API: Not all Conflicts (409) should be retry-able

[Lucas Alvares Gomes]

Currently the way the interaction between the python-ironicclient and the Ironic API service works is that for Conflict (409) returned by the API we should retry it a number of times.

While this assumption is valid for some cases e.g node is currently locked and doing some operation so you have to try it later. It's not valid for others e.g when registering a port with a mac address that is already registered.

So following the example of registering a port with a duplicated MAC address, the request will take ~30s before it actually returns the error. This is not something that the server will eventually fix so retrying doesn't make much sense. See paste: [1]

Currently the non retry-able Conflict(409) in our API (IMHO) are:

* Registering a node with duplicated "name", "instance_uuid" or "uuid".
* Registering a port with duplicated "uuid" or "address"
* Registering a chassis with duplicated "uuid"
* Trying to delete a node which is in a provision state where it can't be deleted (e.g ACTIVE, CLEANING, etc...)

Suggestions:

1) We need a way to indicate when 409 is retry-able or not. One way to do it is by using the "Retry-After"[2] HTTP header and having the client to respect it.

If specified the client should wait the number of seconds specified in that header and try again (We could keep the options of "--max-retries" and "--retry-interval" for the client, but the "--retry-interval" by default will be None and if specified it overwrite the seconds passed by the server in the "Retry-After" header)

If "Retry-After" is not specified in the header, the client should not retry the request.

2) Use a different HTTP code for non retryable errors. I would suggest us to use Unprocessable Entity (422) for it. Since the syntax of the request is fine we can't use BadRequest (400)

This won't need any change in the client.

[1] http://paste.openstack.org/show/354956/
[2] http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.37
[3] https://tools.ietf.org/html/rfc4918#section-11.2

[Dmitry Tantsur (divius)]

Note that change of error code is not entirely backward compatible change..