Ignore ResourceExists errors from bbs_apps_client

[Gerg]

• This is a re-implementation of 133486e
• This reverts commits:
  • e321fa8
  • fc96bb6
  • 133486e
• This error can be raised by BBS when there is a race condition between
  the CC syncer and CC API when creating an LRP for a process
• Since we want to desire a process anyway, it already existing (with
  the correct version) is likely not an error case. Thus, we can behave
  idempotently.
• Improvements from previous implementation:
  • No longer ignores other types of APIErrors in
    desire_app_handler.rb
  • No longer coupled to the exact error message coming from BBS

[Gerg]

We do lose out on this update. I think the syncer will get to it anyway (or already got to it, since this is a race condition). I'll think about it some more.

[Gerg]

Yea, looking at client.update_app, it's getting the LRP based on the CC process's guid and version. If the versions match between the LRP and the CC process, then no update is needed (that's the purpose of version).

Thus, I don't think this additional update is needed.

[Gerg]

Discovered while reviewing #4452

[Gerg]

Reproduction steps:

❯ bosh ssh api
...
$ sudo su -
# /var/vcap/jobs/cloud_controller_ng/bin/console
...
> c = ::CloudController::DependencyLocator.instance.bbs_apps_client
...
> c.desire_app ProcessModel.first
CloudController::Errors::ApiError: Runner error: Process Guid: fba69784-a41a-4e8c-bf10-7f42e172718f: the requested resource already exists
from /var/vcap/data/packages/cloud_controller_ng/7e6a3d36ede40c3a067e44f3c9971388757df5ad/cloud_controller_ng/lib/cloud_controller/diego/bbs_apps_client.rb:123:in `handle_diego_errors'

[Gerg]

Manual testing

1. bosh ssh api
2. sudo su -
3. /var/vcap/packages/cloud_controller_ng/cloud_controller_ng/lib/cloud_controller/diego/desire_app_handler.rb:

   module VCAP::CloudController
     module Diego
       class DesireAppHandler
         class << self
           def create_or_update_app(process, client)
             # if (existing_lrp = client.get_app(process))
             #   client.update_app(process, existing_lrp)
             # else
               client.desire_app(process)
             # end
           end
         end
       end
     end
   end

4. monit restart cloud_controller_ng
5. tail -f /var/vcap/sys/log/cloud_controller_ng/cloud_controller_ng.log
6. In another terminal: cf map-route --hostname nap3 nip bertram.app-runtime-interfaces.ci.cloudfoundry.org (or anything else that will go through desire_app_handler).

Results:

1. Command succeeds

   Mapping route nap3.bertram.app-runtime-interfaces.ci.cloudfoundry.org to app nip in org org / space space as admin...
   OK
   

2. Error log:

   {"timestamp":"2025-08-25T23:07:23.104702127Z","message":"desire.app.response","log_level":"info","source":"cc.bbs.apps_client","data":{"request_guid":"b8eedebd-51b2-49b7-ad9b-f2ca57920873::4afab2b2-4e0f-4546-9aae-58190b7a343a","user_guid":"9adc9b33-9f27-4246-8269-30564dc0655b","b3_trace_id":"b8eedebd51b249b7ad9bf2ca57920873","b3_span_id":"31b15314866356dd","process_guid":"dabdf66a-02a9-43cf-b0cc-8de30e63e2d4-f9a550ce-8b15-4f40-bc2d-d810ee9810e2","error":"\u003cDiego::Bbs::Models::Error: type: :ResourceExists, message: \"the requested resource already exists\"\u003e"},"thread_id":51620,"fiber_id":51640,"process_id":21,"file":"/var/vcap/data/packages/cloud_controller_ng/ddd60da3712747339f983245f3d0eaf84ccba870/cloud_controller_ng/lib/cloud_controller/diego/bbs_apps_client.rb","lineno":16,"method":"block in desire_app"}