Captain Webhook just restarts the service. The systemd service file looks like this, and auto-pulls on every restart: https://www.pastery.net/xrutdm/
I will update the post with the above, thank you.
I'm in a very similar situation as what you've got described, and I'll start in on that part of the project sometime in the next month or so.
Also been looking at Elastic Beanstalk for deployments. Have you looked at that yet?
I don't know how you'd communicate with nginx inside the container to tell it to switch, though, or how you would be able to know when all requests were done on the old container. Hopefully there's an easy way.
Too bad that a single SIGHUP becomes so complicated with containers, but I guess it's a tradeoff.
About the Beanstalk, I haven't looked into it too much, maybe that can help with deployment. I'd be grateful if you could let me know how it worked, if you ever try it out.