Out of Memory (OOM) is an error that occurs when an instance runs out of RAM.
The first thing to check if you encounter this is how much RAM was assigned to the problem instance. You can do this by expanding the details of the instance and scrolling down to the "Limits" and "Requests" sections.
Checking RAM allocation
The Requests amount defines the amount of memory that is guaranteed to be available to the instance
The Limits amount defines the amount of memory that the instance may not exceed.
To increase the amount of resources for your instances, edit your Environment Configuration settings under the "Settings" tab.
Viewing currently running processes using top
Sometimes you will need to see exactly what processes are running on an instance and how much memory each process is using in order to debug an OOM error. To do this, you can connect to a terminal for that instance and run the top command.
This will show the memory use by each process on that instance.