Implementing Zuul Logging Filter

In a microservice architecture, API Gateway is an important component, and Zuul is a popular open source API Gateway solution from Netflix. Implementing logging filters in Zuul is important to track the flow of requests and responses between different microservices.

Syntax

The following is the syntax for implementing a logging filter in Zuul:

public class LoggingFilter extends ZuulFilter {

    private Logger logger = LoggerFactory.getLogger(LoggingFilter.class);

    @Override
    public String filterType() {
        return "pre";
    }

    @Override
    public int filterOrder() {
        return 1;
    }

    @Override
    public boolean shouldFilter() {
        return true;
    }

    @Override
    public Object run() throws ZuulException {
        HttpServletRequest request = RequestContext.getCurrentContext().getRequest();
        logger.info("Request URI:{}", request.getRequestURI());
        return null;
    }
}

Example

Consider the following example where we create a logging filter in a Zuul gateway application:

public class ZuulGatewayApplication {

    public static void main(String[] args) {
        SpringApplication.run(ZuulGatewayApplication.class, args);
    }

    @Bean
    public LoggingFilter loggingFilter() {
        return new LoggingFilter();
    }
}

This creates a LoggingFilter bean which is then registered with the Zuul gateway. The LoggingFilter class extends the ZuulFilter class and overrides the necessary methods to implement the filter.

Output

When a request is made to the Zuul gateway, the LoggingFilter logs the request URI to the console:

INFO 1552 --- [nio-8765-exec-1] c.e.exercise.gateway.LoggingFilter       : Request URI:/api/payment/order/1234

Explanation

In the above example, the LoggingFilter extends the abstract ZuulFilter class, which provides a set of methods to implement the filter. The filterType() method returns the filter type as "pre", indicating that the filter is a pre-routing filter that is applied before the request is forwarded to the microservice.

The filterOrder() method specifies the order of execution of the filter. In this case, it is set to 1, meaning that it will be executed before any other filters that may be applied.

The shouldFilter() method returns true, indicating that the filter should be applied to all requests.

The run() method contains the logic of the filter. In this case, it extracts the request URI from the current context and logs it to the console using a logger.

Use

Logging filters in Zuul can be used to track the flow of requests and responses between different microservices. They can provide valuable insights into the performance and behavior of the microservices, and help identify issues or bottlenecks in the system.

Important Points

• Zuul filters provide an easy way to intercept and modify requests and responses in a microservice architecture.
• Logging filters can be used to track the flow of requests and responses between microservices and provide insights into the performance and behavior of the system.
• Filters can have different types, orders of execution, and execution conditions depending on the use case.

Summary

In this tutorial, we learnt how to implement a logging filter in a Zuul gateway application. We showed the syntax, explained the example, output and the various methods used to create the filter. We also discussed the use cases and important points related to Zuul filters.