Upgrading from 8.3.7 to 8.4 conflicts with acquia/blt-project In the composer.json file I added "drupal/core": "~8.4" to the required section. When I run composer update drupal/core --with-all-dependencies, I get the following output.


  Loading composer repositories with package information
  Updating dependencies (including require-dev)
  Your requirements could not be resolved to an installable set of packages.
  
  Problem 1
  
  
  drupal/core 8.4.0 conflicts with acquia/blt-project
  


Why does Drupal 8.4 conflict with acquia/blt-project?
The problem was a line in my composer.json file which is prevent the upgrade from happening.

In the "conflict" section, there's a line "drupal/core": "&gt;=8.4.0-alpha1"
I have to remove that line and also run the following commands to complete the upgrade.

composer update --lock
composer require acquia/lightning:^3.0 acquia/blt:^8.9 --no-update
composer update acquia/lightning --with-all-dependencies