I was using Let's Encrypt before successfully with Gluu, a couple of times. I used instructions provided on the official site, the certbot approach. I didn't set up auto-renewal, but the rest worked fine.
Please follow instructions on [this page](https://certbot.eff.org/lets-encrypt/centosrhel7-apache). If it won't work for you, list all the steps you did, and exactly what error do you see (screenshot, full text from console etc).
@Sahil.Arora, could you share you thoughts? I believe QA uses Let's Encrypt on regular basis.