Spring 启动微服务 - 依赖

Question

There are two microservices deployed with docker compose. A dependecy between services is defined in docker compose file by depends_on property. Is it possible to achieve the same effect implicitly, inside the spring boot application?

Let's say the microservice 1 depends on microservice 2. Which means, microsearvice 1 doesn't boot up before microservice 2 is healthy or registered on Eureka server.

Answer 1

By doing some research, I found a solution to the problem.

Spring Retry resolves dependency on Spring Cloud Config Server. Maven dependency spring-retry should be added into the pom.xml, and the properties below into the.properties file:

spring.cloud.config.fail-fast=true
spring.cloud.config.retry.max-interval=2000
spring.cloud.config.retry.max-attempts=10

The following configuration class is used to resolve dependency on other microservices.

@Configuration
@ConfigurationProperties(prefix = "depends-on")
@Data
@Log
public class DependsOnConfig {

    private List<String> services;
    private Integer periodMs = 2000;
    private Integer maxAttempts = 20;

    @Autowired
    private EurekaClient eurekaClient;

    @Bean
    public void dependentServicesRegisteredToEureka() throws Exception {
        if (services == null || services.isEmpty()) {
            log.info("No dependent services defined.");
            return;
        }
        log.info("Checking if dependent services are registered to eureka.");
        int attempts = 0;
        while (!services.isEmpty()) {
            services.removeIf(this::checkIfServiceIsRegistered);
            TimeUnit.MILLISECONDS.sleep(periodMs);
            if (maxAttempts.intValue() == ++attempts)
                throw new Exception("Max attempts exceeded.");
        }
    }

    private boolean checkIfServiceIsRegistered(String service) {
        try {
            eurekaClient.getNextServerFromEureka(service, false);
            log.info(service + " - registered.");
            return true;
        } catch (Exception e) {
            log.info(service + " - not registered yet.");
            return false;
        }
    }

}

A list of services that the current microservice depends on are defined in.properties file:

depends-on.services[0]=service-id-1 
depends-on.services[1]=service-id-2  

A bean dependentServicesRegisteredToEureka is not being initialized until all services from the list register to Eureka. If needed, annotation @DependsOn("dependentServicesRegisteredToEureka") can be added to beans or components to prevent attempting an initialization before dependentServicesRegisteredToEureka initialize.