(3.0.0 3.5.1) ParallelCluster CLI raises exception “module 'flask.json' has no attribute 'JSONEncoder'”

The issue

Due to a recent change in flask, when a version newer than 2.2.4 is installed the ParallelCluster CLI will raise an exception when executing any command. If affected by this issue, the pcluster command will raise an exception with the following message:

AttributeError: module 'flask.json' has no attribute 'JSONEncoder'

Mitigation

To workaround this issue, install the 2.2.4 version of flask with the following command:

python3 -m pip install flask==2.2.4

After updating the dependency, the CLI should work normally.