client.rb

require 'drb/ssl'

DRb.start_service
DRb.config.merge!(
  SSLVerifyMode: OpenSSL::SSL::VERIFY_PEER,
  SSLCACertificateFile: 'pki/ca.crt',
  SSLPrivateKey: OpenSSL::PKey::RSA.new(File.read('client/pki/private/ManveruClient.key')),
  SSLCertificate: OpenSSL::X509::Certificate.new(File.read('pki/issued/ManveruClient.crt')),
)

obj = DRbObject.new_with_uri('drbssl://localhost:1234')
p obj.size

server.rb

require 'drb/ssl'


DRb.start_service(
  'drbssl://localhost:1234',
  {},
  SSLVerifyMode: OpenSSL::SSL::VERIFY_PEER | OpenSSL::SSL::VERIFY_FAIL_IF_NO_PEER_CERT,
  SSLCACertificateFile: 'pki/ca.crt',
  SSLPrivateKey: OpenSSL::PKey::RSA.new(File.read('pki/private/ca.key')),
  SSLCertificate: OpenSSL::X509::Certificate.new(File.read('pki/ca.crt')),
  SSLVerifyCallback: ->(ok, c){ ok },
)
DRb.thread.join