After creating my Ubuntu 20.04 instance with only 8GB, I went into AWS and increased the volume to 50 GiB in the t3.large instance. Yet, back in Ubuntu, that disk space isn't shown anywhere (based on my current Linux abilities...). FileMaker server is loaded on /dev/root and that disk space did not change after the disk space addition.
"fdisk -l" should show the new free space (reboot if it does not).
If /dev/root is the only/last partition on the disk, the "growpart" / "resize2fs" will do the trick, otherwise the more complicated (and fear-inducing) ways like answer 4 there will be needed.
Or, if "fdisk -l" shows the free space, create a new partition in the free space (using fdisk, cfdisk, parted,...), format it using mkfs.ext4, mount it somewhere & add it to /etc/fstab. Then move /opt/FileMaker or /opt/FileMaker/FileMaker\ Server/Data to the new partition and link it to the original place.
Or, I would probably stop FMS, copy all of /opt/FileMaker to the new volume and then mount it as /opt/FileMaker. IMHO the cleanest final setup.
I had the additional problem that Tomcat and MariaDB simply weren't externally reachable when installed on the same machine as FMS. Setting up another Linux instance for these two programs worked perfectly. Baffling. Two days spent on this... Now, it looks like I'll need either a single Windows AWS instance where FMS and Tomcat/MariaDB can run or two Linux instances. It's only money, I guess!