Why is the postgres server unstable?

Question

PostgreSQL

There is a ubuntu 16.04 server on vps. On it, a parser is launched using the crontab, which saves the data in the postgres database. The interval is large enough, it is unlikely that the matter is in the load. For the second time in 2 weeks, the database server hangs up. After the first time, I thought that it might be worth restarting the server every day and the problem would disappear, but no. There is a process, but on any connection from the outside or locally issues

could not connect to server: Connection refused
        Is the server running on host xhostx and accepting
        TCP/IP connections on port xportx?

Of the settings, only basic + access from the Internet on a specific port to users. What can be and how to look for a problem?
UPD: The parser is launched every ten minutes, but judging by the logs, the last successful launch was at 13:10, and the next launch occurred only at 13:37 and then the database server did not connect. Could it be vps?

Answer 1

it is obvious that you have 512 mb of memory
it is obvious that in the latest versions of pg the cache setting was raised from 128 mb to 4 GB
and probably due to lack of memory pg dies
see dmesg after it becomes unavailable