Invoke aws lambda from aws lambda in same vpc

Question

I premise I'm not a systemist nor network engineer. I'm trying to invoke a lambda function from another lambda function in the same vpc. My network configuration is:

1 vpc
1 public subnet and 1 private subnet
2 route tables
1 internet gateway
1 security group

My lambda:

is attached to both subnets and to sec group;
connects to db and retrieves data;
invokes lambda function to send push notification.

But when the first one tries to invoke the second aws returns timeout exception. My idea is that the first one "can't see" the second.

How can I solve the problem?

Thanks

Chris Williams · Accepted Answer · 2020-09-01 08:33:08Z

3

This is actually going to be as a result of the first Lambda (which is configured to use a VPC) has no outbound internet connectivity.

Ensure that you have either a NAT Gateway or a NAT instance that are attached to the route table(s) of the associated subnets.

If your function needs internet access, use network address translation (NAT). Connecting a function to a public subnet doesn't give it internet access or a public IP address.

You will need to remove the attachment to the public subnet as a Lambda cannot be assigned a public IP, therefore it cannot use an Internet Gateway.

edited Sep 1, 2020 at 8:33

answered Sep 1, 2020 at 8:25

Chris Williams

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9 Comments

Chris Williams Over a year ago

Yes it will be charged

Giamma Over a year ago

So the only free solution is to include the second lambda code in the first, right? Maybe with a function in a separate file

Chris Williams Over a year ago

So either have your Lambda not in a VPC (if it does not need to connect to VPC resources), or yes you would need to merge the code

Giamma Over a year ago

I think lambda needs VPC to connect to rds mysql

Giamma Over a year ago

I sincerly don't understand why two lambdas in the same vpc have to exit to internet and enter again in the vpc to call each other

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John Rotenstein · Accepted Answer · 2020-09-01 09:52:42Z

1

If the first Lambda function is invoked asynchronously, it can specify a Destination for sending an event at the completion of execution.

The destination can be another AWS Lambda function. This invocation is triggered by the AWS service and does not require Internet access from the first Lambda function (and is therefore cheaper than using a NAT Gateway).

See: Configuring destinations for asynchronous invocation

(I haven't tried it myself, but it should work!)

answered Sep 1, 2020 at 9:52

John Rotenstein

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