First you follow very simple instructions how to start 2-container. After that you mostly need only
./launcher bootstrap web_only && ./launcher destroy web_only && ./launcher start web_only ) 2>&1 | tee ~/$(date +%Y-%m-%d_%H-%M-%S)-upgrade.log'
tee part is only for logging, because browsing it is easier (for me) than tmux feed I’m using.
But basically it is totally same than using app.yml and rebuild, except it bothers users much less. Sure, there is data-container, but it needs love and caring very rarely — and if you will do some more sophisticated tricks with container, you propably know what to do and when with containers too.
If upgraiding fails with 2-container you have still a forum up and alive, when single one will crash.
So, only starting is a bit more demanding, but instructions are quote clear. I would say using mail-reveiver is more harder task, if using Amazon SES.