ruby-on-rails - capistrano デプロイメントによる pg のインストール エラー

Question

Rails 2.3.8 アプリがあります。gemfile に pg がありますが、展開後にエラーが表示されます

servers: ["apphost"]
    [apphost] executing command
 ** [out :: apphost] Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
 ** [out :: apphost] 
 ** [out :: apphost] /usr/local/bin/ruby extconf.rb
 ** [out :: apphost] checking for pg_config... no
 ** [out :: apphost] No pg_config... trying anyway. If building fails, please try again with
 ** [out :: apphost] --with-pg-config=/path/to/pg_config
 ** [out :: apphost] checking for libpq-fe.h... no
 ** [out :: apphost] Can't find the 'libpq-fe.h header
 ** [out :: apphost] *** extconf.rb failed ***
 ** [out :: apphost] Could not create Makefile due to some reason, probably lack of
 ** [out :: apphost] necessary libraries and/or headers.  Check the mkmf.log file for more
 ** [out :: apphost] details.  You may need configuration options.
 ** [out :: apphost] 
 ** [out :: apphost] Provided configuration options: