First, the code resources:
Page 237: rumbl_umbrella/apps/rumbl/mix.exs
Note: That this file is missing.
Page 238: rumbl_umbrella/apps/rumbl/lib/rumbl/application.ex
Note. This file is included but the original application, rumbl, also had support for telemetry and there’s no reference in the book for it. I’m guessing that telemetry remains within the rumbl_web application.
Page 238: rumbl_umbrella/apps/rumbl_web/lib/rumbl_web/endpoint.ex
Note: This file is included in the resources but the book’s instructions and this file are not in sync with one another.
Page 238: apps/rumbl_web/lib/rumbl_web/channels/presence.ex
Note: This file is included in the resources but the book’s instructions and this file are not in sync with one another.