Azure Functions Costs: The Hosting Plan Is the Bill
Stopping a function app rarely saves money. Changing the plan it runs on usually does.
Five hosting options, five billing models
Microsoft’s hosting options guide is the real pricing page for Functions, because the plan decides what you pay:
- Flex Consumption: billed on the number of executions, the memory of instances while they are actively executing, plus any always-ready instances you configure.
- Premium: billed on core seconds and memory across needed and prewarmed instances, and at least one instance per plan must always be kept warm.
- Dedicated (App Service plan): you pay the same as for any other App Service resource on that plan, whether or not the functions run.
- Container Apps: billed under Azure Container Apps plan types.
- Consumption (legacy): billed on executions, execution time and memory. Microsoft now labels it legacy and directs new serverless apps to Flex Consumption.
The pattern that wastes money is a function app that rarely runs, sitting on a Premium or Dedicated plan whose minimum footprint bills every hour.
Levers that follow from the plan
- Move low-traffic apps off Premium or Dedicated onto Flex Consumption, where idle time costs little beyond any always-ready instances.
- On Flex Consumption, keep always-ready instances only where cold start is a real problem.
- On a shared App Service plan, shrink or consolidate the plan itself; stopping one app on a plan that other apps still use does not reduce the plan’s charge.
What ZopNight finds
ZopNight can stop and start a function app on a schedule, but on a Premium or Dedicated plan the plan keeps billing, so a stopped app saves nothing until the plan changes; the directory’s Function App scheduling notes explain why. Change the plan instead.
The rules from the Azure catalog aim at the plan instead:
- Idle Azure Function App prices the full Premium or Dedicated plan cost as recoverable when the app shows no real activity, and abstains when the plan has no price rather than guessing.
- Azure Function Premium Plan with Low Executions proposes moving an underused Premium plan to consumption billing.
- Idle Azure App Service Plan and Azure App Service Plan Right-sizing handle the plan underneath; the right-sizing fix can run through the one-click resize workflow.
- Posture checks: Azure Function App Deprecated Runtime Version, Azure App Service SSL Not Enforced and Azure App Service Authentication Not Enabled.
An admin can open a Jira ticket from any finding, carrying the resource, the saving and the suggested fix, and the ticket status syncs back to the recommendation.
Fact sheets: Function Apps and App Service plans. Background: serverless cost management.