A Comprehensive Guide to Rate Limiting in the Age of APIs and Microservices

Impart Security
Published on
April 16, 2024
Read time
Impart Security
April 16, 2024

Rate limiting is a crucial security control that prevents excessive usage of APIs and services by clients. However, many people have an overly simplistic understanding of rate limiting, believing it to be just a fixed window over a single network interface. This viewpoint may work well with simple web applications, but falls short with microservices and APIs.

In this blog post, we'll dive deep into rate limiting, helping you expand your understanding of this critical security control. We'll also explore how APIs and microservices require a more comprehensive approach to rate limiting, and why relying on simple tools might not be enough. We'll discuss the various techniques of rate limiting, examine how they can be applied to different scenarios, and offer insights on how to find the right solution for your needs.

The Growing Importance of Rate Limiting in the Age of APIs and Microservices

APIs and microservices introduce new complexities to rate limiting due to their distributed nature and the enterprise environments they often operate in. The following points highlight the reasons for the increased importance of rate limiting in this context:

  • API scale is significantly more distributed and more complex than normal web scale. APIs often involve multiple components and services, which can result in a highly distributed architecture. This complexity requires a more sophisticated approach to rate limiting, ensuring consistent enforcement across all components.
  • APIs are typically deployed into heterogeneous and complex enterprise environments. In large organizations, APIs can be deployed across various platforms, load balancers, and data centers. Managing rate limiting in such complex environments can be challenging, requiring coordination and synchronization of rules and policies.
  • APIs have a more difficult-to-manage security posture than web applications. Due to their granularity and flexibility, APIs can be more susceptible to security vulnerabilities. Implementing comprehensive rate limiting is essential to protect APIs from various attacks and ensure their security.
  • Load balancing tools struggle to scale across multiple instances. Even load balancing tools can face issues when scaling across multiple instances, making it difficult to implement rate limiting effectively.

Rate Limiting: A Key Security Control in Application Security

Rate limiting plays a vital role in application security by mitigating the impact of Distributed Denial of Service (DDoS) attacks, ensuring fair resource allocation among users, and preventing excessive resource consumption. A robust rate limiting solution can help maintain a consistent quality of service for all users, protect critical resources, and safeguard applications from common application layer attacks:

  1. DoS attacks:  Denial of Service (DoS) attacks aim to overwhelm a target server or network by flooding it with a massive amount of requests, causing the system to become unresponsive or crash. Rate limiting helps mitigate DoS attacks by imposing a limit on the number of requests per IP address or client within a specified time window. This prevents an attacker from sending an excessive number of requests and consuming server resources. Additionally, rate limiting can be combined with IP blocking or blacklisting to ban IP addresses that consistently exceed the allowed request rate.
  2. Brute force attacks: Brute force attacks involve an attacker systematically attempting various combinations of usernames and passwords to gain unauthorized access to an account or system. Rate limiting can mitigate brute force attacks by limiting the number of authentication attempts per user or IP address within a specified time window. By doing so, it increases the time an attacker would need to exhaust all possible combinations, making the attack less feasible. Combining rate limiting with other security measures, such as account lockouts or multi-factor authentication, can further strengthen the protection against brute force attacks.
  3. Credential stuffing: Credential stuffing is an attack where an attacker uses previously leaked or stolen credentials (email addresses and passwords) to attempt unauthorized access to user accounts. Like brute force attacks, rate limiting can help mitigate credential stuffing attacks by limiting the number of authentication attempts per user or IP address within a specified time window. Additionally, rate limiting can be combined with other security measures, such as monitoring for unusual login patterns or implementing multi-factor authentication, to provide more robust protection against credential stuffing attacks.
  4. Scraping attacks: Web scraping involves extracting data from websites using automated tools, often without the website owner's permission. Scraping attacks can put significant strain on server resources and may lead to service degradation or data theft. Rate limiting can be used to mitigate scraping attacks by limiting the number of requests per client or IP address within a specified time window. This makes it more challenging for scrapers to extract large amounts of data quickly. Implementing rate limiting with user-agent or IP blocking, as well as using CAPTCHAs or other bot detection techniques, can further deter scraping attacks.

Rate Limiting in Distributed Systems

APIs require a more comprehensive rate limiting feature set than just throttling a single interface. While this might work in a traditional infrastructure setup, it doesn't work in the cloud or with microservices.

Consider the analogy of a toll booth: Rate limiting a single network interface is like managing the flow of cars through a single toll booth, which can become a bottleneck. In contrast, rate limiting a service with multiple network interfaces is like managing the flow of cars through multiple toll booths, requiring coordination of rate limiting rules across all interfaces.

Consistent rate limiting thresholds across multiple sets of infrastructure are crucial to defend against attacks such as application-level DDoS attacks, brute force login attempts, and scraping attacks that can target multiple components of an application or API.

