Rails 5 redirect root domain to www and vice versa

rails-6-redirect-www.rb

# example.com => www.example.com
match '(*any)', to: redirect(subdomain: 'www'), via: :all, constraints: { subdomain: false }
# www.example.com => example.com
match '(*any)', to: redirect(subdomain: false), via: :all, constraints: {subdomain: 'www'}

# caveat
# subdomain is anything from 3rd level domain, so for example.co.uk domains the syntax will be the following:
# example.co.uk => www.example.co.uk
match '(*any)', to: redirect(subdomain: 'www.example'), via: :all, constraints: { subdomain: 'example' }
# www.example.co.uk => example.co.uk
match '(*any)', to: redirect(subdomain: 'example'), via: :all, constraints: { subdomain: 'www.example' }