Capistranoを使用して自動デプロイを行いたいがbundle exec cap production deployを実行するとエラーが出る。

Question

問題点

Capistranoを用いて各種設定を行い、ローカル環境で

bundle exec cap production deploy

を行った所

#<Thread:0x00007fa3d8d94ad0@/Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/runners/parallel.rb:10 run> terminated with exception (report_on_exception is true):
Traceback (most recent call last):
	21: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/runners/parallel.rb:12:in `block (2 levels) in execute'
	20: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/backends/abstract.rb:31:in `run'
	19: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/backends/abstract.rb:31:in `instance_exec'
	18: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/capistrano-rbenv-2.2.0/lib/capistrano/tasks/rbenv.rake:10:in `block (3 levels) in <top (required)>'
	17: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/backends/abstract.rb:61:in `test'
	16: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/backends/abstract.rb:148:in `create_command_and_execute'
	15: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/backends/abstract.rb:148:in `tap'
	14: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/backends/abstract.rb:148:in `block in create_command_and_execute'
	13: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/backends/netssh.rb:130:in `execute_command'
	12: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/backends/netssh.rb:177:in `with_ssh'
	11: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/backends/connection_pool.rb:63:in `with'
	10: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/backends/connection_pool.rb:63:in `call'
	 9: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh.rb:251:in `start'
	 8: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh.rb:251:in `new'
	 7: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh/transport/session.rb:88:in `initialize'
	 6: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh/transport/session.rb:88:in `new'
	 5: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh/transport/algorithms.rb:153:in `initialize'
	 4: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh/transport/algorithms.rb:278:in `prepare_preferred_algorithms!'
	 3: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh/transport/algorithms.rb:278:in `map'
	 2: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh/known_hosts.rb:29:in `each'
	 1: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh/known_hosts.rb:29:in `each'
/Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/net-ssh-6.1.0/lib/net/ssh/transport/algorithms.rb:278:in `block in prepare_preferred_algorithms!': undefined method `ssh_type' for nil:NilClass (NoMethodError)
	1: from /Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/runners/parallel.rb:11:in `block (2 levels) in execute'
/Users/black/.rbenv/versions/2.6.5/lib/ruby/gems/2.6.0/gems/sshkit-1.21.2/lib/sshkit/runners/parallel.rb:15:in `rescue in block (2 levels) in execute': Exception while executing as ec2-user@<Elastic IP>: undefined method `ssh_type' for nil:NilClass (SSHKit::Runner::ExecuteError)
(Backtrace restricted to imported tasks)
cap aborted!
SSHKit::Runner::ExecuteError: Exception while executing as ec2-user@<Elastic IP>: undefined method `ssh_type' for nil:NilClass


Caused by:
NoMethodError: undefined method `ssh_type' for nil:NilClass

と出力された。

解決すると考えた仮説

Caused by:の後述にエラー箇所が記載。
'ssh_type'というメソッドが存在しないと考え、設定した箇所を見直したが見当たらなかった。

解決に参考になりそうなソースコード

Palarel.rb

require 'thread'

module SSHKit

  module Runner

    class Parallel < Abstract
      def execute
        threads = hosts.map do |host|
          Thread.new(host) do |h|
            begin
              backend(h, &block).run
            rescue ::StandardError => e
              e2 = ExecuteError.new e
              raise e2, "Exception while executing #{host.user ? "as #{host.user}@" : "on host "}#{host}: #{e.message}"
            end
          end
        end
        threads.each(&:join)
      end
    end

  end

end