[Microservice] Feign integrates Sentinel, and deeply explores Sentinel’s isolation and circuit breaker degradation rules, as well as authorization rules and custom exception return results.

Circuit breaker downgrade process:

The circuit breaker downgrade process is shown in the figure below:

The process description is as follows:

1. The circuit breaker is initially in the Closed state, allowing all requests to access the service.
2. When the number of failed service calls or the proportion of slow requests reaches the threshold, the circuit breaker enters the Open state, intercepting all requests and failing quickly.
3. After a period of time, the circuit breaker enters the Half-Open state, allowing some requests to access the service to test whether the service has returned to normal.
4. If a request in the Half-Open state succeeds, the circuit breaker enters the Closed state, allowing all requests to access the service.
5. If a request in the Half-Open state still fails, the circuit breaker continues to remain in the Open state until the next attempt to enter the Half-Open state.

Circuit breaker degradation is implemented through this state machine, which can help services avoid avalanche effects under abnormal circumstances and improve system availability and stability.

3.2 Circuit breaker strategy - slow call

There are three circuit breaker fusing strategies: slow call, abnormal ratio, and abnormal number.

Slow call means that when the service response time (RT) is greater than the specified time, the request is considered a slow call request. Within the specified time, if the number of requests exceeds the set minimum number and the slow call ratio is greater than the set threshold, the circuit breaker will be triggered.

For example, set a slow call degradation policy through the Sentinel console:

Description:
When the RT exceeds 500ms, it is a slow call. The requests in the last 10000ms are counted. If the number of requests exceeds 5 times and the slow call ratio is not less than 0.5, the circuit breaker is triggered and the circuit breaker duration is 5 seconds. Then enter the Half-open state and release a request for testing.

Now there is a requirement: to set degradation rules for the query user interface of UserClient. The RT threshold for slow calls is 50ms, the statistical time is 1 second, the minimum number of requests is 5, the failure threshold ratio is 0.4, and the circuit breaker Duration is 5:

In order to trigger the slow call rule, we need to modify the business in UserService to increase the business time:

@GetMapping("/{id}")
public User queryById(@PathVariable("id") Long id ) throws InterruptedException {<!-- -->
    if(id == 1){<!-- -->
        // Sleep, trigger slow call circuit breaker strategy
        Thread.sleep(60);
    }
    return userService.queryById(id);
}

After restarting the user-service service, we can trigger this circuit breaker mechanism by quickly refreshing the browser:

When the container is triggered, the interfaces serving other IDs will also be disconnected:

3.3 Circuit Breaker Strategy - Abnormal Ratio and Number of Abnormalities

The exception ratio or number of exceptions are statistics of calls within a specified period. If the number of calls exceeds the specified number of requests, and the proportion of exceptions reaches the set proportion threshold (or exceeds the specified number of exceptions), a circuit breaker is triggered.

This can also be set via the Sentinel console:

Description:

Count the requests in the last 1000ms. If the number of requests exceeds 10 times and the abnormality ratio is not less than 0.5, the circuit breaker will be triggered and the circuit breaker duration is 5 seconds. Then enter the Half-open state and release one request for testing.

The following is an example of abnormal proportions:

For example, there is a requirement now: to set a degradation rule for the query user interface of UserClient. The statistical time is 1 second, the minimum number of requests is 5, the failure threshold ratio is 0.4, and the circuit breaker duration is 5s:

In order to trigger exception statistics, you also need to modify the business in UserService and throw an exception:

@GetMapping("/{id}")
public User queryById(@PathVariable("id") Long id) throws InterruptedException {<!-- -->
    if(id == 1){<!-- -->
        // Sleep, trigger slow call circuit breaker strategy
        Thread.sleep(60);
    } else if (id == 2) {<!-- -->
        throw new RuntimeException("Demonstration triggers abnormal ratio fuse!");
    }
    return userService.queryById(id);
}

At this time, the user with access ID 2 will throw an exception.

After restarting the user-service service, we can trigger this circuit breaker mechanism by quickly refreshing the browser:

4. Authorization rules

4.1 What are authorization rules

Authorization rules are used to control the source of the caller, and are usually divided into two methods: whitelist and blacklist:

• Whitelist: Add the specified origin to the whitelist to allow these callers to access the service.
• Blacklist: Add the specified origin to the blacklist and do not allow these callers to access the service.

In the Sentinel console, you can configure authorization rules as follows:

Now, we can serve the order-service service from both the browser and the gateway:

If you now need to restrict only requests from the gateway to access the order-service service, then fill in the name of the gateway in the flow control application.

4.2 Example of authorization rules

The following will demonstrate how to use Sentinel's authorization rules to limit requests to the order-service service to only come from the gateway gateway.

Sentinel obtains the source of the request through the parseOrigin interface of the RequestOriginParser interface:

public interface RequestOriginParser {<!-- -->
// Get the origin from the request object, and customize the acquisition method
    String parseOrigin(HttpServletRequest request);
 }

RequestOriginParser is an interface provided by Sentinel for parsing the origin of the request. This interface defines a method parseOrigin. We need to implement this method to obtain the request source information from the request object in a custom way.

Therefore, we try to get a request header named origin from request as the value of origin to determine whether the request comes from the gateway. in accordance with. The steps to achieve this are as follows: