How can I get rid of a nova conflicting dependencies error as I install openstack?

Question

I've been trying to install OpenStack using devstack tools on ubuntu 18.04 and I'm stuck with this error: Cannot install nova because these package versions have conflicting dependencies. It's shown like this:

*INFO: pip is looking at multiple versions of nova to determine which version is compatible with other requirements. This could take a while. ERROR: Cannot install nova because these package versions have conflicting dependencies.

The conflict is caused by: pypowervm 1.1.27 depends on futures>=3.0; python_version == "3.6" The user requested (constraint) futures===3.0.5

To fix this you could try to:

1. loosen the range of package versions you've specified
2. remove package versions to allow pip attempt to solve the dependency conflict

ERROR: ResolutionImpossible: for help visit https://pip.pypa.io/en/latest/user_guide/#fixing-conflicting-dependencies *

Answer 1

Solved:

This is a common error because in Python 3.x, you cannot install futures==3.0.5 and pypowervm==1.1.27 requires futures>=3.0. Even if you plan to downgrade your python version to 2.x, Openstack requires a minimum version of Python>=3.6 to execute and hence it's sort of a deadlock. My answer is a workaround for this deadlock and I plan to create a PR to the repo to resolve it.

The following steps helped me to solve it:

Step 1: Download the Package

wget https://files.pythonhosted.org/packages/55/db/97c1ca37edab586a1ae03d6892b6633d8eaa23b23ac40c7e5bbc55423c78/futures-3.0.5.tar.gz#sha256=0542525145d5afc984c88f914a0c85c77527f65946617edb5274f72406f981df

Step 2: Extract the Package

tar xfvz futures-3.0.5.tar.gz
cd futures-3.0.5/

Step 3: Ignore the exception

sed -i "s/raise type(self._exception), self._exception, self._traceback/raise Exeption(type(self._exception), self._exception, self._traceback)/" concurrent/futures/_base.py

Step 4: All done now, last step to install

sudo python3 setup.py install

I confirmed that this worked for me and many others and please find the source and original link to a whole blogpost of possible Openstack errors you can face during installations.

https://developpaper.com/using-devstack-to-install-openstack-with-one-click-the-detailed-process-and-the-pits-encountered/