AWS Lambda Error -  RequestError: read ECONNRESET

#aws#lambda#devops#cloud

ECONNRESET occurs when Lambda’s network path is broken, unstable, or using stale connections

Problem

Your Lambda attempts to call an external service or an AWS API endpoint, but the connection abruptly drops. CloudWatch shows the error:

RequestError: read ECONNRESET

The function never receives a response — instead, the TCP connection is forcibly reset.

• Network path interrupted between Lambda and the destination
• VPC misconfiguration causing timeouts or dropped packets
• Connection reuse, keep-alive, or DNS caching issues inside the runtime

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Clarifying the Issue

read ECONNRESET means the remote end of the connection closed the socket unexpectedly. Lambda doesn’t generate this error — the network stack does. It can appear when accessing public APIs, AWS services, or internal endpoints.

• Happens frequently with VPC-enabled Lambdas lacking proper routing
• Can be triggered by slow endpoints exceeding Lambda’s TCP idle timeout
• Often appears during DNS changes, NAT exhaustion, or TLS mismatches

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Why It Matters

Connection resets cause intermittent failures that are difficult to detect in testing. Production workloads can silently degrade when large batches of requests start failing without clean error messages.

• Causes random request failures under load
• Breaks ingestion pipelines and upstream retries
• Hard to diagnose because logs show no server-side context

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Key Terms

• VPC ENI – Elastic Network Interface attached to Lambda for VPC access
• NAT Gateway – Network device enabling outbound internet for private Lambdas
• Idle timeout – Maximum time Lambda keeps TCP sockets open

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Steps at a Glance

1. Confirm the ECONNRESET error in CloudWatch logs
2. Determine whether the function runs inside a VPC
3. Test outbound connectivity from the runtime
4. Inspect NAT gateway, routing tables, and subnets
5. Validate DNS behavior and endpoint stability
6. Disable or reduce connection reuse where needed
7. Increase Lambda memory to boost network throughput
8. Re-test under load with controlled invocations

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Detailed Steps

Step 1: Confirm the ECONNRESET error in CloudWatch logs.

Start by pulling the most recent logs:

aws logs tail /aws/lambda/my-function --since 5m

You should see:

RequestError: read ECONNRESET

This confirms the reset occurred while reading from the remote endpoint.

Next, determine whether your Lambda is running in a VPC.

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Step 2: Determine whether the function runs inside a VPC.

Check the Lambda configuration:

aws lambda get-function-configuration \
  --function-name my-function \
  --query 'VpcConfig'

If you see subnets and security groups, you are inside a VPC.

If private subnets lack a NAT gateway, outbound traffic will fail with ECONNRESET or ETIMEDOUT.

Now validate connectivity.

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Step 3: Test outbound connectivity from the runtime.

Add a temporary test to your handler.

Node.js:

const https = require('https');
exports.handler = async () => {
  return new Promise(resolve => {
    https.get("https://example.com", res => resolve({ status: res.statusCode }));
  });
};

Python:

import requests
def handler(event, context):
    r = requests.get("https://example.com")
    return r.status_code

If this fails, your networking layer is broken — not your application code.

Move on to infrastructure checks.

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Step 4: Inspect NAT gateway, routing tables, and subnets.

For private Lambdas to reach the internet:

• Subnet must route 0.0.0.0/0 to a NAT gateway
• NAT must reside in a public subnet
• Public subnet must have a route to the Internet Gateway

Check route tables:

aws ec2 describe-route-tables \
  --filters Name=vpc-id,Values=vpc-123456

Incorrect routing is the number one cause of ECONNRESET inside VPC Lambdas.

Next, DNS.

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Step 5: Validate DNS behavior and endpoint stability.

Lambdas cache DNS aggressively. If an endpoint changes IPs or rotates behind a load balancer, the stale DNS entry can cause connection resets.

Check DNS:

aws lambda get-function-configuration \
  --function-name my-function \
  --query 'Runtime'

Newer runtimes handle DNS better; older ones may require forcing fresh lookups.

Also confirm the endpoint itself is stable.

Now address connection reuse.

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Step 6: Disable or reduce connection reuse where needed.

Node.js keeps sockets open by default; stale connections cause ECONNRESET.

Disable keep-alive.

Node.js:

const https = require('https');
const agent = new https.Agent({ keepAlive: false });

Python:

requests.get(url, headers=headers, timeout=5)

For high-volume workloads, use connection pools explicitly.

Next, increase Lambda resources.

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Step 7: Increase Lambda memory to boost network throughput.

Lambda’s network bandwidth scales with memory.

aws lambda update-function-configuration \
  --function-name my-function \
  --memory-size 1024

Higher memory reduces cold start time and increases network stability.

Finally, test under load.

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Step 8: Re-test under load with controlled invocations.

aws lambda invoke \
  --function-name my-function \
  --payload '{}' \
  out.json

Run several invocations quickly to see if errors disappear when routing and DNS issues are corrected.

If ECONNRESET persists, the remote service may be closing idle connections prematurely — add retries and shorter timeouts.

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Pro Tips

• NAT gateway in the wrong subnet causes intermittent resets
• Reuse connections carefully; stale sockets are a major failure point
• API endpoints that rotate IPs frequently require fresh DNS lookups

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Conclusion

ECONNRESET occurs when Lambda’s network path is broken, unstable, or using stale connections. By checking VPC routing, NAT configuration, DNS behavior, and connection reuse, you can eliminate connection resets and restore stable outbound traffic.

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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.