# depends\_on

用来表示服务之间的依赖关系。服务的依赖关系会导致下面的行为：

* docker-compose up会按照依赖顺序启动服务。下面的示例中，db和redis都在web之前启动。
* docker-compose up SERVICE自动包含SERVICE的依赖。在下面示例，docker-compose up web也会创建和启动db和redis。
* docker-compose stop按照依赖顺序停止服务。下面的示例中，web在db和redis之前被停止。

```
 version: "3.8"
 services:
   web:
     build: .
     depends_on:
       - db
       - redis
   redis:
     image: redis
   db:
     image: postgres
```

Note:

* depends\_on在启动web之前，不会等待db和redis进入ready状态。只会等待它们被启动。如果需要等待一个服务进入ready状态。参考[控制启动顺序](https://docs.docker.com/compose/startup-order/)来解决这个问题。
* 版本3不再支持depends\_on的condition形式。
* 当通过版本3的Compose文件在swarm节点上部署一个stack时，depends\_on选项会被忽视。


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