Cold start behavior in GCP - Step-by-Step Execution

Process Flow - Cold start behavior

Request arrives

↓

Check if instance is running

Yes / No↓

Process request

↓

Send response

↓

Send response

When a request comes, the system checks if a running instance exists. If yes, it uses it immediately. If no, it starts a new instance, initializes it, then processes the request.

Execution Sample

GCP

1. Request received
2. Check running instance
3. If none, start instance
4. Initialize environment
5. Process request
6. Send response

This sequence shows how a cloud function handles a request, either using an existing instance or starting a new one causing a cold start delay.

Process Table

Step	Action	Instance State	Delay	Result
1	Request received	No instance running	N/A	Trigger check
2	Check running instance	No instance running	N/A	Decide to start new instance
3	Start new instance	Starting instance	High (cold start)	Instance initializing
4	Initialize environment	Instance initializing	High (cold start)	Environment ready
5	Process request	Instance ready	Low	Request processed
6	Send response	Instance ready	Low	Response sent
7	Next request received	Instance ready	Low (warm start)	Request processed immediately

💡 Execution stops after response is sent; subsequent requests may avoid cold start if instance remains active.

Status Tracker

Variable	Start	After Step 3	After Step 4	After Step 5	After Step 7
Instance State	No instance	Starting	Initialized	Ready	Ready
Delay	N/A	High	High	Low	Low
Request Processed	No	No	No	Yes	Yes

Key Moments - 3 Insights

Why does the first request take longer to process?

Because no instance is running initially (see execution_table step 2), the system must start and initialize a new instance causing a cold start delay.

What happens to the delay for subsequent requests?

After the instance is ready (step 5), subsequent requests use the warm instance, so delay is low (step 7).

Does the instance stay running forever?

No, instances may shut down after inactivity, causing future requests to trigger cold starts again.

Visual Quiz - 3 Questions

Look at the execution_table, what is the instance state at step 4?

A No instance running

B Starting instance

C Instance initializing

D Instance ready

💡 Hint

Check the 'Instance State' column at step 4 in the execution_table.

At which step does the cold start delay end?

A Step 5

B Step 4

C Step 3

D Step 7

💡 Hint

Look at the 'Delay' column; cold start delay is high until the environment is ready.

If the instance stays active, what delay is expected for the next request at step 7?

A Medium delay

B Low delay

C High delay

D No delay

💡 Hint

Refer to the 'Delay' column at step 7 in the execution_table.

Concept Snapshot

Cold start happens when no running instance exists.
System must start and initialize a new instance.
This causes higher delay for the first request.
Subsequent requests use warm instances with low delay.
Instances may shut down after inactivity, causing future cold starts.

Full Transcript

Cold start behavior in cloud functions means when a request arrives, the system checks if an instance is running. If none is running, it starts a new instance and initializes it, causing a delay called cold start. Once ready, the request is processed and response sent. Subsequent requests use the warm instance, so they are faster. Instances may shut down after inactivity, so cold starts can happen again later.