將最后一個(gè) step 服務(wù)結(jié)果轉(zhuǎn)發(fā)到的目標(biāo)服務(wù)。
Sequence 都是適合哪些具體應(yīng)用場景呢？我們上面也提到了事件處理的 Pipeline。那么在實(shí)際場景應(yīng)用中究竟以什么樣的形式體現(xiàn)呢？ 現(xiàn)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(lián) Sequence；
面向 Broker/Trigger。
事件源產(chǎn)生的事件直接發(fā)送給 Sequence 服務(wù)， Sequence 接收到事件之后順序調(diào)用 Service 服務(wù)對事件進(jìn)行處理：
這里我們創(chuàng)建 3 個(gè) Knative Service 用于事件處理。每個(gè) Service 接收到事件之后會打印當(dāng)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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "2" ---
創(chuàng)建順序調(diào)用 first->second->third Service 的 Sequence。
apiVersion: messaging.knative.dev/v1alpha1 kind: Sequence metadata: name: sequence spec: channelTemplate: apiVersion: messaging.knative.dev/v1alpha1 kind: InMemoryChannel steps: - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: first - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: second - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: third
創(chuàng)建 CronJobSource 數(shù)據(jù)源，每隔 1 分鐘發(fā)送一條事件消息 {"message": "Hello world!"} 到 Sequence 服務(wù)。
apiVersion: sources.eventing.knative.dev/v1alpha1
kind: CronJobSource
metadata:
name: cronjob-source
spec:
schedule: "*/1 * * * *"
data: '{"message": "Hello world!"}'
sink:
apiVersion: messaging.knative.dev/v1alpha1
kind: Sequence
name: sequence
事件源產(chǎn)生的事件直接發(fā)送給 Sequence 服務(wù)， Sequence 接收到事件之后順序調(diào)用 Service 服務(wù)對事件進(jìn)行處理，處理之后的最終結(jié)果會調(diào)用 event-display Service 顯示： 
同上創(chuàng)建 3 個(gè) 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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "2" ---
創(chuàng)建順序調(diào)用 first->second->third Service 的 Sequence，將處理結(jié)果通過 reply 發(fā)送給 event-display：
apiVersion: messaging.knative.dev/v1alpha1 kind: Sequence metadata: name: sequence spec: channelTemplate: apiVersion: messaging.knative.dev/v1alpha1 kind: InMemoryChannel steps: - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: first - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: second - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: third reply: kind: Service apiVersion: serving.knative.dev/v1alpha1 name: event-display
創(chuàng)建 event-display Service, 用于接收最終的結(jié)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(chuàng)建 CronJobSource 數(shù)據(jù)源，每隔 1 分鐘發(fā)送一條事件消息 {"message": "Hello world!"} 到 Sequence 服務(wù)。
apiVersion: sources.eventing.knative.dev/v1alpha1
kind: CronJobSource
metadata:
name: cronjob-source
spec:
schedule: "*/1 * * * *"
data: '{"message": "Hello world!"}'
sink:
apiVersion: messaging.knative.dev/v1alpha1
kind: Sequence
name: sequence
Sequence 更高級的地方還在于支持級聯(lián)處理: Sequence By Sequence，這樣可以進(jìn)行多次 Sequence 處理，滿足復(fù)雜事件處理場景需求。 
創(chuàng)建 6 個(gè) Knative Service 用于事件處理， 前 3 個(gè)用于第 1 個(gè) Sequence，后 3 個(gè)用于第 2 個(gè) 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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "5" ---
使用 first->second->third Service 用于第 1 個(gè) Sequence 調(diào)用處理，將執(zhí)行結(jié)果發(fā)送給第 2 個(gè) Sequence。
apiVersion: messaging.knative.dev/v1alpha1 kind: Sequence metadata: name: first-sequence spec: channelTemplate: apiVersion: messaging.knative.dev/v1alpha1 kind: InMemoryChannel steps: - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: first - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: second - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: third reply: kind: Sequence apiVersion: messaging.knative.dev/v1alpha1 name: second-sequence
使用 fourth->fifth->sixth Service 用于第 2 個(gè) Sequence 調(diào)用處理，將執(zhí)行結(jié)果發(fā)送給 event-display。
apiVersion: messaging.knative.dev/v1alpha1 kind: Sequence metadata: name: second-sequence spec: channelTemplate: apiVersion: messaging.knative.dev/v1alpha1 kind: InMemoryChannel steps: - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: fourth - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: fifth - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: sixth reply: kind: Service apiVersion: serving.knative.dev/v1alpha1 name: event-display
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
apiVersion: sources.eventing.knative.dev/v1alpha1
kind: CronJobSource
metadata:
name: cronjob-source
spec:
schedule: "*/1 * * * *"
data: '{"message": "Hello world!"}'
sink:
apiVersion: messaging.knative.dev/v1alpha1
kind: Sequence
name: first-sequence
事件源 cronjobsource 向 Broker 發(fā)送事件，通過 Trigger 將這些事件發(fā)送到由 3 個(gè) Service 調(diào)用的 Sequence 中。Sequence 處理完之后將結(jié)果事件發(fā)送給 Broker，并最終由另一個(gè) Trigger 發(fā)送給 event-display Service 顯示事件結(jié)果:
同上創(chuàng)建 3 個(gè) Knative Service，用于 Sequence 中服務(wù)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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "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:2656f39a7fcb6afd9fc79e7a4e215d14d651dc674f38020d1d18c6f04b220700 env: - name: STEP value: "2" ---
創(chuàng)建 Sequence，這里依次順序執(zhí)行 first->second->third 這 3 個(gè)服務(wù)。將最終處理的結(jié)果發(fā)送到 broker-test 中。
apiVersion: messaging.knative.dev/v1alpha1 kind: Sequence metadata: name: sequence spec: channelTemplate: apiVersion: messaging.knative.dev/v1alpha1 kind: InMemoryChannel steps: - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: first - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: second - ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: third reply: kind: Broker apiVersion: eventing.knative.dev/v1alpha1 name: default
創(chuàng)建 CronjobSource，它將每隔 1 分鐘發(fā)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/v1alpha1
kind: Broker
name: default創(chuàng)建默認(rèn) Broker：
kubectl label namespace default knative-eventing-injection=enabled
創(chuàng)建訂閱事件類型為 dev.knative.cronjob.event 的 Trigger, 用于 Sequence 進(jìn)行消費(fèi)處理。
apiVersion: eventing.knative.dev/v1alpha1 kind: Trigger metadata: name: sequence-trigger spec: filter: sourceAndType: type: dev.knative.cronjob.event subscriber: ref: apiVersion: messaging.knative.dev/v1alpha1 kind: Sequence name: sequence
創(chuàng)建訂閱 samples.http.mod3 的事件類型 Trigger，將 Sequence 執(zhí)行的結(jié)果發(fā)送給 event-display Service 進(jìn)行顯示。
apiVersion: eventing.knative.dev/v1alpha1 kind: Trigger metadata: name: display-trigger spec: filter: sourceAndType: type: samples.http.mod3 subscriber: ref: apiVersion: serving.knative.dev/v1alpha1 kind: Service name: 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 ---
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