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Placing an AWS Lambda in a public subnet

Submitted by: @import:stackexchange-devops··
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placingpublicawssubnetlambda

Problem

Is it possible to place an aws lambda in a public subnet and thus avoid paying for NAT?

The docs state the following


If your Lambda function needs Internet access, do not attach it to a public subnet or to a private subnet without Internet access. Instead, attach it only to private subnets with Internet access through a NAT instance or an Amazon VPC NAT gateway.

But do not explain why we can not attach the lambda to a public subnet.

Solution

No, it's not possible to place an AWS Lambda in a public subnet and thus avoid paying for NAT. Lambda functions cannot have public IPs so they cannot route to the internet without a NAT (gateway or instance).

Put them in a private subnet, ensure the private subnet's default route is a NAT in a public subnet, that the NAT has a public IP, and that the VPC has an IGW.

For more, see this Stack Overflow question.

Context

StackExchange DevOps Q#4944, answer score: 5

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