状況

長らく触っていなかったRails5のプロジェクトをデプロイしようとしたら、下記のエラーでデプロイできなかった。

OpenSSH keys only supported if ED25519 is available (NotImplementedError)
net-ssh requires the following gems for ed25519 support:
 * ed25519 (>= 1.2, < 2.0)
 * bcrypt_pbkdf (>= 1.0, < 2.0)
See https://github.com/net-ssh/net-ssh/issues/565 for more information
Gem::LoadError : "ed25519 is not part of the bundle. Add it to your Gemfile."
(Backtrace restricted to imported tasks)
cap aborted!
NotImplementedError: OpenSSH keys only supported if ED25519 is available
net-ssh requires the following gems for ed25519 support:
 * ed25519 (>= 1.2, < 2.0)
 * bcrypt_pbkdf (>= 1.0, < 2.0)
See https://github.com/net-ssh/net-ssh/issues/565 for more information
Gem::LoadError : "ed25519 is not part of the bundle. Add it to your Gemfile."

Tasks: TOP => rbenv:validate
(See full trace by running task with --trace)

解決方法

development用にこちらを追加し bundle install したら解決しました。

diff --git a/Gemfile b/Gemfile
index 0898d25..067fd75 100644
--- a/Gemfile
+++ b/Gemfile
@@ -68,6 +68,9 @@ group :development do
 group :development do
   gem 'capistrano-rails'
   gem 'capistrano-rbenv'
   gem 'capistrano-bundler'
   gem 'capistrano-yarn'
   gem 'capistrano-passenger', '>= 0.1.1'

+  gem 'ed25519'
+  gem 'bcrypt_pbkdf'
+