AWS Lambda Error: Task timed out after X seconds

#aws#lambda#devops#cloud

This error occurs when your function exceeds its allowed execution time.

Problem

Your Lambda function fails with an error like:

Task timed out after 6.00 seconds

Lambda forcibly stopped your function because it did not finish before the configured timeout.

Clarifying the Issue

This error means one of two things:

1. The function genuinely needs more time than its configured timeout.
2. The function is stuck in initialization or blocked inside an external call.

Lambda enforces the timeout strictly — it does not wait beyond the configured limit.

Why It Matters

Timeouts are one of the most common AWS Lambda failures. They appear in workflows involving:

• External APIs
• Private VPC subnets
• DynamoDB or RDS
• S3 operations
• Heavy imports or initialization
• Large cold-start footprints

Timeouts cause:

• Partial writes
• Broken workflows
• Retry storms
• Higher costs
• Latency spikes

A reliable diagnosis is critical for stability.

Key Terms

• Timeout: Maximum allowed time for Lambda to run.
• Initialization Phase: The time Lambda spends loading your code before calling the handler.
• Handler Phase: The execution of your business logic.
• VPC Cold Start: Delay from attaching ENIs in private subnets.

Steps at a Glance

1. Identify how long the function actually runs before the timeout.
2. Determine whether the delay is during initialization or inside the handler.
3. Review all external calls for slow or blocked behavior.
4. Increase the timeout if appropriate.
5. Optimize slow code paths or dependency bottlenecks.
6. Test again and confirm the timeout is resolved.

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Step 1: Identify how long the function actually runs

Open CloudWatch Logs and find the REPORT line:

REPORT RequestId: abc Duration: 5985.34 ms Billed Duration: 6000 ms
Task timed out after 6.00 seconds

If Duration is close to the timeout, your function simply needs more time.

If Duration is tiny (e.g., 5–20 ms), your function may be stuck before it can log anything — usually initialization or networking.

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Step 2: Determine whether the delay is in initialization or the handler

If your handler logs never appear, the issue is often in initialization:

• Large imports
• Heavy libraries
• VPC cold start
• Connecting to RDS or third-party services
• Loading models or binaries

Add a marker inside your file but outside the handler:

print("Lambda initialization complete")

If this line never appears, the delay is occurring before the handler starts.

Additional diagnostic tip:
Check the CloudWatch REPORT line for Init Duration or Max Init Duration. If these values are high, the timeout is occurring during Lambda initialization — not inside your handler.

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Step 3: Review all external calls

Timeouts commonly occur due to slow external dependencies.

Add timing logs:

import time
start = time.time()
# external call here
print(f"External call took {time.time() - start} seconds")

Check:

• Third-party HTTP APIs
• DynamoDB reads/writes
• RDS connections
• S3 operations
• Secrets Manager or SSM Parameter Store

These often cause silent, hidden delays.

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Step 4: Increase the Lambda timeout if appropriate

If the workload is valid but just needs more time:

aws lambda update-function-configuration \
  --function-name MyFunction \
  --timeout 30

Expected output:

{
  "FunctionName": "MyFunction",
  "Timeout": 30
}

Adjust according to the real runtime. Avoid overly large values.

---

Step 5: Optimize slow code or dependency paths

Reduce overhead where possible:

• Use async HTTP clients
• Replace DynamoDB scans with queries
• Reuse database connections
• Minimize imports
• Precompute reusable values
• Move long-running work to Step Functions
• Offload compute-heavy work to ECS/Fargate

Even small improvements significantly reduce runtime.

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Step 6: Test the function and confirm completion

Invoke the function:

aws lambda invoke \
  --function-name MyFunction \
  response.json
cat response.json

If successful, you’ll see normal handler output.

If it still times out, compare:

• CloudWatch Duration
• Timeout limit
• External call timings

This will show exactly where the bottleneck remains.

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Pro Tips

• If your function always times out at the full limit (for example, exactly 30 seconds) with no logs from the external call, this often indicates VPC egress blockage — the Lambda cannot reach the internet or the target endpoint due to missing NAT or routing.
• VPC cold starts can add 2–10 seconds of delay. Avoid VPC unless required.
• If calling third-party APIs, set your own request timeout lower than the Lambda timeout to avoid hanging.
• Provisioned Concurrency reduces cold starts and improves predictability.
• Break long-running work into smaller steps using Step Functions.

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Conclusion

This error occurs when your function exceeds its allowed execution time. By identifying whether the delay is in initialization, handler logic, or external calls — and by tuning timeouts or optimizing slow code paths — you restore reliable execution. Once the bottleneck is identified and resolved, Lambda becomes stable and predictable again.

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Aaron Rose is a software engineer and technology writer at tech-reader.blog and the author of Think Like a Genius.