Event triggered functions in GCP - Deep Dive

Overview - Event triggered functions

What is it?

Event triggered functions are small pieces of code that run automatically when something happens in the cloud. Instead of running all the time, they wait quietly until an event, like a file upload or a message arrival, tells them to start. This helps save resources and makes cloud apps more responsive. They are a key part of serverless computing, where you don't manage servers directly.

Why it matters

Without event triggered functions, cloud apps would need to constantly check for changes or run all the time, wasting money and power. These functions let apps react instantly to real-world actions, like a photo upload or a database update, making apps faster and cheaper. They also simplify building complex workflows by connecting different cloud services automatically.

Where it fits

Before learning event triggered functions, you should understand basic cloud services and how cloud storage or messaging works. After this, you can explore building full serverless applications, combining multiple event triggers, and managing function scaling and security.

Mental Model

Core Idea

Event triggered functions are like automatic helpers that wake up and work only when something specific happens in the cloud.

Think of it like...

Imagine a doorbell at your house. The doorbell (event) rings only when a visitor arrives, and then you respond by opening the door (function runs). You don't stand by the door all day waiting; you only act when the bell rings.

┌───────────────┐       event happens       ┌────────────────────┐
│ Cloud Service │ ─────────────────────────▶ │ Event Triggered Fn │
└───────────────┘                           └────────────────────┘
          ▲                                            │
          │                                            ▼
   event source                                function runs
   (e.g., file upload, message)               (process data, update)

Build-Up - 7 Steps

1

Foundation

What are event triggered functions

Concept: Introduce the basic idea of functions that run automatically on events.

Event triggered functions are small programs that run only when something happens in the cloud. For example, when a file is uploaded to storage or a message arrives in a queue, the function wakes up and runs. This means you don't have to run code all the time, saving resources.

Result

You understand that these functions wait silently and run only when triggered by specific events.

Knowing that functions can be passive until triggered helps you see how cloud resources are used efficiently.

2

Foundation

Common event sources in GCP

Concept: Learn about typical cloud events that can trigger functions in Google Cloud Platform.

In GCP, events can come from many places: Cloud Storage (like file uploads), Pub/Sub messages (like notifications), Firebase events, or Cloud Audit Logs. Each event type carries information that the function can use to decide what to do.

Result

You can identify which cloud services can start your function and what kind of events they send.

Understanding event sources helps you design functions that respond to real-world cloud activities.

3

Intermediate

How to write and deploy event functions

🤔Before reading on: do you think you must manage servers to run event triggered functions, or does the cloud handle that for you? Commit to your answer.

Concept: Learn the process of coding and deploying event triggered functions without managing servers.

You write your function code in supported languages like Python or Node.js. Then, you deploy it to Google Cloud Functions, specifying which event source triggers it. The cloud automatically runs your code when the event happens, handling all server management.

Result

You can create and deploy a function that runs on a chosen event without worrying about servers.

Knowing that the cloud manages servers lets you focus on code logic and event handling, speeding development.

4

Intermediate

Event data and context handling

🤔Before reading on: do you think event triggered functions receive only the event name, or do they get detailed data about the event? Commit to your answer.

Concept: Understand how functions receive event details and context to act appropriately.

When triggered, the function receives event data, like file name or message content, and context, like event time or ID. This information lets the function decide what to do, such as processing a specific file or logging an event.

Result

You can write functions that use event details to perform meaningful actions.

Understanding event data structure is key to writing functions that respond correctly to different triggers.

5

Intermediate

Chaining functions with events

🤔Before reading on: do you think event triggered functions can start other functions automatically, or must all logic be in one function? Commit to your answer.

Concept: Learn how functions can trigger other functions by emitting events, creating workflows.

Functions can produce events that trigger other functions, forming chains or workflows. For example, uploading a file triggers function A, which processes it and publishes a message that triggers function B. This breaks complex tasks into smaller steps.

Result

You can design multi-step processes using event chains for better organization and scalability.

Knowing how to chain functions helps build modular, maintainable cloud applications.

6

Advanced

Scaling and concurrency of event functions

🤔Before reading on: do you think event triggered functions run one at a time or can multiple instances run simultaneously? Commit to your answer.

Concept: Understand how cloud functions scale automatically to handle many events at once.

Google Cloud Functions automatically creates multiple instances of your function to handle many events in parallel. This means your app can handle sudden spikes in activity without delay. However, you must design functions to be stateless and idempotent to avoid issues.

Result

You can build functions that scale smoothly and handle many events without errors.

Understanding automatic scaling and its requirements prevents common bugs and performance problems.

7

Expert

Event delivery guarantees and retries

🤔Before reading on: do you think event triggered functions always run exactly once per event, or can they run multiple times? Commit to your answer.

Concept: Learn about how events are delivered and what happens if a function fails to process an event.

GCP event functions usually have 'at least once' delivery, meaning an event might trigger the function multiple times if retries happen. If a function fails, the event is retried automatically. You must design functions to handle repeated events safely to avoid duplicate work or errors.

