12 Lambda Cold Starts

title: Lambda Cold Starts for Serverless APIs weight: 22 date: 2026-06-28 lastmod: 2026-06-28 description: Understand and optimize Lambda cold starts in serverless APIs using provisioned concurrency, SnapStart, smaller deployment packages, and keeping dependencies warm. tags: [api-development, serverless]

Lambda cold starts occur when a new execution environment initializes, adding 100ms-5s latency for the first request, mitigated by provisioned concurrency, SnapStart (Java/Node.js), smaller deployment packages, and optimized dependency loading.

```python
import json
import time

# Cold start initialization (runs once per environment)
WARM_START = False
INIT_TIME = None

def initialize():
    global WARM_START, INIT_TIME
    if not WARM_START:
        INIT_TIME = time.time()
        # Heavy initialization: load ML models, database connections
        print(f"Cold start initialization at {INIT_TIME}")
        WARM_START = True

def lambda_handler(event, context):
    initialize()

    start = time.time()
    result = process_request(event)
    duration = time.time() - start

    print(f"Request processed in {duration*1000:.2f}ms")
    return api_response(200, {"result": result, "duration_ms": duration*1000})

What's Next

Now learn about Lambda VPC configuration in Building Serverless APIs.