Explanation
Why the waste happens and who it affects.
However, these decisions are rarely revisited - even as usage patterns change.
In practice, many workloads running on Premium or App Service Plans have low invocation frequency, minimal execution time, and no strict latency requirements. This leads to consistent spend on compute capacity that is largely idle. Because these plans still "work" and don't cause reliability issues, the inefficiency is easy to overlook. Over time, this misalignment between hosting tier and actual usage creates significant invisible waste.
Billing model
The pricing dimensions that drive this cost.
Azure Functions are billed differently depending on the hosting plan selected. The Premium plan bills for core seconds and memory across needed and prewarmed instances, with at least one instance always kept warm. A Dedicated (App Service) plan bills for its provisioned instances whether or not functions run. The Flex Consumption plan bills for executions and for instance memory while functions are actively executing, plus any always-ready instances, and the legacy Consumption plan bills for executions, execution time, and memory used.
How to detect
6 checks to find it in your estate.
- Identify Function Apps running on Premium or App Service Plans
- Review invocation frequency and execution time to assess activity level
- Compare provisioned capacity (instances, memory) against actual usage patterns
- Check whether cold start latency is still a relevant concern for each workload
- Evaluate whether functions require features that Flex Consumption does not offer, such as Windows hosting, custom containers, or deployment slots
- Flag workloads with minimal activity that may not justify fixed-instance billing
How to fix
5 ways to remove the waste.
- Move low-usage or non-critical Function Apps to the Flex Consumption plan, which supports virtual network integration and optional always-ready instances; use the legacy Consumption plan only where Windows is required
- Pilot plan downgrades in non-production or latency-tolerant environments
- Use cost modeling tools to estimate savings from switching to the Flex Consumption plan
- Establish a review process to re-evaluate plan fit periodically, checking changes in invocation frequency, execution duration, latency needs, VNET requirements, and cost vs: usage.
- Document latency and feature requirements per workload to avoid defaulting to oversized plans
Documentation
Vendor references for pricing and configuration.