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A Step-by-Step Guide to Throttling and Quotas in AWS API Gateway

Amazon API Gateway

As businesses increasingly rely on APIs to expose their services, managing API access becomes crucial to ensure reliability, security, and a smooth user experience. AWS API Gateway is a fully managed service that makes it easy for developers to create, publish, maintain, monitor, and secure APIs at any scale. APIs act as the "front door" for applications to access data, business logic, or functionality from your backend services. Using API Gateway, you can create RESTful APIs and WebSocket APIs that enable real-time two-way communication applications. API Gateway supports containerized and serverless workloads, as well as web applications. AWS API Gateway provides robust tools to implement throttling and quotas, which are essential for controlling traffic, preventing abuse, and maintaining service quality. This blog post will delve into the best practices for setting up and managing throttling and quotas in AWS API Gateway.

AWS API Gateway

Understanding Throttling and Quotas 

Throttling is the process of limiting the number of API requests a client can make in a given period. Throttling helps maintain the performance of calling applications during unexpected spikes in API calls. Spikes can happen when many users use an application at the same time. It helps to prevent overloading the backend systems and ensures fair usage among multiple clients. 


 

Quotas specify the maximum number of requests a client can make over a longer period, such as a day or a month. API quotas usually describe a certain number of allotted calls for longer intervals. You can also limit API calls that consume more backend computing power and impact service. They help in enforcing usage limits and monitoring client usage patterns. 

Best Practices for Implementing Throttling 

1. Define Usage Plans: Usage plans in AWS API Gateway allow you to configure throttling limits and quotas for your APIs. You can configure a rate limit for specified clients that limits the number of messages they can send. If a client exceeds their allotted number of requests, their connection is throttled. Processing slows down, but the connection remains open to reduce errors. 

 

Each usage plan can be associated with one or more API stages. This allows you to control access to different versions of your API, such as development, staging, and production environments. By defining usage plans, you can ensure that your API remains performant and reliable, even under heavy traffic.

AWS API Gateway Throttling

2. Set Appropriate Rate and Burst Limits: Define rate limits (requests per second) and burst limits (maximum number of requests in a short time) based on your backend’s capacity and expected traffic patterns. Ensure these limits are aligned with your infrastructure's ability to handle load spikes. 

 

The number of API calls your backend can process per time unit is typically measured by TPS, or transaction per second. In some cases, systems also have a physical limit of data transferred in Bytes. Let’s say your backend can process 2,000 TPS — what’s known as backend rate limiting. With API Gateway rate limiting or API throttling, you can cap the number of requests an API gateway can process in a given period. Doing so protects backend services from being flooded with excessive messages.

 

When your system has the capacity or is idle, you may want to let a single client send more requests than the defined limit. An API burst temporarily accommodates this higher volume of requests while avoiding the potential for overload. If you have a configured rate limit of 500 TPS, that’s one request per 2 milliseconds (the burst zone). If your burst size is 0, and 2 requests are made in that 2-millisecond zone, one request will be processed and the other rejected. The key to API burst is balancing client demand with rate-limiting measures. That way, you can support surges in traffic without hindering API performance.

API Gateway rate limiting

3. Use API keys in Amazon API Gateway: Assign API keys to your clients and associate these keys with usage plans. This enables you to track and control each client's usage individually, enforcing usage plans and quotas effectively. 

 

These are the steps to use API keys:

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    1. Generate API Keys: Create unique API keys for each client using the AWS Management Console or API.

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    2. Assign API Keys to Usage Plans: Associate each API key with a usage plan to enforce specific rate limits and quotas.

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    3. Implement Key Validation: Configure your API Gateway to validate API keys on each request, ensuring that only authorized clients can access your services.


 

Using API keys in Amazon API Gateway helps you monitor and control API usage, providing insights into client behavior and preventing unauthorized access. 

AWS API Gateway Usage Plans And API Keys

4. Leverage Stage Variables: Use stage variables to manage different throttling settings across development, staging, and production environments without modifying the API configuration. 

 

These are the benefits of stage variables:

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   1. Environment-Specific Settings: Define variables for each stage (e.g., dev, test, prod) to manage different configurations, such as database endpoints or feature toggles.

