OpenJDK 64-Bit Server VM warning: Failed to reserve shared memory. (error = 1), (error = 12), (error = 12)

Question

I created two LEMP servers at Digitalocean & installed Solr 8.7.0 on Ubuntu 20.04:

1. USD 5 Droplet 1GB RAM + 1vCPU
2. USD 80 Droplet 16GB RAM + 2vCPUs