Rails 6 adds rails server handler option,
to specify the server (webrick/thin/puma…) we want to use.
Before Rails 6
The rails server --help signature looked like this
rails server [puma, thin etc] [options]
To start rails server using thin we needed to execute below command
$ bin/rails server thin
We were not specifying any explicit option for the rack server we intended to use.
In Rails 6
Now we need to specify the handler --using or -u for the rack server.
The new command is
$ bin/rails server --using thin
or
$ bin/rails server -u thin
The above changes also notify error message if a missing or mistyped rack server name is specified.
So if tin is passed instead of thin as a rack server
$ bin/rails server -u tin
It will throw an error denoting mistyped rack server
Could not find server "tin". Maybe you meant "thin" or "cgi"?
Run `rails server --help` for more options.
In case a server which is not present in Gemfile is passed
$ bin/rails server -u unicorn
It will throw below error denoting missing rack server
Could not load server "unicorn". Maybe you need to the add it to the Gemfile?
gem unicorn
Run `rails server --help` for more options.
