How to SSH into a server using Kamal? ERROR (Net::SSH::AuthenticationFailed): Exception while executing on host 111.111.111.11: Authentication failed for user user@111.111.111.11

[csalmeida]

I am trying to deploy a Ruby on Rails application using Kamal, on a Digital Ocean droplet.
The app makes use of Rails 7.1.3 and includes a Dockerfile.

Following the documentation I started by installing Kamal using the alias to spin up a container (added it to .zshrc):

alias kamal='docker run -it --rm -v "${PWD}:/workdir" -v "/run/host-services/ssh-auth.sock:/run/host-services/ssh-auth.sock" -e SSH_AUTH_SOCK="/run/host-services/ssh-auth.sock" -v /var/run/docker.sock:/var/run/docker.sock ghcr.io/basecamp/kamal:latest'

Then I ran kamal init which created a deploy.yml and a few other files related to hooks, followed by kamal setup and I got the following error:

kamal setup
  INFO [05fe4a3f] Running /usr/bin/env mkdir -p .kamal on 111.111.111.11
  Finished all in 0.1 seconds
  ERROR (Net::SSH::AuthenticationFailed): Exception while executing on host 111.111.111.11: Authentication failed for user user@111.111.111.11

[csalmeida]

Changing the volume path for the SSH folder in the Docker command allowed Kamal to SSH into the server:

alias kamal='docker run -it --rm -v "${PWD}:/workdir" -v "${HOME}/.ssh:/root/.ssh" -v "/run/host-services/ssh-auth.sock:/run/host-services/ssh-auth.sock" -e SSH_AUTH_SOCK="/run/host-services/ssh-auth.sock" -v /var/run/docker.sock:/var/run/docker.sock ghcr.io/basecamp/kamal:latest'

Output:

kamal setup
  INFO [f932c1af] Running /usr/bin/env mkdir -p .kamal on 111.111.111.11
  INFO [f932c1af] Finished in 1.062 seconds with exit status 0 (successful).
  INFO [8d6509a9] Running /usr/bin/env mkdir -p .kamal/locks on 111.111.111.11
  INFO [8d6509a9] Finished in 0.051 seconds with exit status 0 (successful).

However, it is brought up that this is not the safest solution, I assume because the whole .ssh folder is being copied into the container for Kamal to use.

Probably using gem install kamal instead of the container method would avoid this issue all together but I haven't tried.