apollo-configservice/src/main/java/com/ctrip/framework/apollo/configservice/util/InstanceConfigAuditUtil.java/InstanceConfigAuditUtil/assembleInstanceConfigKey
class InstanceConfigAuditUtil:  private String assembleInstanceConfigKey(long instanceId, String configAppId, String configNamespace) {
    return STRING_JOINER.join(instanceId, configAppId, configNamespace);
  }