I'm going to have to dispute your definition of "large system" if it's been running for a mere 6 months and you describe it as if it had a single author. Let me know once it's changed maintenance twice and also once it's changed management twice. Robustness is not about how well a system performs in its initial conditions; it's about how well it responds to change.

Also, from the sounds of it, it doesn't seem like a distributed system. Client-side JS is by its nature a distributed system, dealing with network partitions all the time because end-user internet connections are unreliable.