[Ppm] Versioning for DAP drafts

[Christopher Patton <[e-mail]>]

HI all,

As we are in the midst of considering changes for DAP-02, some implementers
(myself included) are finding themselves in the position of needing to
support multiple drafts simultaneously. As such, I think it's time that we
consider what our needs are for maintaining interop with older drafts.

One option for deployments is to "lock" the Aggregator endpoints to
specific drafts. For example, the Leader's base URL might be
dap-01.leader.example.com, indicating that the leader supports DAP-01 only.
One downside is that this makes determining whether a peer speaks a given
version happens out-of-band. I imagine this might lead to failure modes
that are hard to diagnose.

After kicking this round with a few people off-list, here are a few options:
1. We could version the MIME types for each of the messages. E.g., instead
of "application/dap-report" (see [1]) we could have
`application/dap-02-report".
2. We could send the version in a separate HTTP Header, e.g., "DAP-Version:
draft-02".
3. We could version the HTTP endpoints in-band. E.g., instead of POSTing
reports to "/upload", clients would POST to "/02/upload".
4. We could encode the version number in the message payload itself.

Thoughts on these options? Any alternatives?

Best,
Chris P.


[1]
https://ietf-wg-ppm.github.io/draft-ietf-ppm-dap/draft-ietf-ppm-dap.html#name-application-dap-report-medi