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.

Practice

1. What is a cold start in cloud services?

easy

A. The process of scaling up instances during high traffic

B. The delay when a service starts fresh after being idle

C. A security check before allowing user access

D. The automatic backup of data in the cloud

Solution

1. Step 1: Understand the term 'cold start'

   A cold start refers to the initial delay experienced when a cloud service starts fresh, usually after being idle or after a new deployment.

2. Step 2: Compare options to definition

   Only The delay when a service starts fresh after being idle describes this delay. Other options describe scaling, security, or backup, which are unrelated.

3. Final Answer:

   The delay when a service starts fresh after being idle -> Option B

4. Quick Check:

   Cold start = initial delay after idle [OK]

Hint: Cold start means waiting for service to start fresh [OK]

Common Mistakes:

• Confusing cold start with scaling
• Thinking cold start is a security feature
• Mixing cold start with backup processes

2. Which of the following is the correct way to reduce cold start time in a serverless function on GCP?

easy

A. Use a larger instance type for the function

B. Increase the memory allocation to zero

C. Disable all logging to speed up startup

D. Keep the function code minimal and dependencies small

Solution

1. Step 1: Identify factors affecting cold start

   Cold start time depends on how much code and dependencies need loading. Smaller code and fewer dependencies reduce startup time.

2. Step 2: Evaluate options

   Keep the function code minimal and dependencies small correctly suggests minimizing code and dependencies. Increase the memory allocation to zero is invalid (memory can't be zero). Disable all logging to speed up startup disables logging but doesn't affect cold start much. Use a larger instance type for the function is irrelevant for serverless functions.

3. Final Answer:

   Keep the function code minimal and dependencies small -> Option D

4. Quick Check:

   Smaller code = faster cold start [OK]

Hint: Smaller code and dependencies reduce cold start [OK]

Common Mistakes:

• Setting memory to zero (invalid)
• Thinking logging affects cold start significantly
• Choosing instance size for serverless functions

3. Consider this simplified serverless function behavior:

1. Function is idle for 30 minutes.
2. A request arrives.
3. Function starts fresh (cold start).
4. Subsequent requests arrive quickly.
What happens to the response time for the first and second requests?

medium

A. First request slow, second request fast

B. Both requests slow

C. Both requests fast

D. First request fast, second request slow

Solution

1. Step 1: Understand cold start impact on first request

   The first request after idle triggers a cold start, causing delay and slower response.

2. Step 2: Understand warm start for subsequent requests

   After the function is running, subsequent requests use the warm instance, so response is fast.

3. Final Answer:

   First request slow, second request fast -> Option A

4. Quick Check:

   Cold start delays first request only [OK]

Hint: First request cold, next requests warm and fast [OK]

Common Mistakes:

• Assuming all requests are slow
• Thinking cold start affects every request
• Confusing cold start with scaling delays

4. You deployed a new version of a Cloud Function, but users report slow responses initially. What is the most likely cause?

medium

A. Insufficient user permissions

B. Network outage in the region

C. Cold start due to new deployment

D. Function code has syntax errors

Solution

1. Step 1: Analyze symptoms after deployment

   New deployments cause cold starts because the function must start fresh with new code.

2. Step 2: Rule out other options

   Network outages cause broader failures, syntax errors cause function failures, and permissions cause access errors, not initial slowness.

3. Final Answer:

   Cold start due to new deployment -> Option C

4. Quick Check:

   New deploy = cold start delay [OK]

Hint: New deployment triggers cold start delay [OK]

Common Mistakes:

• Blaming network issues without evidence
• Assuming syntax errors cause slow start
• Confusing permissions with performance

5. You want to minimize cold start delays for a Cloud Run service that experiences unpredictable traffic spikes. Which strategy is best?

hard

A. Configure minimum instances to keep some containers always warm

B. Set maximum instances to 1 to limit scaling

C. Disable autoscaling to avoid cold starts

D. Use a larger container image to speed startup

Solution

1. Step 1: Understand cold start mitigation in Cloud Run

   Setting minimum instances keeps some containers running, avoiding cold starts during traffic spikes.

2. Step 2: Evaluate other options

   Set maximum instances to 1 to limit scaling limits scaling and can cause delays. Disable autoscaling to avoid cold starts disables autoscaling, harming performance. Use a larger container image to speed startup increases image size, worsening cold start.

3. Final Answer:

   Configure minimum instances to keep some containers always warm -> Option A

4. Quick Check:

   Minimum instances reduce cold start [OK]

Hint: Keep minimum instances running to avoid cold start [OK]

Common Mistakes:

• Limiting max instances causing bottlenecks
• Disabling autoscaling hurting responsiveness
• Using larger images increasing cold start time