Error installing mysql2psql: ERROR: Failed to build gem native extension - ruby

Question

Im trying to build a docker container to migrate a MySql database to a Postgresql. Plan is to then ad images for each server in a docker-compose.yml, but my initial image build fails
My dockerfile:
FROM ruby:2.4.0
RUN apt-get update && apt-get install -y \
build-essential \
nodejs \
mysql-client \
libmysqlclient-dev \
libpq-dev \
RUN mkdir -p /app
WORKDIR /app
RUN gem install mysql2psql
But I get an error:
Building native extensions. This could take a while...
ERROR: Error installing mysql2psql:
ERROR: Failed to build gem native extension.
current directory: /usr/local/bundle/gems/mysql-2.8.1/ext/mysql_api
/usr/local/bin/ruby -r ./siteconf20180130-1553-1id0936.rb extconf.rb
checking for mysql_ssl_set()... yes
checking for rb_str_set_len()... yes
checking for rb_thread_start_timer()... no
checking for mysql.h... yes
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/usr/local/bin/$(RUBY_BASE_NAME)
--with-mysql-config
--without-mysql-config
extconf.rb:67:in `<main>': uninitialized constant Config (NameError)
Did you mean? RbConfig
CONFIG
To see why this extension failed to compile, please check the mkmf.log which can be found here:
/usr/local/bundle/extensions/x86_64-linux/2.4.0/mysql-2.8.1/mkmf.log
extconf failed, exit code 1
Gem files will remain installed in /usr/local/bundle/gems/mysql-2.8.1 for inspection.
Results logged to /usr/local/bundle/extensions/x86_64-linux/2.4.0/mysql-2.8.1/gem_make.out
What am I missing?

Answer 1

First, you have an error in your Dockerfile: you should not put \ on the end of the RUN command.
The problem you are having installing this gem relates to it just being too old. This gem requires gem mysql -v '2.8.1', which is only compatible with Ruby 2.1 or earlier.
So, to get this working, you could change your ruby version, by using FROM ruby:2.1 or using another gem for the task, for example: https://github.com/maxlapshin/mysql2postgres.
Working solution:
FROM ruby:2.1
RUN apt-get update && apt-get install -y \
build-essential \
nodejs \
mysql-client \
libmysqlclient-dev \
libpq-dev
RUN mkdir -p /app
WORKDIR /app
RUN gem install mysql2psql