Cloud9から、heroku環境へdb:migrateが通らない

Cloud9で作成したRailsアプリケーションをherokuへ展開しています。
git push heroku masterまで完了し、次はDB...と思っているんですが、ドハマリしています。

heroku db:migrateを実施すると、下記のエラーメッセージがでます。
（念のため全文記載）

$ heroku run rake db:migrate
rake aborted!
Mysql2::Error: Access denied for user 'ユーザ名'@'ip-10-171-194-27.ec2.internal' (using password: YES)
/app/vendor/bundle/ruby/2.3.0/gems/mysql2-0.4.10/lib/mysql2/client.rb:89:in `connect'
/app/vendor/bundle/ruby/2.3.0/gems/mysql2-0.4.10/lib/mysql2/client.rb:89:in `initialize'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/mysql2_adapter.rb:21:in `new'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/mysql2_adapter.rb:21:in `mysql2_connection'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:759:in `new_connection'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:803:in `checkout_new_connection'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:782:in `try_to_checkout_new_connection'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:743:in `acquire_connection'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:500:in `checkout'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:374:in `connection'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_adapters/abstract/connection_pool.rb:931:in `retrieve_connection'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_handling.rb:116:in `retrieve_connection'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/connection_handling.rb:88:in `connection'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/schema_migration.rb:20:in `table_exists?'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/schema_migration.rb:24:in `create_table'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/migration.rb:1125:in `initialize'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/migration.rb:1007:in `new'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/migration.rb:1007:in `up'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/migration.rb:985:in `migrate'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/tasks/database_tasks.rb:171:in `migrate'
/app/vendor/bundle/ruby/2.3.0/gems/activerecord-5.1.4/lib/active_record/railties/databases.rake:58:in `block (2 levels) in <top (required)>'
/app/vendor/bundle/ruby/2.3.0/gems/rake-12.3.0/exe/rake:27:in `<top (required)>'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/cli/exec.rb:74:in `load'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/cli/exec.rb:74:in `kernel_load'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/cli/exec.rb:27:in `run'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/cli.rb:360:in `exec'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/vendor/thor/lib/thor/invocation.rb:126:in `invoke_command'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/vendor/thor/lib/thor.rb:369:in `dispatch'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/cli.rb:20:in `dispatch'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/vendor/thor/lib/thor/base.rb:444:in `start'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/cli.rb:10:in `start'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/exe/bundle:30:in `block in <top (required)>'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/lib/bundler/friendly_errors.rb:121:in `with_friendly_errors'
/app/vendor/bundle/ruby/2.3.0/gems/bundler-1.15.2/exe/bundle:22:in `<top (required)>'
/app/bin/bundle:3:in `load'
/app/bin/bundle:3:in `<main>'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

どうやら、エラー文の@'ip-10-171-194-27.ec2.internal' がクセモノっぽいんですが、ぐぐっても解決方法が見つからず、困っております。
今回はEC2を使用する予定はないのですが、なぜかEC2からポート指定してMySQLに接続しようとしているみたいです。

以下、現環境の情報。

開発環境

Cloud9
Rails 5.1.4
Ruby 2.4.0
mysql2 0.4.10

database.yml

Ruby
1production:
2  <<: *default
3  adapter:  mysql2
4  username: xxxx  # アプリ名
5  encoding: utf8
6  database: <%= ENV['DB_NAME'] %>
7  username: <%= ENV['DB_USERNAME'] %>
8  password: <%= ENV['DB_PASSWORD'] %>
9  host:     <%= ENV['DB_HOSTNAME'] %> # us-cdbr-iron-east-05.cleardb.netをheroku -config登録
10  port:     <%= ENV['DB_PORT'] %>
11