xBis7 opened a new pull request, #51586:
URL: https://github.com/apache/airflow/pull/51586
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We are using Airflow with Kubernetes and we are occasionally experiencing
failures due to DNS resolution blips. These failures are temporary and usually
take mere seconds to go away.
The failure is occurring while a new db connection is required and Airflow
performs a DNS lookup on the db hostname.
This can be resolved by retrying to establish the DB connection but there
are better approaches.
This patch is adding a config flag that enables a db discovery check. If the
option is turned on, we run a `socket.getaddrinfo(...)` on the db hostname to
see if it can be resolved.
This approach is chosen for the following reasons
* `socket.getaddrinfo(...)` is less expensive and much faster than retrying
to create a new session
* not all kinds of DNS errors are temporary and must be retried.
* e.g. a wrong value on the database config option `sql_alchemy_conn` is
also a DNS error but it shouldn't be retried
* in case of an exception, the error that we get from
`socket.getaddrinfo(...)` carries an error code which can be used for
distinguishing between the different DNS errors
* `create_session()` will give us an exception with the same error message
but no other info
* the error code is more reliable than the error message which might be
prone to changes during a new version update of the component that is
generating it
I've added a unit test and an integration test. The integration test hasn't
been added under the `integration` package because it doesn't need any
integration other than a db backend. The code is db agnostic but for the test I
used specifically a postgres backend because it's easier to just hardcode a
postgres address.
The check is turned off by default.
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