290 Ruby 2.7 support for Rails 2.3 LTS

Updated . Posted . Visible to the public. Deprecated.

Please read our consolidated guide to "modern Rubies" instead.


You can find the updated guide here.

Rails 2.3 LTS Show archive.org snapshot works with Ruby 1.8.7, Ruby 2.5, and Ruby 2.7. Typical web apps see a 2x to 4x performance boost by switching from Ruby 1.8.7 to Ruby 2.5+. "Support" means that upgrading a Rails 2.3 application to Ruby 2.5 will not require Rails related monkey patches.

However, upgrading will still require some effort for the majority of Rails 2.3 applications, since your own code as well as some third-party gems will most likely have compatibility issues. You should only attempt this as a somewhat experienced Ruby developer, and only if you have a good automatic test suite, or if you're confident that you can manually test your application.

So far, we managed to upgrade two medium-sized applications of our own without major issues, in 1-2 days of effort each. It did require a few dozen minor changes, and we could only do this so quickly due to a very high test coverage. The upgraded apps run at roughly twice their former speed.

Upgrade workflow overview

  1. If you haven't already, switch to bundler Show archive.org snapshot and migrate all config.gem lines to your Gemfile.

  2. Update to the latest version of Rails 2.3 LTS.

  3. Switch your Ruby version to 2.5.x. (You can also first go to 2.3 and then 2.5 in a second step).

  4. Add test-unit version 1.2.3 with require: false to your Gemfile (as a top-level gem and not inside the group :test).

  5. Run bundle install. Make minimal version upgrades to your gems until all can be installed. See below

  6. In config/preinitializer.rb, add a line

    Encoding.default_external = Encoding::UTF_8
  7. In case you already were running on a Ruby > 1.8.7 and have made some Rails monkey patches yourself, remove them.

  8. Check script/server, script/console etc. The first require line should look like this:

    require File.expand_path('../../config/boot',  __FILE__)
  9. Run script/console and fix all errors. If you get a "cannot load such file" error, try running script/server instead to get a full stacktrace. See below on how to fix common errors.

  10. Run script/server and fix all errors until a page renders.

  11. Run tests and fix remaining errors.


We recommend upgrading your RubyGems version to a modern 2.x version. This requires you to use bundler to manage your gems Show archive.org snapshot . Please see our RubyGems guide for additional details.

Third-party gems

Your application will probably depend on a bunch of other gems, and some of those might be incompatible with newer Rubies. The most common case are gems with native extensions that no longer compile.

You will have to check, whether these gems have an updated compatible version, can be removed, might be fixed with a monkey-patch, or have to be replaced.

An incomplete list of known incompatibilities:

  • date-performance -> remove this, no longer necessary
  • fastercsv -> no longer required, Ruby now has builtin CSV
  • mysql -> no longer compiles on Ruby 2.5, see below
  • rspec -> we have a working fork Show archive.org snapshot of rspec 1.3.2, see below
  • sass -> Current version (3.4.x) work


The mysql gem does no longer work on Ruby 2.5. Instead, use mysql2, in a 0.2.x version (< 0.3 in your Gemfile should do).

mysql2 is mostly a drop in replacement for mysql. The main API difference is that you might get casted values (i.e. Time objects instead of strings) when you use some low-level methods of ActiveRecord, such as select_values.

RSpec 1

If you application uses Rspec 1.x for testing, the easiest way forward is to upgrade rspec and rspec-rails to their latest RSpec 1 versions (1.3.2 for RSpec). You will also need to use our fork of rspec, so change your Gemfile to

gem "rspec", "=1.3.2", git: 'https://github.com/makandra/rspec.git', branch: '1-3-lts'

You probably also want to use our fork or rspec-rails which fixes a few test assertions:

gem "rspec-rails", "=1.3.5", git: 'https://github.com/makandra/rspec-rails.git', branch: '1-3-lts'

Common errors when upgrading

The following is a list of issues we encountered in our own code:

  • The YAML parser has changed from Syck to Psych. Some .yaml files need to be fixed for Psych. On common case can be found in default locale files. Instead of

    order: [:day, :month, :year]


    - :day
    - :month
    - :year

    You also now need to quote strings starting with * or &.

    Finally, if you made use of ActiveRecord's serialize feature, you might want to check that serialized data in your database can still be loaded.

  • lambdas (but not procs) have started to check their arguments. You can no longer call a lambda with additional arguments, if the block does not take any.
    Fix this by simply switching the offending (or possible all) lambdas to procs.

  • Some methods in Ruby's standard library have changed:

    • object.respond_to?(:a_protected_method) used to be true, but is now false. You can use object.respond_to?(:a_protected_method, true) (which will also be true for private methods, however).
    • object.id no longer aliases object.object_id
    • Array("line 1\nline 2") no longer splits on linebreaks. Use "line 1\nline 2".lines instead if you used Array for that purpose.
    • Array+to_s used to work like Array#join, but now works like Array#inspec. Use Array#join explicitly.
    • "some words".each is gone. Use "some words".split.each.
    • A few methods no longer accept symbols instead of strings ("foo".starts_with?(:f) is now an error):
  • You can potentially run into issues with String encoding. In general, everything should always be encoded as UTF-8. If you deal with binary data or lowlevel operations (like String#unpack), you must potentially use String#force_encoding or String#encode.

  • Some default libraries are gone:

    • Instead of FasterCSV, use CSV. It has the same Api, but can deal with encodings.

    • iconv is no longer in the standard library. You can add is a gem, or replace it with String#force_encoding / String#encode:

      # old
      converter = Iconv.new('UTF-8//IGNORE', 'WINDOWS-1252')
      # new
      text.force_encoding('WINDOWS-1252').encode('UTF-8', undef: :replace, invalid: :replace)
  • Fixnum deprecation warnings
    In Ruby 2.4+ Fixnum and Bignum are deprecated and replaced by a unified Integer class. This mostly just causes deprecation warnings but not actual errors, since Fixnum internally resolves to Integer.

    If a third-party gem uses Fixnum and you want to remove the deprecation errors, you can often manually define a Fixnum class in the gems namespace. For example, we've added the following initializer to one of our projects:

    # config/initializer/fixnum_deprecation_fixes.rb
    # will_paginate
    WillPaginate::Fixnum = Integer
    BootstrapPagination::Fixnum = Integer
    # axlsx
    Axlsx::Fixnum = Integer
Tobias Kraze
Last edit
Tobias Kraze
Source code in this card is licensed under the MIT License.
Posted by Tobias Kraze to Rails LTS documentation (2017-09-06 14:11)