Error: Unable to pip install packages

Symptom: When you install packages, you might occasionally see something like this:

$ pip install <some-package>
Looking in indexes: https://devpi.svc.ngsci.local/root/pypi/+simple/
ERROR: Could not find a version that satisfies the requirement <some-package> (from versions: none)
EROR: No matching distribution found for <some-package>

Because you can't access the internet from Nightingale instances, your ability to pip install depends on an internal PyPI cache, devpi.

You might run into this error when you try to pip install a package that we haven't cached yet, especially if it's a big download. 

The reason for this behavior is that pip expects a response from the package index, but our internal index doesn't respond until after it has succeeded or failed to retrieve the package from PyPI. This relay lag sometimes causes pip timeouts for larger packages. If this is the reason for the error, then your pip install should work after a minute or so.