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Pablo Mercado
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Merge pull request #219 from triggermesh/bridge/webhook-to-slack
Add bridge webhook to slack
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‎docs/guides/bridges/webhook-to-slack.md

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# Writing a Webhook to Slack Bridge
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This Bridge connects an HTTP endpoint to Slack. Every time the webhook is called a message will be produced, which we will validate and transform into an Slack message.
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We will be calling the exposed HTTP endpoint using `curl`, in a real world scenario the caller would be an application configuring a webhook callback.
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## Events
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Webhook Source produce arbitrary events based on configuration and received requests.
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- `type` attribute is set to the one configured by user.
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- `source` attribute is set to the one configured by user.
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- `datacontenttype` is set to the `Content-Type` received at the incoming request.
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- `data` is set to the body of the received request.
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Slack Target expect one of these 3 event types along with their related payload:
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- `com.slack.webapi.chat.postMessage` for consuming [chat.postMessage][chat.postMessage]
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- `com.slack.webapi.chat.scheduleMessage` for consuming [chat.scheduleMessage][chat.scheduleMessage]
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- `com.slack.webapi.chat.update` for consuming [chat.update][chat.update]
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This fictional scenario will send the following data to the Webhook Source using `curl`.
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```json
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{"message": "Hello Slack!"}
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```
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The Webhook Source is expected to produce this event.
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```json
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type: webhook.slack.postmessage
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data: {"message": "Hello Slack!"}
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others: ...
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```
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We will be using TriggerMesh's Function to perform a transformation which will consume the event above and produce this one.
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```json
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type: com.slack.webapi.chat.postMessage
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data: {"channel":"ABCDE12345", "text": "Hello Slack!"}
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others: ...
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```
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This event will finally be consumed by the Slack Target that will in turn call the Slack API to post the message.
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## Webhook Source
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For simplicity we are setting up a non authenticated Webhook and using the default Kubernetes namespace.
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```yaml
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apiVersion: sources.triggermesh.io/v1alpha1
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kind: WebhookSource
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metadata:
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name: post-message
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spec:
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eventType: webhook.slack.postmessage
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eventSource: webhoock.post-message
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sink:
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ref:
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apiVersion: eventing.knative.dev/v1
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kind: Broker
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name: default
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```
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The `eventType` and `eventSource` CloudEvents attributes are being set for further event filtering. There is a reference to a Broker sink object where events will be sent, we will get to that one later.
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## Slack Target
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Slack Target requires:
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- Creating a new [Slack App][slack-apps]: add the `chat:write` permission under `Bot Token Scopes`, then install the application at your workspace.
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- A Slack API token: from the **Install App** menu retrieve the OAuth Access token that begins with `xoxb-`.
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Create a secret using the Slack API token
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```yaml
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apiVersion: v1
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kind: Secret
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metadata:
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name: slack-tm
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type: Opaque
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stringData:
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token: xoxb-12345-abcde
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```
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Create the Slack Target referencing the API token.
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```yaml
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apiVersion: targets.triggermesh.io/v1alpha1
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kind: SlackTarget
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metadata:
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name: slack-tm
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spec:
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token:
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secretKeyRef:
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name: slack-tm
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key: token
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```
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## Transformation Component
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To bridge the gap between the event produced by the Webhook Source and the one expected at the Slack Target we need to perform a transformation, which we can do using a declarative or coded approach. We will use the later here.
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Replace the channel ID in this transformation with the one you want to use. The channel ID can be retrieved from the URL either at the browser or selecting the `copy link` option at the Slack app. Please make sure that the bot user is added to the Slack channel.
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```yaml
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apiVersion: extensions.triggermesh.io/v1alpha1
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kind: Function
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metadata:
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name: webhook-to-slack
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spec:
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runtime: python
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public: false
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entrypoint: transformToSlack
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ceOverrides:
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extensions:
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type: com.slack.webapi.chat.postMessage
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code: |
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from random import randrange
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def transformToSlack(event, context):
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return {
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"channel":"REPLACE-CHANNEL-ID",
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"text": event['message']
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}
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```
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## Routing Components
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In order to connect all components we will setup these elements:
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- A central Broker that receives messages from the Source
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- A Trigger that consumes Webhook events filtered by the `webhook.slack.postmessage` type and sends them to the transformation Function.
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- A Trigger that consumes transformed events filtered by the `com.slack.webapi.chat.postMessage` type and sends them to the Slack target.
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The Broker name is set to `default` to match the one used at the Webhook Source earlier.
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```yaml
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apiVersion: eventing.knative.dev/v1
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kind: Broker
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metadata:
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name: default
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```
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Both Triggers are setup on the Broker and subscribe their corresponding destination filtering by types.
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```yaml
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apiVersion: eventing.knative.dev/v1
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kind: Trigger
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metadata:
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name: wehook-to-transform
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spec:
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broker: default
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filter:
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attributes:
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type: webhook.slack.postmessage
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subscriber:
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ref:
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apiVersion: extensions.triggermesh.io/v1alpha1
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kind: Function
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name: webhook-to-slack
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---
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apiVersion: eventing.knative.dev/v1
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kind: Trigger
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metadata:
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name: slack-post-messages
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spec:
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broker: default
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filter:
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attributes:
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type: com.slack.webapi.chat.postMessage
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subscriber:
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ref:
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apiVersion: targets.triggermesh.io/v1alpha1
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kind: SlackTarget
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name: slack-tm
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```
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## Done
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Retrieve the URL where the Webhook is listening for incoming requests.
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```console
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$ kubectl get webhooksources.sources.triggermesh.io post-message
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NAME READY REASON URL SINK AGE
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post-message True https://webhooksource-post-message.woodford.dev.triggermesh.io http://broker-ingress.knative-eventing.svc.cluster.local/woodford/default 61s
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Use `curl` or any HTTP capable client to post messages at Slack.
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```
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curl -d '{"message":"test my bridge"}' https://webhooksource-post-message.woodford.dev.triggermesh.io
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```
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Thid Bridge can be extended in many different ways:
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- Validation and error handling at the transformation Function.
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- The Channel could be provided as a parameter from the WebhookSource, defaulting to a channel provided by the Function.
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- AWS Comprehend could be used for sentiment analysis.
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- Messages could be enriched if they contain word `avocado` with 🥑
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- Add a Twilio Source that will also feed incoming messages to the Broker.
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- Add a Datadog Target that will convert a subset of filtered messages into alerts.
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If you have any questions on how to build this Bridge or how to modify it to suit your needs, join our [Community Slack](http://triggermesh-community.slack.com/) and [contact us](mailto:[email protected]).
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[chat.postMessage]: https://api.slack.com/methods/chat.postMessage
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[chat.scheduleMessage]: https://api.slack.com/methods/chat.scheduleMessage
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[chat.update]: https://api.slack.com/methods/chat.update
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[slack-apps]: https://api.slack.com/apps
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‎mkdocs.yml

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- Doing a Transformation: guides/doingatransformation.md
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- Writing a Function: guides/writingafunction.md
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- Using TIL: guides/tilgettingstarted.md
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- Bridges:
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- Webhook to Slack: guides/bridges/webhook-to-slack.md
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- Installation:
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- '': guides/installation.md
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- Using an AWS AMI: guides/installation-ami.md

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