Eventarc Complete Guide: CloudEvents, 90+ Event Sources & Serverless Triggers

Eventarc is GCP's unified event routing platform, delivering events from 90+ services in the CloudEvents standard format to Cloud Run / Cloud Functions / Workflows / GKE. It can be thought of as the central nervous system for event-driven architectures on GCP.

Core Concepts

• Trigger: Routing rule from event source to target
• Event Provider: The event origin (Cloud Audit Logs / GCS / Pub/Sub, etc.)
• Destination: The event delivery target (Cloud Run / Functions / Workflows)
• CloudEvents: CNCF standard event metadata spec
• Filter: Filter by type / serviceName / methodName

Key Event Sources

Trigger Creation Examples

# GCS バケットアップロード → Cloud Run トリガー
gcloud eventarc triggers create my-trigger \
  --location=asia-northeast1 \
  --destination-run-service=image-processor \
  --destination-run-region=asia-northeast1 \
  --event-filters="type=google.cloud.storage.object.v1.finalized" \
  --event-filters="bucket=my-upload-bucket" \
  [email protected]

# Audit Log → Cloud Functions (特定操作)
gcloud eventarc triggers create iam-audit-trigger \
  --location=asia-northeast1 \
  --destination-run-service=audit-handler \
  --event-filters="type=google.cloud.audit.log.v1.written" \
  --event-filters="serviceName=iam.googleapis.com" \
  --event-filters="methodName=google.iam.admin.v1.SetIamPolicy"

CloudEvents Format

{
  "specversion": "1.0",
  "id": "12345-abcde",
  "source": "//storage.googleapis.com/projects/_/buckets/my-bucket",
  "type": "google.cloud.storage.object.v1.finalized",
  "datacontenttype": "application/json",
  "subject": "objects/photo.jpg",
  "time": "2026-05-24T10:00:00.000Z",
  "data": {
    "bucket": "my-bucket",
    "name": "photo.jpg",
    "size": "1024000",
    "contentType": "image/jpeg"
  }
}

Receiver Code Example (Cloud Run / Python)

from cloudevents.http import from_http
from flask import Flask, request

app = Flask(__name__)

@app.route("/", methods=["POST"])
def handle_event():
    event = from_http(request.headers, request.get_data())
    print(f"Event ID: {event['id']}")
    print(f"Event Type: {event['type']}")
    print(f"Data: {event.data}")
    # 処理ロジック
    return ("", 204)

Pricing

• Eventarc itself: Free
• Underlying Pub/Sub: $40/TB (first 6 GB/month free)
• Targets (Cloud Run / Functions): per-service pricing
• Effectively near-free even for large-scale usage

Comparison with Other Clouds

Typical Use Cases

• GCS upload → image resize / OCR / ML inference
• BigQuery query completion → notification / next-step trigger
• IAM change audit → security notification (Audit Log → Cloud Functions)
• Firestore change → Algolia index update
• Vertex AI training completion → model evaluation / deployment
• Cloud Build completion → Cloud Deploy release creation

* Google Cloud is a trademark of Google LLC. For the latest information, please refer to the official Eventarc documentation.