Rails: During asset precompile throws error key must be 16 bytes - ruby-on-rails

Question

I am storing my secret key in environment and /config/environments/production.rb has config.require_master_key = true uncommented
config.require_master_key = true
When running
RAILS_ENV=production bundle exec rake assets:precompile
I get the error
/Users/something/Development/wwwroot/trivial/config/environment.rb:5:in `<main>'
/Users/something/.rbenv/versions/2.5.1/bin/bundle:23:in `load'
/Users/something/.rbenv/versions/2.5.1/bin/bundle:23:in `<main>'
Caused by:
ArgumentError: key must be 16 bytes
/Users/something/Development/wwwroot/trivial/config/environment.rb:5:in `<main>'
/Users/something/.rbenv/versions/2.5.1/bin/bundle:23:in `load'
/Users/something/.rbenv/versions/2.5.1/bin/bundle:23:in `<main>'
Tasks: TOP => environment
any ideas on how to fix this error? What else can I do?

Answer 1

Your problem is that the key you generated is longer of what rails expects https://github.com/rails/rails/issues/33528#issuecomment-412677795
Solution
You can recreate a new one by deleting your master.key and credentials.yml.enc and run
rails credentials:edit

Answer 2

I faced the same issue while setting up a Rails 6.0 application on Ubuntu in production.
I was using the figaro gem for my environment variables.
The issue was that I was copying the content of the secret_key_base instead of the master_key
Here's how I solved it
Delete the previous master.key and the credentials.yml.enc file
Recreate a new master.key and credentials.yml.enc:
rails credentials:edit
OR
EDITOR="code --wait" bin/rails credentials:edit # If you want to use VS Code as your editor
Copy the contents of the master.key, which is of this format:
34d3cc7c5305dde06865acfa473716cd
Replace my RAILS_MASTER_KEY value with the master_key in production:
RAILS_MASTER_KEY: "34d3cc7c5305dde06865acfa473716cd"
And then save it.
Note: You could also experience this issue if you set/specify a wrong RAILS_MASTER_KEY environment variable in your .env files (.env, .env.development, .env.test, .env.production). Say you just want to use it as a placeholder temporarily. This may also throw an error key=': key must be 16 bytes (ArgumentError) if you try to generate new master.key and the credentials.yml.enc files using rails credentials:edit or EDITOR="code --wait" bin/rails credentials:edit
What you have to do is to either provide the right RAILS_MASTER_KEY environment variable in the .env file(s) or comment out the RAILS_MASTER_KEY environment variable if you are not using it.
That's it.
I hope this helps

Answer 3

For me I had to ensure I remove the quotes around the key in my .env file.
It seems my server(AWS ECS Fargate) was counting the "" as part of the key. Locally it was all fine.
Before
RAILS_MASTER_KEY="12345"
After
RAILS_MASTER_KEY=12345

Answer 4

You can run this in your terminal
heroku config:set RAILS_MASTER_KEY=`cat config/master.key`
You can follow the tutorial here