Gitlab CI failed to connect to several number of services

Hi! I have my continious delivery on gitlab-ci. It builds my project.
For the last couple of days, I see that Gitlab CI cannot install needed dependencies while running.

Sometimes, it failed to connect to rubygems.org, but Rubygems is working good.
Sometimes, it failed to connect http://deb.debian.org/, but it is also working good!!

What is going on? How can I fix it?