Can't migrate at install time

[jlecour]

== 20180523145630 DeviseCreateUsers: migrating ================================
-- create_table(:users)
   -> 0.0241s
-- add_index(:users, :email, {:unique=>true})
rake aborted!
StandardError: An error has occurred, all later migrations canceled:

Mysql2::Error: Specified key was too long; max key length is 767 bytes: CREATE UNIQUE INDEX `index_users_on_email`  ON `users` (`email`) 
/localhome/jlecour/work/intra/chexpire/db/migrate/20180523145630_devise_create_users.rb:41:in `change'
/home/jlecour/.rbenv/versions/2.5.1/bin/bundle:23:in `load'
/home/jlecour/.rbenv/versions/2.5.1/bin/bundle:23:in `<main>'

Caused by:
ActiveRecord::StatementInvalid: Mysql2::Error: Specified key was too long; max key length is 767 bytes: CREATE UNIQUE INDEX `index_users_on_email`  ON `users` (`email`) 
/localhome/jlecour/work/intra/chexpire/db/migrate/20180523145630_devise_create_users.rb:41:in `change'
/home/jlecour/.rbenv/versions/2.5.1/bin/bundle:23:in `load'
/home/jlecour/.rbenv/versions/2.5.1/bin/bundle:23:in `<main>'

Caused by:
Mysql2::Error: Specified key was too long; max key length is 767 bytes
/localhome/jlecour/work/intra/chexpire/db/migrate/20180523145630_devise_create_users.rb:41:in `change'
/home/jlecour/.rbenv/versions/2.5.1/bin/bundle:23:in `load'
/home/jlecour/.rbenv/versions/2.5.1/bin/bundle:23:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

[jlecour]

There is a complex issue which depends on the verison of MySQL/MariaDB.

Basically, if you use MySQL < 5.7 (MySQL 5.5 or MariaDB 10.1) the workaround is to force the server to create tables with "utf8" instead of "utf8mb4" :

character-set-server=utf8
collation-server=utf8_general_ci