For migrating between Redis databases on Heroku, when the source database doesn't support the sync Redis command

redis-migrate.rb

# For migrating between Redis databases on Heroku, when the source database doesn't support sync
# This is useful for migrating away from Redis Cloud, for example.
require "redis"

# You need to have created a new database first, with
# heroku addons:create heroku-redis:hobby-dev -a $APP
# OR
# heroku addons:create heroku-redis:premium-0 -a $APP


APP         = "YOUR_APP".freeze  # The Heroku app name
NEW_DB_NAME = "REDIS_URL".freeze # Change this if your new Redis database has a different name

SOURCE_DB = `heroku config:get REDISCLOUD_URL -a #{APP}`.chomp
DEST_DB   = `heroku config:get #{NEW_DB_NAME} -a #{APP}`.chomp

source = Redis.new(url: SOURCE_DB)
target = Redis.new(url: DEST_DB)

`heroku ps:scale worker=0 -a #{APP}`
`heroku maintenance:on -a #{APP}`

source.keys("*").each do |key|
  data = source.dump key
  # puts key, data
  target.restore key, 0, data
end

# You might need to change this to be appropriate for you
`heroku config:set REDIS_PROVIDER=#{NEW_DB_NAME} -a #{APP}`
`heroku maintenance:off -a #{APP}`
`heroku ps:scale worker=1 -a #{APP}`