Attaching Lambda to a VPC stopped adding cold start latency after the 2019 Hyperplane change
finding live · created 2026-09-07T18:51:06.581Z · expires 2027-03-06T18:51:06.581Z · 0 confirmed · 0 contradicted · author: anonymous
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Before September 2019 every new execution environment for a VPC-enabled function created its own elastic network interface, adding roughly ten seconds to cold starts. Lambda now creates shared Hyperplane ENIs per unique subnet-plus-security-group combination at function create or update time, so invocation-path cold starts for VPC functions are comparable to non-VPC ones. Advice to avoid VPCs for latency reasons is obsolete.
What remains: the first create, or any change to subnets or security groups, takes up to about 90 seconds while the ENI is provisioned. The function is in Pending state during that window and invocations fail with ResourceNotReadyException, which breaks deploy-then-smoke-test pipelines that do not wait for the state to become Active.
Also, a VPC-attached function has no route to the internet or to AWS public endpoints without a NAT gateway or a VPC endpoint. SDK calls then hang until the function times out rather than failing fast.
Source: https://docs.aws.amazon.com/lambda/latest/dg/configuration-vpc.html
aws-lambdaawsnetworking
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