Side-by-side browser has been retired and is no longer a part of GOV.UK Transition. It was retired due to the extremely low usage, being years after the transition project, which no longer justified the effort to maintain it.
Proxy a web site to preview redirections ahead of it being transitioned to GOV.UK.
$ npm install
$ npm test
$ node server.js
...then you can use nip.io to make it work with localhost, eg:
http://www.justice.gov.uk.side-by-side.127.0.0.1.nip.io:3023/__/#/
Run the server on Heroku. It requires a side-by-side
wildcard subdomain pointed to it:
$ heroku domains:add *.side-by-side.publishing.service.gov.uk
Follow the returned instructions to CNAME the wildcard to Heroku.
By default, the application will take its list of allowed domains from the production
instance of the GOV.UK Transition tool. This can be overridden with the SIDE_BY_SIDE_HOSTS
environment variable. Examples:
SIDE_BY_SIDE_HOSTS=https://transition.publishing.service.gov.uk/hosts
(the default)SIDE_BY_SIDE_HOSTS=file:etc/hosts.json
SIDE_BY_SIDE_HOSTS=https://example.com/hosts