Result

You can write robust functions that handle retries and avoid problems from repeated events.

Knowing delivery guarantees helps you build reliable, fault-tolerant cloud functions.

Under the Hood

When an event occurs in a cloud service, it sends a message to the event system. This system routes the event to the registered function's runtime environment. The cloud platform spins up a container or uses an existing one to run the function code with the event data. After execution, the environment may stay warm for future events or shut down to save resources.

Why designed this way?

This design allows efficient use of resources by running code only when needed, avoiding idle servers. It also simplifies scaling, as the platform can create many function instances on demand. Alternatives like always-on servers waste resources and require manual scaling.

┌───────────────┐   event occurs   ┌───────────────┐   routes event   ┌───────────────┐
│ Cloud Service │ ───────────────▶ │ Event System  │ ───────────────▶ │ Function Run  │
└───────────────┘                 └───────────────┘                 └───────────────┘
                                      │                                  │
                                      │                                  ▼
                                manages queues                     executes code
                                and retries

Myth Busters - 4 Common Misconceptions

Quick: Do event triggered functions run continuously in the background? Commit to yes or no.

Common Belief: Event triggered functions run all the time waiting for events.

Reality: They do not run continuously; they start only when an event happens.

Why it matters: Believing they run always can lead to overestimating costs and misunderstanding how serverless works.

Quick: Do you think event triggered functions always run exactly once per event? Commit to yes or no.

Common Belief: Each event triggers the function exactly once, no repeats.

Reality: Events may trigger functions multiple times due to retries or delivery guarantees.

Why it matters: Ignoring this can cause duplicate processing and data errors if functions are not designed for idempotency.

Quick: Can event triggered functions maintain state between runs? Commit to yes or no.

Common Belief: Functions can keep data in memory between event runs.

Reality: Functions are stateless; any state must be stored externally.

Why it matters: Assuming state is kept leads to bugs and inconsistent behavior in scaled environments.

Quick: Do you think event triggered functions require manual server management? Commit to yes or no.

Common Belief: You must manage servers and scaling for event triggered functions.

Reality: The cloud platform manages servers and scaling automatically.

Why it matters: Misunderstanding this wastes time and effort on unnecessary infrastructure tasks.

Expert Zone

1

Event functions can have cold starts causing initial delay; understanding how to minimize cold starts improves user experience.

2

Some event sources have different delivery guarantees; knowing these helps design correct retry and error handling strategies.

3

Function execution time limits require careful design of long-running workflows, often needing orchestration services.

When NOT to use

Event triggered functions are not ideal for long-running tasks or those needing guaranteed exactly-once processing. For such cases, use managed workflow services like Cloud Workflows or dedicated message queues with transactional processing.

Production Patterns

In production, event functions are used for image processing on upload, real-time data pipelines, automated backups, and microservice communication. They are often combined with monitoring and alerting to handle failures gracefully.

Connections

Reactive programming

Event triggered functions embody reactive programming principles by responding to data changes or events.

Understanding reactive programming helps grasp how event functions react instantly to cloud events, enabling responsive systems.

Interrupt handling in operating systems

Both event triggered functions and OS interrupts respond to signals to run code immediately.

Knowing OS interrupts clarifies how event functions are efficient by running only when needed, not polling continuously.

Supply chain logistics

Event triggered functions resemble just-in-time delivery triggered by demand signals in logistics.

Seeing event functions as just-in-time responders helps understand resource efficiency and responsiveness in cloud computing.

Common Pitfalls

#1 Writing functions that assume they run only once per event.

Wrong approach:

def process_event(event):
if event['id'] in processed_ids:
return
processed_ids.add(event['id'])
# process event

Correct approach:

def process_event(event):
# Use external storage or idempotent operations to handle duplicates
# e.g., update database with upsert or check external state
pass

Root cause:

Assuming in-memory state persists across function runs, ignoring retries and multiple instances.

#2 Trying to keep user session or data in function memory between events.

Wrong approach:

session_data = {}
def handle_event(event):
session_data[event['user']] = event['data']
# use session_data later

Correct approach:

def handle_event(event):
# Store session data in external database or cache
pass

Root cause:

Misunderstanding that functions are stateless and memory is not shared or persistent.

#3 Deploying functions without specifying correct event triggers.

Wrong approach:

gcloud functions deploy myFunc --runtime python39 --trigger-http
# but expecting it to run on file upload events

Correct approach:

gcloud functions deploy myFunc --runtime python39 --trigger-resource my-bucket --trigger-event google.storage.object.finalize

Root cause:

Confusing HTTP triggers with event triggers and not configuring triggers properly.

Key Takeaways

Event triggered functions run only when specific cloud events happen, saving resources and enabling reactive apps.

They receive detailed event data and context, allowing precise and meaningful responses to cloud activities.

The cloud platform manages scaling and servers automatically, but functions must be stateless and idempotent.

Events may trigger functions multiple times, so functions must handle retries and duplicates safely.

Chaining event functions enables building complex workflows by connecting simple, focused functions.