Table of Contents

Introduction

The Azure Functions consumption plan is a serverless hosting option that automatically scales your application based on incoming event traffic. You pay only for the compute time you consume, making it a cost-effective solution for event-driven applications and workloads with variable or unpredictable traffic patterns.

This plan provides a fully managed environment where Azure handles all infrastructure concerns, allowing you to focus on writing code. It's ideal for scenarios such as:

  • Processing data from queues or topics
  • Responding to HTTP requests
  • Handling scheduled tasks
  • Integrating with other Azure services

How the Consumption Plan Works

When your Azure Function app is configured for the consumption plan, Azure monitors incoming events. When an event occurs, an instance of your function host is spun up to handle that event. If there are multiple concurrent events, Azure scales out by creating additional instances to process them in parallel. When there is no active traffic, the platform scales down to zero instances, meaning you are not charged for idle compute time.

Key characteristics:

  • Automatic Scaling: Azure automatically scales the number of function host instances based on the event load.
  • Pay-Per-Execution: You are billed based on the number of executions, execution time, and memory consumed.
  • Cold Starts: When a function has been idle for a period, the first request might experience a slight delay (a "cold start") as a new instance is initialized.
  • Resource Limits: The consumption plan has certain limits on execution duration and memory.

Note: To mitigate cold starts for latency-sensitive applications, consider the Premium plan or App Service plan which offer pre-warmed instances.

Pricing

The consumption plan pricing is based on two primary components:

  1. Number of Executions: Each time your function is triggered, it counts as one execution.
  2. Execution Time & Memory: This is measured in Gigabyte-seconds (GB-seconds). It's calculated by multiplying the memory allocated to your function by the time it runs.

Azure Functions offers a generous free grant each month, which often covers small to medium-sized applications entirely. Beyond the free grant, you pay for usage based on the defined rates.

For detailed and up-to-date pricing, please refer to the official Azure Functions pricing page.

Best Practices

To optimize your Azure Functions on the consumption plan:

  • Keep Functions Short-Lived: Design your functions to perform a single, specific task and complete quickly. Long-running operations can be broken down or handled by other services.
  • Manage Dependencies: Include only necessary dependencies to reduce cold start times.
  • Optimize Memory Usage: Choose an appropriate memory allocation. More memory isn't always better and increases cost.
  • Handle State Externally: Functions are stateless. Use external services like Azure Storage, Azure Cosmos DB, or Azure Cache for Redis to manage state.
  • Configure Triggers Wisely: Understand the behavior of different triggers and their potential impact on scaling and cost.

Monitoring Your Functions

Effective monitoring is crucial for understanding your function's performance, identifying issues, and managing costs. Azure Functions integrates with:

  • Application Insights: Provides deep insights into your function's performance, logs, dependencies, and exceptions.
  • Azure Monitor: Offers metrics and logs for an overview of your function app's health and resource utilization.

Key metrics to monitor include:

  • Function execution count
  • Execution duration
  • Memory usage
  • Errors and exceptions
  • HTTP status codes (for HTTP-triggered functions)

Common Triggers

Azure Functions can be triggered by a variety of events. Some of the most common triggers include:

  • HTTP Trigger: Invokes a function in response to an HTTP request.
  • Timer Trigger: Executes a function on a schedule defined by a cron expression.
  • Blob Trigger: Invokes a function when a new or updated blob is detected in Azure Blob Storage.
  • Queue Trigger: Invokes a function when a new message arrives in an Azure Queue.
  • Service Bus Trigger: Invokes a function based on messages arriving in an Azure Service Bus queue or topic.
  • Event Grid Trigger: Invokes a function in response to events published to Azure Event Grid.

Consumption Plan vs. Other Plans

Azure Functions offers several hosting plans, each with different characteristics:

Consumption Plan:

  • Pros: Cost-effective for variable workloads, automatic scaling, no infrastructure management.
  • Cons: Potential for cold starts, execution time limits, less control over the underlying environment.

Premium Plan:

  • Pros: Avoids cold starts with pre-warmed instances, longer execution times, VNet connectivity, more powerful hardware options.
  • Cons: Higher cost than consumption plan, less granular scaling than consumption.

App Service Plan:

  • Pros: Predictable costs, dedicated instances, no cold starts, full control over the environment, ideal for steady workloads.
  • Cons: Can be more expensive for low-utilization scenarios, requires manual scaling configuration.

The best plan depends on your specific application requirements, traffic patterns, and budget.