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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AIRFLOW-2839) Answer a question in doc: what if I have connections with the same conn_id in both metadata and environment variables?
Date Sun, 05 Aug 2018 18:09:00 GMT

    [ https://issues.apache.org/jira/browse/AIRFLOW-2839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16569532#comment-16569532
] 

ASF GitHub Bot commented on AIRFLOW-2839:
-----------------------------------------

kaxil closed pull request #3678: [AIRFLOW-2839] Refine Doc Concepts->Connections
URL: https://github.com/apache/incubator-airflow/pull/3678
 
 
   

This is a PR merged from a forked repository.
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diff --git a/docs/concepts.rst b/docs/concepts.rst
index f879ced012..09c1293806 100644
--- a/docs/concepts.rst
+++ b/docs/concepts.rst
@@ -333,6 +333,17 @@ from ``BaseHook``, Airflow will choose one connection randomly, allowing
 for some basic load balancing and fault tolerance when used in conjunction
 with retries.
 
+Airflow also has the ability to reference connections via environment
+variables from the operating system. But it only supports URI format. If you
+need to specify ``extra`` for your connection, please use web UI.
+
+If connections with the same ``conn_id`` are defined in both Airflow metadata
+database and environment variables, only the one in environment variables
+will be referenced by Airflow (for example, given ``conn_id`` ``postgres_master``,
+Airflow will search for ``AIRFLOW_CONN_POSTGRES_MASTER``
+in environment variables first and directly reference it if found,
+before it starts to search in metadata database).
+
 Many hooks have a default ``conn_id``, where operators using that hook do not
 need to supply an explicit connection ID. For example, the default
 ``conn_id`` for the :class:`~airflow.hooks.postgres_hook.PostgresHook` is


 

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> Answer a question in doc: what if I have connections with the same conn_id in both metadata
and environment variables?
> ----------------------------------------------------------------------------------------------------------------------
>
>                 Key: AIRFLOW-2839
>                 URL: https://issues.apache.org/jira/browse/AIRFLOW-2839
>             Project: Apache Airflow
>          Issue Type: Improvement
>          Components: configuration, Documentation
>            Reporter: Xiaodong DENG
>            Assignee: Xiaodong DENG
>            Priority: Critical
>             Fix For: 2.0.0
>
>
> We can define connections either in metadata database or environment variables.
>  
> However, how about there are connections with the same conn_id in both metadata database
and environment variables? Will one of them be picked? Which one? Or a random one will be
picked?
>  
> The answer is: Airflow will check environment variables first.[https://github.com/apache/incubator-airflow/blob/master/airflow/hooks/base_hook.py#L70] 
The "random picking" mechanism will only be applicable for multiple connections with the same
conn_id in metadata database (if there is no connection with the same conn_id defined in environment
variables).
>  
> This should be made clear in the documentation.



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