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   2. Simplified Deployment: Deploy the same API configuration across multiple stages, using stage variables to customize behavior as needed.

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   3. Enhanced Debugging: Use stage variables to enable or disable logging and monitoring settings, helping you diagnose issues more effectively.


 

by leveraging stage variables, you can streamline your deployment process and maintain consistency across various environments. 

Best Practices for Implementing Quotas 

1. Monitor Usage: Tracking usage metrics is a critical part of API management. Usage metrics include data such as requests per second, request volume, latency, and throughput. Regularly monitor API usage to ensure that clients do not exceed their quotas. 

 

AWS users can monitor the API calls on a metrics dashboard in AWS API Gateway. They also can retrieve error, access, and debug logs from AWS CloudWatch. CloudWatch provides detailed metrics on API Gateway usage, helping you keep track of API performance and client activity. 

AWS API Gateway Quotas

2. Automate Alerts: Automating alerts is crucial for proactive API management. Set up CloudWatch alarms to notify you when a client approaches their quota limit or when API performance metrics deviate from expected thresholds. This allows you to take proactive measures, such as increasing the quota or notifying the client. 

 

To automate alerts, you have to define metrics first, such as request count, error rates, and latency. Second, you have to establish thresholds for these metrics to trigger alarms. For example, you might set an alarm to trigger when a client uses 90% of their monthly quota. Lastly, it is better to use SNS (Simple Notification Service) to send notifications via email, SMS, or other channels when alarms are triggered.

 

Automating alerts helps you stay ahead of potential issues, ensuring that you can address them before they impact your users. 

3. Graceful Degradation: Implement mechanisms in your backend to handle requests gracefully when clients exceed their quota limits. This might include returning informative error messages or temporarily reducing service quality instead of outright denying access. 

 

Here are some techniques for graceful degradation:

 

    1. Return Informative Error Messages: Instead of a generic error, return detailed messages explaining that the quota has been exceeded and suggest possible actions.

 

    2. Limit Features: Reduce the functionality available to clients who exceed their quotas. For instance, you might limit the frequency of certain operations or disabled non-critical features.

 

    3. Queue Requests: Implement queuing mechanisms to delay excess requests instead of rejecting them outright. This can help manage load spikes without causing abrupt disruptions.


 

Graceful degradation ensures a more seamless user experience, maintaining trust and reliability even under constrained conditions.

AWS API Gateway Graceful Degradation

Ensuring a Smooth User Experience

1. Transparent Communication: Clearly communicate throttling and quota limits to your clients. Provide detailed documentation and real-time access to their usage statistics via a developer portal or API so they can access documentation that helps them better understand the API’s value and how to test and use it. SLAs are often also attached to define service response times and availability.

2. Progressive Limits: Looking at API quota in more detail, you can imagine setting limits not only based on a client/consumer but also on a per-consumption application level. This is known as an application quota. Start with generous limits during the initial phase of your API’s lifecycle and gradually tighten them as you gain more insight into usage patterns and client behavior. 

3. Client-Side Rate Limiting: To enforce an API quota, you need to identify the client or consumer. That’s why we use the term user quota. Through an API marketplace that supports full lifecycle API management, consumers can easily select the subscription plan that suits their quota needs. Encourage clients to implement rate limiting on their side to prevent sudden spikes in request rates. This helps in distributing the load more evenly and avoids triggering throttling mechanisms unnecessarily. 

API Lifecycle

Conclusion

Implementing throttling and quotas in AWS API Gateway is essential for managing API access, preventing abuse, and ensuring a consistent user experience. By following these best practices, you can effectively control traffic, protect your backend services, and maintain high service quality. Regular monitoring and proactive adjustments will help you stay ahead of potential issues and provide a reliable API service to your clients. 

 

By thoughtfully setting up and managing throttling and quotas, you can create a scalable, resilient, and user-friendly API environment that benefits both your clients and your backend systems.

About The Author

Pouya Nourizadeh
AWS Enterprise Solutions Architect
Founder, Bringdev

AWS CloudWatch - Author
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