Eventarc for event routing in GCP - Step-by-Step Execution

Process Flow - Eventarc for event routing

Event Source emits event

↓

Eventarc receives event

↓

Eventarc matches event to trigger

↓

Eventarc routes event to destination

↓

Destination processes event

Events are sent from a source, Eventarc receives and matches them to triggers, then routes them to the right destination for processing.

Execution Sample

GCP

gcloud eventarc triggers create my-trigger \
  --destination-run-service=my-service \
  --destination-run-region=us-central1 \
  --event-filters="type=google.cloud.storage.object.v1.finalized"

This command creates an Eventarc trigger that routes storage object finalized events to a Cloud Run service.

Process Table

Step	Action	Event Data	Trigger Match	Routing Destination	Result
1	Event Source emits event	{"type":"google.cloud.storage.object.v1.finalized","bucket":"my-bucket"}	N/A	N/A	Event sent to Eventarc
2	Eventarc receives event	{"type":"google.cloud.storage.object.v1.finalized","bucket":"my-bucket"}	Checking triggers	N/A	Event received
3	Eventarc matches event to trigger	{"type":"google.cloud.storage.object.v1.finalized"}	Trigger 'my-trigger' matches	N/A	Match found
4	Eventarc routes event	Event data passed	N/A	Cloud Run service 'my-service' in us-central1	Event routed
5	Destination processes event	Event data received	N/A	Cloud Run service 'my-service'	Event processed successfully
6	No more events	N/A	N/A	N/A	Waiting for next event

💡 No more events to process, Eventarc waits for new events.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
Event Data	None	{"type":"google.cloud.storage.object.v1.finalized","bucket":"my-bucket"}	{"type":"google.cloud.storage.object.v1.finalized","bucket":"my-bucket"}	{"type":"google.cloud.storage.object.v1.finalized"}	Passed to destination	Received by destination	Processed
Trigger Match	None	N/A	Checking triggers	Trigger 'my-trigger' matched	N/A	N/A	N/A
Routing Destination	None	N/A	N/A	N/A	Cloud Run service 'my-service'	Cloud Run service 'my-service'	Cloud Run service 'my-service'

Key Moments - 3 Insights

How does Eventarc know which destination to send the event to?

Eventarc uses triggers that match event attributes like type. In the execution_table row 3, the event type matches the trigger 'my-trigger', so Eventarc routes the event accordingly.

What happens if no trigger matches the event?

If no trigger matches, Eventarc does not route the event to any destination. This is implied by the matching step in execution_table row 3 where no match would mean no routing.

Can Eventarc process multiple event types with one trigger?

No, each trigger filters specific event types. To handle multiple types, you create multiple triggers. This is shown in the event-filters in the execution_sample.

Visual Quiz - 3 Questions

Look at the execution_table, at which step does Eventarc decide where to send the event?

A Step 3

B Step 2

C Step 4

D Step 5

💡 Hint

Check the 'Trigger Match' column in execution_table row 3 where the match is found.

According to variable_tracker, what is the state of 'Event Data' after step 4?

A None

B Matched trigger data

C Passed to destination

D Processed

💡 Hint

Look at the 'Event Data' row under 'After Step 4' in variable_tracker.

If the event type changed to one not matching any trigger, what would happen in the execution_table?

A Eventarc routes event to destination anyway

B No trigger match found, event not routed

C Eventarc matches a different trigger

D Eventarc processes event itself

💡 Hint

Refer to key_moments about what happens if no trigger matches.

Concept Snapshot

Eventarc routes events from sources to destinations using triggers.
Triggers filter events by attributes like type.
When an event matches a trigger, Eventarc routes it to the destination.
Destinations can be Cloud Run, Pub/Sub, or others.
Eventarc waits for events and routes them automatically.

Full Transcript

Eventarc is a service that listens for events from various sources. When an event happens, it sends the event data to Eventarc. Eventarc checks its triggers to find one that matches the event type or other filters. If a trigger matches, Eventarc routes the event to the destination specified in the trigger, such as a Cloud Run service. The destination then processes the event. If no trigger matches, the event is not routed. This process repeats for every event received.

Practice

1. What is the main purpose of Eventarc in Google Cloud?

easy

A. To create virtual machines for running applications

B. To store large amounts of data in the cloud

C. To route events from cloud services to your applications automatically

D. To manage user permissions and roles

Solution

1. Step 1: Understand Eventarc's role

   Eventarc is designed to listen for events from various cloud services and route them to your applications automatically.

2. Step 2: Compare options

   Options A, B, and D describe other cloud services like storage, compute, and IAM, which are not Eventarc's purpose.

