Currently, setting the '[oslo_messaging] direct_mandatory_flag' config
option to 'True' (the default) will result in a 'MessageUndeliverable'
exception being raised when sending a reply if a RabbitMQ queue is
missing [1]. It was the responsibility of the application to handle
this exception, however, many applications are not doing so. This has
resulted in a number of bug reports.
Start handling this error condition, using a retry loop to attempt to
resend the message and work around any temporary glitches. Since
attempting to send a reply will will no longer raise an exception,
there is little benefit in retaining the '[oslo_messaging]
direct_mandatory_flag' config option: users setting this to False will
simply not benefit from the retry logic and improved logging added
here. This option is already deprecated though and will be fully
removed in a future release.
[1] https://www.rabbitmq.com/channels.html
Change-Id: Id5cddbefbe24ef100f1cc522f44430df77d217cb
Closes-Bug: #1905965
4937949dff