1) @s3w47m88 Could you post the complete and verbose output (add -vvvv)?
ansible-playbook deploy.yml -e env=staging -e site=staging.OMITTED.com -vvvv
2) It looks like you’re using the default web_user so could you SSH in to the server as the web user, run this command, and share the output?
web@staging.OMITTED.com:~$ ls -alh /home/web/.ssh
drwx------ 2 web www-data 4.0K Mar 30 19:24 .
drwxr-xr-x 7 web www-data 4.0K Mar 30 19:24 ..
-rw------- 1 web www-data 399 Mar 30 18:43 authorized_keys
-rw-r--r-- 1 web www-data 2.1K Apr 1 01:54 known_hosts
We need to be sure that the /home/web/.ssh/known_hosts file exists and has permissions and ownership that will work for the web user (-rw-r--r-- 1 web www-data). If the file presence, permissions, or ownership differ from above, it will be helpful if you share any ideas on how such defaults might have been changed, and share which cloud hosting you’re using (e.g., DigitalOcean, AWS, etc.) and which base Ubuntu image you’re using from that provider.
3) Could you ensure your version of Trellis includes known_hosts-related updates from roots/trellis#799?
The known_hosts feature is not essential for all users. You may not need it. To temporarily get past this blocking task in your deploy, you could try commenting out the list of known_hosts and add this empty list definition just above or below:
known_hosts: []
Here is more conceptual info on known_hosts as related to this task in Trellis.