Mastering APISIX Health Checks: Active and Passive Monitoring Strategies
Published: 2024-01-11 09:35:35

In the era of digitization, the availability and stability of services are crucial for the success of enterprises. As a key component of [microservices](https://api7.ai/blog/what-are-microservices) architecture, the API gateway plays a significant role. [APISIX](https://apisix.apache.org/), an open-source API gateway platform, ensures the continuity and stability of services through its health check mechanism.

When an upstream node faces faults or performance issues, APISIX promptly detects and responds. It dynamically reroutes traffic to other healthy upstream nodes based on health check results, ensuring timely and accurate processing of requests. This dynamic traffic control mechanism not only enhances system availability but also strengthens fault tolerance.

## Health Check Mechanism

APISIX's health check mechanism is divided into two types: active health check and passive health check.

![Active and Passive Health Check](https://static.apiseven.com/uploads/2024/01/11/ViK6sq4r_%E5%81%A5%E5%BA%B7%E6%A3%80%E6%9F%A5%20%281%29.png)

### Active Health Check

The active health check involves the API gateway proactively sending requests to check the status of backend services. With configured active health checks, APISIX periodically sends requests to upstream nodes, determining service health and availability based on their responses. This timely detection of unhealthy nodes prevents routing requests to nodes with suboptimal states. It's important to note that active health checks consume system resources and network bandwidth.

Imagine a helper constantly sending a "How are you?" signal to backend services. If the backend service responds within a specified time with "I'm good!", the helper considers the service healthy. If there is no response or the response indicates an issue, the helper may redirect traffic to other healthy services.

### Passive Health Check

The passive health check occurs when the API gateway receives requests from clients, it will simultaneously check the status of corresponding upstream service nodes. This method requires fewer resources as it only performs checks when requests are received. However, solely using passive health checks cannot re-mark unhealthy nodes as healthy, so it's typically used in conjunction with an active health check strategy.

In essence, with passive health checks enabled, when a request reaches APISIX, it checks if the corresponding service is healthy. If the service responds normally, APISIX understands that the service is in good condition.

## Practical Recommendations

**1. Combine Active and Passive Checks**:

   In scenarios with numerous nodes, configuring both active and passive health checks is recommended. Active checks serve for periodic status inspections, while passive checks monitor real-time responses. This combination facilitates prompt detection of node failures, preventing misjudgments due to traffic misrouting.

**2. Avoid Conflicting Configurations**:

   Ensure consistency in health check configurations. For instance, in active check mode, if HTTP 403 is considered a healthy response code, conflicting definitions in passive mode may lead to incorrect health assessments. Thus, it's crucial to avoid conflicting settings in configurations.

**3. Configure Timeout Reasonably**:

   The timeout parameter in active health checks is critical. Setting it too short may lead to misjudging healthy nodes, while setting it too long may cause delays in health check responses. It is advisable to configure timeouts based on actual application scenarios and node performance.

**4. Reasonable Health Check Interval**:

   The interval between health checks should be configured appropriately. Too short intervals may impose unnecessary system burdens, while too long intervals may result in delayed detection of node failures. It is recommended to configure health check intervals based on actual needs.

![Health Check Ensures High Availability](https://static.apiseven.com/uploads/2024/01/11/9vXvS7Oi_modern-equipped-computer-lab.jpg)

## Future Prospects

**1. Custom Health Check Logic**

   APISIX aims to provide more flexible custom health check mechanisms. Users might be able to write custom health check scripts or functions to implement specific health check logics, allowing for finer control based on actual requirements.

**2. Enhanced Anomaly Detection**

   Leveraging machine learning algorithms and big data analysis, APISIX seeks to enhance its anomaly detection capabilities. By learning from historical data, APISIX can automatically identify patterns of abnormal requests and changes in node states, enabling earlier detection of potential issues.

**3. Integration with Alert Mechanisms**

   To better meet the needs of business users, real-time health check feedback and alert mechanisms might be introduced. When node statuses change, instant notifications could be sent to relevant personnel for timely actions in problem resolution.

**4. Dynamic Adjustment of Health Check Policies**

   With changing business requirements, APISIX may offer the capability to dynamically adjust health check policies. For instance, based on node load and response time, parameters such as frequency and timeout for health checks could be dynamically adjusted to balance system resources and availability needs.

**5. Improved Integration with Microservices Architecture**

   As [microservices](https://api7.ai/solutions/monolith-to-microservices) architecture becomes more prevalent, APISIX aims to further optimize its health check mechanism for better integration. This could involve providing integration capabilities with container orchestration platforms like Kubernetes, achieving linkage with container health checks, and further enhancing service availability and stability.

## Conclusion

Health check helps enterprises promptly detect faults or abnormal situations in the system, avoiding service interruptions due to node failures. By continuously monitoring node statuses in real-time, the health check mechanism provides timely feedback for enterprises to take appropriate measures, enhancing system stability and availability.

The health check mechanism is a critical component of APISIX, helping enterprises build more reliable, efficient, and secure services. APISIX is expected to further optimize its health check mechanism in the future. This may involve integrating more monitoring tools, offering custom health check logic, enhancing anomaly detection capabilities, etc.

Through these optimization measures, APISIX aims to assist enterprises in improving the stability and availability of their systems, better meeting the needs of business users.