DynamoDB causing Lambda timeout

Question

I am experiencing an issue where Lambda functions occasionally time out without any error message other than a notification that the function timed out.

In order to find the root of the issue, I added logging at various points throughout my function and determined that everything functions properly until the first getItem() request to read data from DynamoDB. The read seems to be taking more than the 3.00 second timeout.

Naturally, I checked my DynamoDB table to see if there were any throttled reads or errors. DynamoDB's metrics show no throttles or errors, and read times remain in the double-digit milliseconds at most.

Clearly something is going wrong or getting dropped along the way. How can I fix this issue or at least catch it and retry the read?

This is a read-oriented function for a web API, so response times are critical. Hence, an increased timeout will not solve the issue.

dynamodb.getItem({
  "TableName": "tablename",
  "Key": { "keyname": { "S": "keyvalue" } },
  "AttributesToGet": [ "attributeA", "attributeB" ]
}, function(err, data) {
  if(err){
    context.done(err);
  } else {
    if("Item" in data){
      nextFunction(event, context);
    } else {
      context.done("Invalid key");
    }
  }
});

Solution 1

After significantly increasing the timeout, I found that a network error is eventually thrown:

{
    "errorMessage": "write EPROTO",
    "errorType": "NetworkingError",
    "stackTrace": [
        "Object.exports._errnoException (util.js:870:11)",
        "exports._exceptionWithHostPort (util.js:893:20)",
        "WriteWrap.afterWrite (net.js:763:14)"
    ]
}

This issue appears to be caused by an issue between Node.js and OpenSSL according to this thread. It sounds like the issue affects Node.js 4.x and up but not 0.10. This means you can either resolve the issue by downgrading the Lambda runtime to Node.js 0.10 or adding the following code when using aws-sdk:

new AWS.DynamoDB({
  httpOptions: {
    agent: new https.Agent({
      rejectUnauthorized: true,
      secureProtocol: "TLSv1_method",
      ciphers: "ALL"
    })
  }
});

Solution 2

Ran into a random lambda timeout issues while "put"ting data from lambda to DynamoDB. Lambda resides in a VPC (per organization policy).

Issue: Some (random) lambda containers would consistently fail while putting data and times out (set to 30 sec), while other containers got done putting data in a few milliseconds.

Root cause: There were two subnets (as suggested by AWS) configured. One was a private subnet and other was a public subnet. When a new lambda container is spun-off, it would randomly select one of the subnets. If it choose public subnet, it would consistently fail. If it choose private subnet, it would be done in a few milliseconds.

Solution: Remove public subnet and, rather, have two private subnets configured.

Solution 3

If your are launching your Lambda in VPC, try to launched in a Private Subnet instead of Public Subnet. I had the same problem and launching Lambda in a Private Subnet worked for me.

Comments

[Tyler]

Did you try using TLS v1?

[xtra]

What causes it to fail in the public subnet and succeed in the private subnet? What is the reason that the lambda function has to be in the private subnet?

[SystemDLL]

Lambda function is in a VPC, as it accesses an Aurora RDS. For more information on how to access internet (DynamoDB endpoint in this case) from a lambda in VPC, please refer to aws.amazon.com/premiumsupport/knowledge-center/…

[jayair]

The tricky thing here is that to be able to debug these issues you need to let the DynamoDB call fail. If used within a Lambda, make sure the call fails before the Lambda (or API Gateway) times out. We wrote about it in detail here - seed.run/blog/…

[gmanolache]

I had the same issue, because I didn't have a NAT gateway setup on the private subnets, the Lambda was not able to call the dynamo API.

[Jakub Bielan]

Thanks, increasing the timeout was a the crucial remark for me.

[Bracken]

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