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Inefficient Lambda Pricing Model for Steady High-Volume Workloads (Use Lambda Managed Instances)

The short version

A function has steady, high-volume traffic (or predictable load) but continues running on default Lambda pricing, where costs scale with execution duration.

Andrew Shieh

Principal Engineer / Director of Engineering, Operations @ SmugMug

AWS service
AWS Lambda
Category
Compute
Reference
CER-0296
Type
Suboptimal Pricing Model

Explanation

Why the waste happens and who it affects.

Lambda Managed Instances runs Lambda on EC2 capacity managed by Lambda and supports multi-concurrent invocations within the same execution environment, which can materially improve utilization for suitable workloads (often IO-heavy services). For these steady-state patterns, shifting from duration-based billing to instance-based billing (and potentially leveraging EC2 pricing options like Savings Plans or Reserved Instances) can reduce total cost - while keeping the Lambda programming model. Savings are workload-dependent and not guaranteed.

Billing model

The pricing dimensions that drive this cost.

Default Lambda charges per request and per-request execution duration. Lambda Managed Instances charges per request plus EC2 instance charges and a Lambda management fee, and does not charge separately per-request duration.

How to detect

4 checks to find it in your estate.

  • Review whether the function has sustained, predictable traffic rather than bursty "scale-to-zero" patterns
  • Assess whether paying for per-request duration is a dominant cost driver for the workload
  • Evaluate whether the workload can benefit from multi-concurrent processing (e.g., IO-heavy request handling)
  • Confirm the workload can tolerate a minimum always-on capacity model (i.e., it is not primarily cost-optimized by being idle most of the time)

How to fix

3 ways to remove the waste.

  • Consider Lambda Managed Instances for steady-state, predictable workloads where instance-based pricing and multi-concurrency can improve price-performance
  • Validate cost and operational fit by comparing expected instance-based spend (including management fee) versus current duration-based Lambda spend before broad adoption
  • Use default Lambda for bursty or sporadic workloads that benefit most from scale-to-zero economics

Documentation

Vendor references for pricing and configuration.

Browse the library

  • AWS LambdaCER-0124

    Overreliance on Lambda at Sustained Scale

    Lambda is designed for simplicity and elasticity, but its pricing model becomes expensive at scale. When a function runs frequently (e.g., millions of invocations per day) or for extended durations, the cumulative cost may exceed that of...

    Compute

  • AWS LambdaCER-0209

    Unnecessary Costs from Unused Lambda Versions with SnapStart

    Many teams publish new Lambda versions frequently (e.g., through CI/CD pipelines) but do not clean up old ones. When SnapStart is enabled on Python or .NET functions, each of these versions retains a cached snapshot, generating ongoing...

    Compute