So there is me, a junior who started half a year ago, my supervisor and a third guy who essentially run the hardware development department. The other dude just left for military service for 18 weeks. Which leaves me with his work. Running half the department as a junior...

Bone up on networking and whatever OS you’re running. If you’re on premise learn raid configs. If you’re cloud based learn the console of your chosen service. Learn how your backups work for production and do a mock restore to spare resources. Excellent opportunity to learn a lot of infrastructure stuff that many developers never get to learn. With just one supervisor you’re likely to have keys to the castle. Be cautious and smart, don’t break anything, but recognize how lucky you are to have that chance