I worked at CDC full-time
Great training and great atmosphere
You will have to be open to moving around a lot for consistent promotion
I applied online. The process took 6 weeks. I interviewed at CDC in February 2017.
Email a resume and cover letter to the listed departmental email. I believe there may have been a brief writing sample request as well. After several weeks, they called me to set up a group phone interview that was exactly 15 minutes long. After the phone call, they gave me two days to submit two recommendations and transcripts (I think it was transcripts. It was a little while ago, but I know they needed something in addition to recommendations). I declined to pursue the process.