Best way to generate a migration timestamp

You can use timestamp.to_s(:number).

There are also other formats:

:db            # => "2007-12-04 00:00:00"
:number        # => "20071204000000"
:short         # => "04 Dec 00:00"
:long          # => "December 04, 2007 00:00"
:long_ordinal  # => "December 4th, 2007 00:00"
:rfc822        # => "Tue, 04 Dec 2007 00:00:00 +0000"
:iso8601       # => "2007-12-04T00:00:00+00:00"

Time.now.utc.strftime("%Y%m%d%H%M%S")

@timestamp = Time.now.strftime("%Y%m%d%H%M%S")