Proposal: how to make incompatible changes - versioning

[Andrew Jeffery]

On Fri, 24 Apr 2020, at 01:27, Joseph Reynolds wrote:
> On 4/23/20 7:11 AM, Alexander Amelkin wrote:
> > 15.04.2020 02:00, Joseph Reynolds пишет:
> >> Proposal: how to make incompatible changes
> >>
> >> This is a proposal to add guidelines for making incompatible changes 
> >> to OpenBMC interfaces.  Is it okay to make incompatible changes? Yes, 
> >> IMHO: the project will continuously break compatibility in various 
> >> ways, and its users will adapt.  The main idea is to minimize churn 
> >> and make it easier for users to adapt.
> >>
> >> As the OpenBMC project moves forward with new releases, it will make 
> >> changes that necessarily break existing use cases.  My 
> >> recommendations are:
> >> - Try hard to maintain forward compatibility.  For example, maintain 
> >> all of the BMC's intended user interfaces.
> >> - Identify changes that break compatibility.  Briefly describe the 
> >> use case, what breaks, how a user can adapt, and cross-link technical 
> >> discussions (Gerrit reviews, issues, emails).
> >> - Work with maintainers to determine which incompatible changes get 
> >> merged and what documentation is needed.
> >> - Give users time to adapt to incompatible changes.  For example, 
> >> deprecate interfaces in a previous release.
> >> - List incompatible changes in the [release notes][] so community 
> >> members will know they have to adapt, and link to how to adapt.
> >>
> >>
> > I'd say that any incompatible change must be reflected in the 
> > interface version.
> >
> > As far as I understand, RedFish has all the interfaces strictly 
> > specified and those specifications are bound to a specific RedFish 
> > version that is then encoded in the URL (e.g. /redfish/v1/).
> >
> > Any other interface should have a similar approach. A more relaxed 
> > one, if we keep our own flavor of REST, could be that each interface 
> > could have a Version property (probably also encoded in the REST URL).
> >
> > That way, any user trying to access an old interface (thus via a 
> > non-existant URL) would get a 404.
> >
> > Internally, for inter-process dbus communication the interface version 
> > could be checked during compile time to prevent problems that couldn't 
> > be detected by compiler/linker automatically. Those problems are, for 
> > instance, incompatible change in the meaning of the values of a property.
> 
> Agreed.  The question to ponder: What is our REST API versioning 
> strategy?  What  best practices do we follow?

The D-Bus specification already recommends how to version D-Bus interfaces:

https://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-names-interface

Andrew