[Pulp-dev] Pulp3 Applicability Design thoughts (and Katello)

[Justin Sherrill]

There have been some design discussions going on around applicability 
(https://hackmd.io/ydvHuzXNRA6T9eXx6cqy5A) in pulp3.

There are some big changes compared to pulp2, including:

* Package profile, module profile,and repository list have to be 
uploaded on every applicability computation

* Calls for applicability are not asynchronous (which makes sense as 
they are one profile at a time).

Also keep in mind that due to the complexity of all the information 
needed, Katello has been the primary (and sometimes the only?) user of 
the service.

For an example of what this might looks like, consider a repository that 
syncs some new packages.  For 10,000 clients, it has to send the full 
package profiles for all 10,000 clients, as well as the other 
information in 10,000 api calls.  In Addition our task workers will have 
to wait around for all 10,000 clients to be calculated.  One last point 
is that katello already knows all the NVREA's for the rpms, which rpms 
are in which repositories, which artifacts are in which modules, and 
which packages are in what errata.

Given all this, does it make sense for pulp to calculate the 
applicability?  Or does it make sense for katello to?

This assumes that no one else wants to use applicability in pulp3 (and 
given the barrier to entry is even higher than it was in pulp2, that may 
be possible).

Justin