How to keep roborumble running forever
Funny thing that I don't do anything special. I just run the clients on my own computers. They all currently have Debian stable (stretch) linux distribution with openjdk-8 java. The robocode is installed manually in my home folder.
I run clients in the 'screen' sessions, so if I get disconnected the session survives. From time to time, I restart it manually, mostly for selfish reason of a quicker bot list upadate. But the current run is almost 100 days straight without interruption. My machines have 4 to 6 cores, so I just do normal office load (browsing, youtube, short term calculations) on them as well.
One more thing. I just checked that I client consumes about 4GB of memory (including virtual one) after that 100 days.
I would suspect that VPS shares you CPU with other virtual OSes and kills CPU consuming process forcefully.
For many years that I run robocode clients, I never had any problem with sporadic crashes. The restart happens only if my home looses power and UPS runs dry.