This article is a translation from https://qiita.com/kawasaki/items/dcaf5716c3fd5e2fe69f

Digest version to set up the secret key in the production environment in Rails 5.1

1. $ rails secrets:setup -> copy the long secret key in the first line and set it as an environment variable RAILS_MASTER_KEY when executing rails
2. $ rails secret -> you will get the longer key; copy it
3. $ EDITOR=vim rails secrets:edit write the following and save it from vim

Errors in the production environment when I run 'rails server'

Ruby on Rails. Contribute to rails/rails development by creating an account on GitHub. I am new to Rails 4, and do not understand the use of secretkeybase under config/secrets.yml in Rails 4. Can you please explain this concept? Also, when I am working in the production environment, I am prompted to set the secretkey with devise.rb, config.secretkey, and secretkeybase. Rails stores secrets in config/credentials.yml.enc, which is encrypted and hence cannot be edited directly. Rails uses config/master.key or alternatively looks for environment variable ENV'RAILSMASTERKEY' to encrypt the credentials file. The credentials file can be stored in version control, as long as master.

I've developped my application happily in the development environment. But it's high time I prepared for the production environment, and I tried

$ rails server --environment production

and got
An unhandled lowlevel error occurred. The application logs may have details.

Oh, no...
Next, I tried
$ rails secrets:setup

which was introduced in Rails 5.1. But the error still remained. Going down in to the rails library, I got the point where I was wrong.

Rails No Master.key Generated Number

Anyway, you'll get the following output wehn you run rails secrets:setup

The encryption key 'a1e98ed29c40d7453a06bebeb815c0f3' in the first line is the most important key to protect the whole application and you must keep it secret. The key is automatically written down to config/secrets.yml.key.
Never commit it to your git repository, NEVER!
But usually you'll not commit it because the file config/secrets.yml.key is automatically added to .gitignore, so that the file is not to be committed.

For rails execution, you need either to import config/secrets.yml.key from somewhere or to set the secret key in the environment variable RAILS_MASTER_KEY.

Actually, this in only the half of the necessary settings because what you did is to make a key to lock config/secrets.yml.enc, you treasure box. You still need to store your treasure.
This file, secrets.yml.enc is an encrypted yml file using your key. It looks like as follows.

To edit this file (if you use vim),
$ EDITOR=vim rails secrets:edit

The file looks like as follows.

Everything is commented out and nothing is specified above. You have to specify secret_key_base beneath production which is a secret key used for Cookie encryption. It is recommended to generate the secret key by using 'rails secret'.

Rails No Master.key Generated Download

Then, save it in your config/secrets.yml.enc by doing

Rails No Master.key Generated Lyrics

Now, you have no error regarding the secret key in Rails.

Rails No Master.key Generated Home

By the way, you can store any kind of secret information here including database passwords. e.g.

You can use the encrypted database password from your code by
Rails.application.secrets.postgresql_password
e.g. in config/database.yml.