When attempting to run as directed, I received this error on the database step:
#<Mysql2::Error: Can't connect to MySQL server on 'database' (115)>
Couldn't create database for {"adapter"=>"mysql2", "encoding"=>"utf8", "pool"=>5, "username"=>"root", "password"=>"root", "database"=>"standardfile", "host"=>"database", "port"=>nil}, {:charset=>"utf8"}
(If you set the charset manually, make sure you have a matching collation)
Created database 'standardfile'
I made the following change to docker-compose.yml
Line 25, from DB_HOST: database to DB_HOST: db, and it ran without error.