There are many online resources about using SSH keys to achieve passwordless, cron-initiated tasks like rsyncing some files around. Most of these assume your SSH key is either not encrypted with a password, or that you're running the related command in an interactive session.
What I couldn't easily find recently was a way to make sure that a script initiated via cron on OS X 10.10 (Yosemite) and that uses an SSH key that is encrypted with a password would have access to that key as managed by the current login session's
This problem manifested itself with the following kind of output from my rsync command - being used to back up some files from a remote server - when it was executed via cron:
Permission denied, please try again. Permission denied, please try again. Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password). rsync: connection unexpectedly closed (0 bytes received so far) [receiver] rsync error: unexplained error (code 255) at /SourceCache/rsync/rsync-45/rsync/io.c(453) [receiver=2.6.9]
If I ran the same command from the shell prompt it worked fine.