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Another change is a requirement to allow list hosts that the rails server will respond to. Avalon by default will allow the host set in the `domain.host` setting as well as any set in the RAILS_ADDITIONAL_HOSTS environment variable. The docker-compose config (both the development environment in avalon and the avalon-docker environment) allows the avalon host which docker creates for its internal network. If you connect to your avalon instance using a different hostname then these, you will probably need to set RAILS_ADDITIONAL_HOSTS environment variable or make changes to config/initializers/default_host.rb. See https://blog.saeloun.com/2019/10/31/rails-6-adds-guard-against-dns-rebinding-attacks.html for more details.
Blacklight
Blacklight 7 changes include the upgrade of bootstrap to 4, changes to search builders, and switching the /catalog json endpoints to return standard JSON-API. If you have customized the CatalogController, any of the search builders, or any of the catalog views, you may need to make changes to ensure compatibility. See the Blacklight 7 release notes for more details: https://github.com/projectblacklight/blacklight/releases/tag/v7.0.0
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