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Post to Slack

A callable workflow that posts a message to a Slack channel via an incoming webhook. The webhook URL is sensitive — store it in H2O Secure Store and pass it in as a secret input (secret: true), so the value is redacted from logs.

Workflow​

id: notify-slack
name: Post Message to Slack

trigger:
  callable: true

inputs:
  webhook_url:
    type: string
    required: true
    secret: true
    description: "Slack incoming webhook URL"
  message:
    type: string
    required: true
    description: "Message text to post"
  channel:
    type: string
    default: ""
    description: "Override channel (optional, uses webhook default if empty)"
  username:
    type: string
    default: "H2O Workflows"
    description: "Bot username displayed in Slack"

jobs:
  post:
    name: "Post to Slack"
    timeout: "1m"
    steps:
      - name: "Send Slack notification"
        env:
          WEBHOOK_URL: "${{ .inputs.webhook_url }}"
          MESSAGE: "${{ .inputs.message }}"
          CHANNEL: "${{ .inputs.channel }}"
          USERNAME: "${{ .inputs.username }}"
        run: |
          python3 -c "
          import os, json, urllib.request

          payload = {
              'text': os.environ['MESSAGE'],
              'username': os.environ['USERNAME'],
          }
          if os.environ.get('CHANNEL'):
              payload['channel'] = os.environ['CHANNEL']

          req = urllib.request.Request(
              os.environ['WEBHOOK_URL'],
              data=json.dumps(payload).encode(),
              headers={'Content-Type': 'application/json'},
          )
          resp = urllib.request.urlopen(req)
          print(f'Slack response: {resp.status} {resp.read().decode()}')
          "

Calling it from your workflow​

Reference your stored secret with ${{ .secrets.<name> }}:

secrets:
  - name: workspaces/<workspace-id>/secrets/slack-webhook
    as: slack_webhook

jobs:
  notify:
    workflow:
      name: notify-slack
      inputs:
        webhook_url: "${{ .secrets.slack_webhook }}"
        message: "Workflow finished successfully"
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