In your digital ocean instance, use the following cloud-init script
#cloud-config
runcmd:
- SCRIPT_URL=https://gist.githubusercontent.com/amingilani/09499c28a21a975cf84d51f7f5a68327/raw/gitlab-runner-install.sh
- tmux new-session -s "InstallGitlabRunner" "curl $SCRIPT_URL | bash"