MongoDB terminates when it runs out of memory

As per MongoDB BOL Here Changed in version 3.4: Values can range from 256MB to 10TB and can be a float. In addition, the default value has also changed.

Starting in 3.4, the WiredTiger internal cache, by default, will use the larger of either:

50% of RAM minus 1 GB, or
256 MB.

With WiredTiger, MongoDB utilizes both the WiredTiger internal cache and the filesystem cache.

Via the filesystem cache, MongoDB automatically uses all free memory that is not used by the WiredTiger cache or by other processes.

The storage.wiredTiger.engineConfig.cacheSizeGB limits the size of the WiredTiger internal cache. The operating system will use the available free memory for filesystem cache, which allows the compressed MongoDB data files to stay in memory. In addition, the operating system will use any free RAM to buffer file system blocks and file system cache.

To accommodate the additional consumers of RAM, you may have to decrease WiredTiger internal cache size.

For further your ref WiredTiger Storage Engine and Configuration File Options

Actually, if you look closely, it's not mongod that dies for "out-of-memory", it's the kernel OOM (out of memory) manager that kills mongod, because it has the biggest memory usage.

Yes, you can try to solve the problem with monngodb configuration parameter cacheSizeGB, but in the container environment, it is better to use cgroups to limit the resources that any of your three containers get.