Why Tools Based on ModSecurity May Not Be Enough

While tools like ModSecurity can provide basic rate limiting functionality, they may not offer the level of granularity, flexibility, and scalability required for modern APIs and microservices. Additionally, they may struggle to enforce consistent rate limits across distributed environments and multiple network interfaces, leaving APIs and services vulnerable to attacks.

Some limitations of simple tools like ModSecurity include:

  1. Limited support for different rate limiting techniques
  2. Difficulty in coordinating rate limiting across distributed environments
  3. Lack of scalability and performance in high-traffic scenarios
  4. Limited visibility and monitoring capabilities

Challenges with Rate Limiting in Heterogeneous Environments

Enforcing consistent rate limiting thresholds and counters across heterogeneous environments with different types of load balancers poses several challenges:

  1. Synchronization issues: In a distributed environment with multiple load balancers, ensuring that rate limiting counters are synchronized in real-time can be difficult. This may result in inaccurate rate limiting enforcement, allowing some clients to exceed the allowed request rate or blocking legitimate traffic.
  2. State management: Maintaining state across various load balancing technologies can be complex, as each technology may have its own mechanism for handling state. This may lead to inconsistencies in rate limiting policies and enforcement across different parts of the infrastructure.
  3. Scalability: As the number of load balancers and instances increases in a distributed environment, managing and scaling rate limiting policies and counters becomes more challenging. This may require additional resources, such as centralized data stores or distributed databases, to maintain state and ensure consistent enforcement.
  4. Operational complexity: Implementing rate limiting across multiple technologies and infrastructure components can introduce significant operational complexity. This may involve configuring and managing different load balancers, APIs, and data stores, as well as ensuring proper integration and communication between these components.
  5. Latency and performance: Enforcing rate limiting across various technologies and distributed environments can potentially impact performance and introduce latency. This may be due to the overhead of synchronizing counters, maintaining state, and coordinating policies across multiple components.

Embrace a Complete Rate Limiting Solution

Security engineers should not try to implement their own rate limiting solutions by piecing together multiple load balancers, distributed data stores, and policies. Instead, they should look for a comprehensive rate limiting solution that provides:

  1. Granularity and flexibility to handle complex API architectures and requirements
  2. Scalability to accommodate the growth of APIs and services
  3. Consistent enforcement of rate limiting rules across distributed environments and multiple network interfaces
  4. Ease of integration with existing tools and infrastructure
  5. Robust monitoring and reporting capabilities to help identify and address potential issues

By embracing a complete rate limiting solution, engineers can not only protect their APIs and services from various attacks but also ensure a consistent quality of service for all users. As APIs and microservices continue to play an increasingly important role in modern applications, it's essential to have a deep understanding of rate limiting and invest in a solution that offers the features and capabilities required to effectively manage and secure these critical resources. By moving beyond the overly simplistic view of rate limiting and embracing a complete solution, engineers can ensure their applications are secure, scalable, and provide a consistent quality of service for all users.

Evaluating Rate Limiting Solutions: Factors to Consider

When selecting a rate limiting solution, it's crucial to consider the following factors to ensure that you choose the right solution for your specific needs:

  1. Integration with your existing infrastructure: The rate limiting solution should be compatible with your existing infrastructure, such as load balancers, API gateways, and application servers, to minimize the need for extensive modifications.
  2. Ease of configuration and management: A good rate limiting solution should offer a user-friendly interface for configuring and managing rate limiting rules, policies, and thresholds. It should also provide comprehensive documentation and support for quick and efficient setup.
  3. Monitoring and reporting: The solution should offer robust monitoring and reporting capabilities, enabling you to track and analyze usage patterns, identify potential issues, and optimize rate limiting rules as needed.
  4. Flexibility and extensibility: A complete rate limiting solution should be flexible and extensible, allowing you to adapt and expand its functionality as your APIs and microservices grow and evolve.
  5. Cost and performance: It's essential to evaluate the cost and performance of the rate limiting solution, ensuring that it offers the necessary features and capabilities at a reasonable price without compromising performance.

By carefully evaluating these factors, you can find a rate limiting solution that meets your requirements and helps you effectively manage and secure your APIs and microservices.


In today's world of APIs and microservices, it's more important than ever for software engineers and security engineers to have a deep understanding of rate limiting concepts and techniques. By moving beyond the overly simplistic view of rate limiting and embracing a complete solution, you can effectively manage and secure your critical resources, ensuring a consistent quality of service for all users.

Don't leave your APIs and services exposed to unnecessary security risks. Invest in a comprehensive rate limiting solution that offers the features and capabilities required to effectively manage and secure these vital resources. In doing so, you'll be well-equipped to handle the challenges of modern application development and ensure the success of your projects.

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