I applied online and never heard back.

Several months later, I was referred by a friend at the company and recruited to be an SRE based on my experience. Since the SRE jobs would have required relocation, I opted to interview for a Software Engineer role. I didn't get an offer as a Software Engineer, but based on the feedback from that, I was recruited again the next year as an SRE and was ready to relocate at that time.

The hiring process at Google is very slow. It took several weeks between resuming contact with their recruiter and getting an offer. If you're out of work and looking to get a job ASAP, Google may not be the best choice. If you're in no rush, it can be very worthwhile.

With respect to my NDA, I won't go into details, but I was asked to design a highly-available production service from bare metal all the way to algorithms and data structures.