Your Terraform plan,
explained.

Terraform will perform the following actions:

  # aws_security_group.api will be updated in-place
  ~ resource "aws_security_group" "api" {
        id          = "sg-0a1b2c3d4e5f"
        name        = "api-sg"
      ~ ingress {
          ~ cidr_blocks      = [
              - "10.0.0.0/8",
              + "0.0.0.0/0",
            ]
            from_port        = 5432
            protocol         = "tcp"
            to_port          = 5432
        }
    }

  # aws_db_instance.primary must be replaced
  -/+ resource "aws_db_instance" "primary" {
      ~ engine_version       = "14.6" -> "15.4"
      ~ identifier           = "prod-db" -> "prod-db-v2"
      + deletion_protection  = true
        ...
        allocated_storage    = 100
        instance_class       = "db.t3.large"
    }

  # aws_ecs_service.api will be updated in-place
  ~ resource "aws_ecs_service" "api" {
      ~ desired_count = 2 -> 4
        id            = "arn:aws:ecs:..."
    }

Plan: 1 to add, 2 to change, 0 to destroy.