apollo-portal/src/main/java/com/ctrip/framework/apollo/portal/environment/PortalMetaDomainService.java/PortalMetaDomainService/getDomain
class PortalMetaDomainService:    public String getDomain(Env env) {
        String metaServerAddress = getMetaServerAddress(env);
        // if there is more than one address, need to select one
        if (metaServerAddress.contains(",")) {
            return selectMetaServerAddress(metaServerAddress);
        }
        return metaServerAddress;
    }