3. Final Answer:

   To route events from cloud services to your applications automatically -> Option C

4. Quick Check:

   Event routing = To route events from cloud services to your applications automatically [OK]

Hint: Eventarc = automatic event routing to apps [OK]

Common Mistakes:

• Confusing Eventarc with storage services
• Thinking Eventarc manages virtual machines
• Mixing Eventarc with user permission management

2. Which of the following is the correct way to create an Eventarc trigger using gcloud CLI?

easy

A. gcloud compute instances create my-trigger --zone=us-central1-a

B. gcloud eventarc triggers create my-trigger --destination-run-service=my-service --event-filters=type=google.cloud.pubsub.topic.v1.messagePublished

C. gcloud storage buckets create my-trigger --location=us-central1

D. gcloud iam roles create my-trigger --project=my-project

Solution

1. Step 1: Identify Eventarc trigger creation syntax

   The correct command uses 'gcloud eventarc triggers create' with destination and event filters.

2. Step 2: Eliminate unrelated commands

   Options B, C, and D relate to compute, storage, and IAM, not Eventarc triggers.

3. Final Answer:

   gcloud eventarc triggers create my-trigger --destination-run-service=my-service --event-filters=type=google.cloud.pubsub.topic.v1.messagePublished -> Option B

4. Quick Check:

   Eventarc trigger creation uses 'gcloud eventarc triggers create' [OK]

Hint: Eventarc triggers start with 'gcloud eventarc triggers create' [OK]

Common Mistakes:

• Using compute or storage commands instead of eventarc
• Missing event-filters parameter
• Incorrect destination flag

3. Given this Eventarc trigger configuration snippet:

{
  "name": "projects/my-project/locations/us-central1/triggers/my-trigger",
  "destination": {
    "cloudRunService": {
      "service": "my-service",
      "region": "us-central1"
    }
  },
  "eventFilters": [
    {"attribute": "type", "value": "google.cloud.storage.object.v1.finalized"}
  ]
}

What event will this trigger listen for?

medium

A. New objects finalized (created) in Cloud Storage buckets

B. Messages published to Pub/Sub topics

C. Compute Engine instance start events

D. Cloud SQL database updates

Solution

1. Step 1: Analyze eventFilters attribute

   The filter type is 'google.cloud.storage.object.v1.finalized', which means when a Cloud Storage object is finalized (created or overwritten).

2. Step 2: Match event type to options

   This corresponds to new or updated objects in Cloud Storage buckets, not Pub/Sub, Compute Engine, or Cloud SQL events.

3. Final Answer:

   New objects finalized (created) in Cloud Storage buckets -> Option A

4. Quick Check:

   Storage object finalized event = New objects finalized (created) in Cloud Storage buckets [OK]

Hint: Storage object finalized event type ends with '.finalized' [OK]

Common Mistakes:

• Confusing storage events with Pub/Sub messages
• Assuming compute or database events
• Ignoring eventFilters attribute

4. You created an Eventarc trigger but your Cloud Run service is not receiving events. Which of the following is the most likely cause?

medium

A. The trigger was created with the wrong gcloud project set

B. The Cloud Run service is in a different region than the trigger

C. The Cloud Run service has no CPU allocated

D. The trigger's event filter type does not match any events being emitted

Solution

1. Step 1: Check event filter correctness

   If the event filter type does not match any events, no events will be routed to the service.

2. Step 2: Consider other options

   While region mismatch or wrong project can cause issues, the most common cause is incorrect event filter type. CPU allocation does not prevent event delivery.

3. Final Answer:

   The trigger's event filter type does not match any events being emitted -> Option D

4. Quick Check:

   Event filter mismatch blocks events [OK]

Hint: Check event filter matches actual event types [OK]

Common Mistakes:

• Ignoring event filter mismatch
• Assuming CPU allocation affects event routing
• Not verifying project and region settings

5. You want to build an event-driven app that reacts to both Cloud Storage object creations and Pub/Sub messages using Eventarc. What is the best way to configure triggers?

hard

A. Create two separate Eventarc triggers, one for Cloud Storage events and one for Pub/Sub events, both targeting the same Cloud Run service

B. Create a single Eventarc trigger with multiple event filters for both Cloud Storage and Pub/Sub events

C. Create one trigger for Cloud Storage and configure Pub/Sub to push messages directly to Cloud Run without Eventarc

D. Use Cloud Scheduler to poll both services and send events to Cloud Run

Solution

1. Step 1: Understand Eventarc trigger event filters

   Each Eventarc trigger supports filtering on one event type. To listen to multiple event types, separate triggers are needed.

2. Step 2: Evaluate options

   Create a single Eventarc trigger with multiple event filters for both Cloud Storage and Pub/Sub events is invalid because a single trigger cannot filter multiple event types. Create one trigger for Cloud Storage and configure Pub/Sub to push messages directly to Cloud Run without Eventarc bypasses Eventarc for Pub/Sub, losing unified routing. Use Cloud Scheduler to poll both services and send events to Cloud Run is unrelated to Eventarc and less efficient.

3. Final Answer:

   Create two separate Eventarc triggers, one for Cloud Storage events and one for Pub/Sub events, both targeting the same Cloud Run service -> Option A

4. Quick Check:

   Multiple event types = multiple triggers [OK]

Hint: Use one trigger per event type for multiple events [OK]

Common Mistakes:

• Trying to use one trigger for multiple event types
• Bypassing Eventarc for some events
• Using polling instead of event routing