consul客户端必须配置微服务实例名称和ID,微服务启动的时候需要将名称和ID注册到注册中心,后续微服务之间调用也需要用到.

名称可以通过以下两种方式配置,优先级从高到低.两个都不配置则默认服务名称为application

spring.cloud.consul.discovery.service-name 
spring.application.name

ID可以通过多个配置项配置,下面的五种配置都可以,优先级从高到低.

spring.cloud.consul.discovery.instance-id   
vcap.application.instance_id  
spring.application.name和spring.application.instance_id搭配,'-'分隔
spring.application.name和server.port搭配,'-'分隔
spring.application.name  
spring.application.instance_id  

如果不配置启动会报错,相关日志如下,从日志中也可以看出,配置要求必须以字母开始,字母或数字结尾.

Caused by: java.lang.IllegalArgumentException: Consul service ids must not be empty, must start with a letter, end with a letter or digit, and have as interior characters only letters, digits, and hyphen: 8081
    at org.springframework.cloud.consul.serviceregistry.ConsulAutoRegistration.normalizeForDns(ConsulAutoRegistration.java:179) ~[spring-cloud-consul-discovery-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.cloud.consul.serviceregistry.ConsulAutoRegistration.getInstanceId(ConsulAutoRegistration.java:170) ~[spring-cloud-consul-discovery-2.0.1.RELEASE.jar:2.0.1.RELEASE]
    at org.springframework.cloud.consul.serviceregistry.ConsulAutoRegistration.registration(ConsulAutoRegistration.java:78) ~[spring-cloud-consul-discovery-2.0.1.RELEASE.jar:2.0.1.RELEASE]

代码详见org.springframework.cloud.consul.serviceregistry.ConsulAutoRegistration

    public static ConsulAutoRegistration registration(AutoServiceRegistrationProperties autoServiceRegistrationProperties, ConsulDiscoveryProperties properties, ApplicationContext context, List<ConsulRegistrationCustomizer> registrationCustomizers, HeartbeatProperties heartbeatProperties) {
        NewService service = new NewService();
        //注册到consul服务端时显示的微服务名称,优先级从高到低:
        //配置项spring.cloud.consul.discovery.service-name 
        //配置项spring.application.name
        //默认值application
        String appName = getAppName(properties, context.getEnvironment());
        //注册到consul服务端时显示的微服务Id,优先级从高到低:  
        //配置项spring.cloud.consul.discovery.instance-id
        //配置项vcap.application.instance_id
        //配置项spring.application.name和spring.application.instance_id,用':'拼接
        //配置项spring.application.name和server.port,用':'拼接
        //配置项spring.application.name  
        //配置项spring.application.instance_id
        //注意,内部的normalizeForDns方法,用于规范化应用名称、ID等,把非数字字符串转换成'-'连接符  
        //比如spring.application.name=sc--test,server.port=8080,拼成的id为sc--test:8080,经过normalizeForDns方法就转换成了sc-test-8080  
        service.setId(getInstanceId(properties, context));
        if(!properties.isPreferAgentAddress()) {
            service.setAddress(properties.getHostname());
        }
        //微服务应用名称也必须符合规范,字母开始,字母或数字结尾  
        service.setName(normalizeForDns(appName));  
        //设置标签,spring.cloud.consul.discovery.tags
        service.setTags(createTags(properties));
        if(properties.getPort() != null) {
            service.setPort(properties.getPort());
            setCheck(service, autoServiceRegistrationProperties, properties, context, heartbeatProperties);
        }

        ConsulAutoRegistration registration = new ConsulAutoRegistration(service, autoServiceRegistrationProperties, properties, context, heartbeatProperties);
        customize(registrationCustomizers, registration);
        return registration;
    }

    //字符串不能为空,首字符必须为字母,尾字符必须为字母或数字,所有非字母数字的字符统一转换成'-'连接符,同时多个连续连接符转换成一个'-'.  
    public static String normalizeForDns(String s) {
        if(s != null && Character.isLetter(s.charAt(0)) && Character.isLetterOrDigit(s.charAt(s.length() - 1))) {
            StringBuilder normalized = new StringBuilder();
            Character prev = null;
            char[] var3 = s.toCharArray();
            int var4 = var3.length;

            for(int var5 = 0; var5 < var4; ++var5) {
                char curr = var3[var5];
                Character toAppend = null;
                if(Character.isLetterOrDigit(curr)) {
                    toAppend = Character.valueOf(curr);  
                } 
                //不为数字和字母的字符转换成'-'分隔符,连续多个非字母数字字符转换成一个'-'分隔符  
                //这里做了一层判断,只有在前一个字符为字母数字的时候,才把当前的字符转换成'-'; 如果前一个为'-'则这个字符忽略不拼接.  
                //其实这里的prev只有在第一次的时候为null但是第一次的时候走不到else if这个条件  
                else if(prev == null || prev.charValue() != 45) {
                    toAppend = Character.valueOf('-');
                }

                if(toAppend != null) {
                    normalized.append(toAppend);
                    prev = toAppend;
                }
            }

            return normalized.toString();
        } else {
            throw new IllegalArgumentException("Consul service ids must not be empty, must start with a letter, end with a letter or digit, and have as interior characters only letters, digits, and hyphen: " + s);
        }
    }