It would seem that the couriertcpd service is possibly restarting itself, but somehow fails to startup on some instances.
couriertcpd never restarts itself. The parent process is actually a very small loop that forks off new processes to handle established connections, and then keeps track of them until they die.
I'd be glad to post other information about my setup if anybody has ideas about what may be going on.
The only thing you could possibly do is monitor the parent couriertcpd process using strace. Note that since it could be a while before an occurence of this problem, the log file may get quite large.
If you're running low on memory, and you're running a Linux kernel with OOM killer enabled, the explanation is probably as simple as the kernel explicitly killing couriertcpd in a vain attempt to free up memory.
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