Puppet versions prior to 3.6.0 use API v1 at https://forge.puppetlabs.com/v1/, but this breaks since the site began redirecting to forge.puppet.com. The installation commands fail with:
Passing --module_repository https://forge.puppet.com/ is a workaround.
If URLs beneath /api/v1 (such as https://forge.puppetlabs.com/api/v1/releases.json?module=puppetlabs-ntp) didn't redirect, this would fix the issue for these old clients.
This seems to be affecting a few users:
I've also submitted a bug to Ubuntu as 14.04's shipped Puppet version is 3.4.3 and is affected by this issue: https://bugs.launchpad.net/ubuntu/+source/puppet/+bug/1594316