About the DAG discovering not synced between scheduler and webserver

[Song Liu <so...@outlook.com>]

Hi,

When add a new dag, sometimes we can see:

```
This DAG isn't available in the web server's DagBag object. It shows up in this list because the scheduler marked it as active in the metadata database.
```

In the views.py, it will collect DAGs under "DAGS_FOLDER" by instantiate a DagBag object as bellow:

```
dagbag = models.DagBag(settings.DAGS_FOLDER)
```

So that webserver will depends on its own timing to collect DAGs, but why not just simply to query metadata db ? since if a DAG is active in DB now it can be visible in web at the time.

Could someone share something behind this design ?

Thanks,
Song

答复: About the DAG discovering not synced between scheduler and webserver

[Song Liu <so...@outlook.com>]

For example bellow two API from webserver, it is getting the dag out of one global dagbag object, which is instantiated when the app instance is created, so it (app/webserver) can't be aware of any new DAGs until this app is re-launched again ? What does this design for ?


```

dagbag = models.DagBag(settings.DAGS_FOLDER)



    @expose('/run')
    def run(self):
        dag_id = request.args.get('dag_id')
        dag = dagbag.get_dag(dag_id)


    @expose('/trigger')
    def trigger(self):
        dag_id = request.args.get('dag_id')
        dag = dagbag.get_dag(dag_id)
```



________________________________
发件人: 刘松(Brain++组) <li...@megvii.com>
发送时间: 2018年5月13日 5:39:40
收件人: dev@airflow.incubator.apache.org
主题: Re: About the DAG discovering not synced between scheduler and webserver

Hi,


It seems that Airflow handles bellow situation currently:


-  DAGs discovered in scheduler, but not discovered by webserver yet

-  DAGs discovered in webserver, but not discovered by scheduler yet


I still don't quite understand why there is the discovering logic separately in scheduler and webserver, based on my understanding webserver only needs to display the orm_dags from metadb, is there any requirement or design consideration besides this ?


Many thanks for any information.


Thanks,

Song

________________________________
From: Song Liu <so...@outlook.com>
Sent: Saturday, May 12, 2018 7:58:43 PM
To: dev@airflow.incubator.apache.org
Subject: About the DAG discovering not synced between scheduler and webserver

Hi,

When add a new dag, sometimes we can see:

```
This DAG isn't available in the web server's DagBag object. It shows up in this list because the scheduler marked it as active in the metadata database.
```

In the views.py, it will collect DAGs under "DAGS_FOLDER" by instantiate a DagBag object as bellow:

```
dagbag = models.DagBag(settings.DAGS_FOLDER)
```

So that webserver will depends on its own timing to collect DAGs, but why not just simply to query metadata db ? since if a DAG is active in DB now it can be visible in web at the time.

Could someone share something behind this design ?

Thanks,
Song

Re: About the DAG discovering not synced between scheduler and webserver

["刘松 (Brain++组)" <li...@megvii.com>]

Hi,


It seems that Airflow handles bellow situation currently:


-  DAGs discovered in scheduler, but not discovered by webserver yet

-  DAGs discovered in webserver, but not discovered by scheduler yet


I still don't quite understand why there is the discovering logic separately in scheduler and webserver, based on my understanding webserver only needs to display the orm_dags from metadb, is there any requirement or design consideration besides this ?


Many thanks for any information.


Thanks,

Song

________________________________
From: Song Liu <so...@outlook.com>
Sent: Saturday, May 12, 2018 7:58:43 PM
To: dev@airflow.incubator.apache.org
Subject: About the DAG discovering not synced between scheduler and webserver

Hi,

When add a new dag, sometimes we can see:

```
This DAG isn't available in the web server's DagBag object. It shows up in this list because the scheduler marked it as active in the metadata database.
```

In the views.py, it will collect DAGs under "DAGS_FOLDER" by instantiate a DagBag object as bellow:

```
dagbag = models.DagBag(settings.DAGS_FOLDER)
```

So that webserver will depends on its own timing to collect DAGs, but why not just simply to query metadata db ? since if a DAG is active in DB now it can be visible in web at the time.

Could someone share something behind this design ?

Thanks,
Song