Event triggered functions in GCP - Step-by-Step Execution

Process Flow - Event triggered functions

Event Occurs

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Cloud Event Detected

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Trigger Function

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Function Executes

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Function Completes

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Optional: Emit Result or Log

When an event happens in the cloud, it triggers a function to run automatically, which then executes and finishes its task.

Execution Sample

GCP

def hello_gcs(event, context):
    print(f"File {event['name']} uploaded.")

This function runs when a file is uploaded to Cloud Storage and prints the file name.

Process Table

Step	Event	Function Triggered	Action	Output
1	File uploaded to bucket 'photos'	hello_gcs	Function starts	No output yet
2	N/A	hello_gcs	Reads event data: file name 'image1.png'	No output yet
3	N/A	hello_gcs	Prints message: 'File image1.png uploaded.'	Message logged
4	N/A	hello_gcs	Function completes	Execution ends

💡 Function completes after processing the event triggered by file upload.

Status Tracker

Variable	Start	After Step 2	After Step 3	Final
event	{}	{'name': 'image1.png', 'bucket': 'photos'}	{'name': 'image1.png', 'bucket': 'photos'}	{'name': 'image1.png', 'bucket': 'photos'}
context	{}	context object	context object	context object

Key Moments - 3 Insights

Why does the function run automatically without being called explicitly?

Because the cloud platform detects the event (like a file upload) and triggers the function automatically, as shown in execution_table step 1.

What information does the function receive about the event?

The function receives event data like the file name and bucket, visible in execution_table step 2 and variable_tracker for 'event'.

Does the function run before or after the event happens?

The function runs after the event happens; the event triggers the function, as shown in concept_flow and execution_table step 1.

Visual Quiz - 3 Questions

Look at the execution_table, what is printed by the function at step 3?

A "Function starts"

B "File image1.png uploaded."

C "File uploaded to bucket 'photos'"

D "Execution ends"

💡 Hint

Check the 'Action' and 'Output' columns at step 3 in execution_table.

At which step does the function complete its execution?

A Step 4

B Step 3

C Step 2

D Step 1

💡 Hint

Look at the 'Action' column for 'Function completes' in execution_table.

If the event was a file deletion instead of upload, what would change in the execution_table?

A The function would not trigger at all.

B The function would print the same upload message.

C The event description in step 1 would change to file deletion.

D The function would complete earlier.

💡 Hint

Focus on the 'Event' column in execution_table step 1.

Concept Snapshot

Event triggered functions run automatically when a cloud event happens.
They receive event data and context as input.
The function executes its code and then finishes.
Common events: file upload, database change, message arrival.
No manual call needed; cloud detects and triggers.
Useful for automation and reacting to changes.

Full Transcript

Event triggered functions in cloud platforms run automatically when specific events occur, such as a file upload to storage. The cloud detects the event and triggers the function, passing event details like file name and bucket. The function executes its code, for example printing a message about the uploaded file, and then completes. This process requires no manual invocation, enabling automatic responses to cloud events.