Harden the terraform configuration

[Joonalai]

Some examples:

• Move db to private subnet
• Use bastion host to access db

Useful links:

• Look some examples here

[Rikuoja]

While at it, fix the conflict between lb security group and security group rule resources. Causes recreating/destroying resources between runs.

From https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/security_group_rule

Terraform currently provides both a standalone Security Group Rule resource (a single ingress or egress rule), and a Security Group resource with ingress and egress rules defined in-line. At this time you cannot use a Security Group with in-line rules in conjunction with any Security Group Rule resources. Doing so will cause a conflict of rule settings and will overwrite rules.

[Rikuoja]

Lambda needs VPC connections:

https://www.maxivanov.io/deploy-aws-lambda-to-vpc-with-terraform/

[Rikuoja]

VPC and security group rules implemented. DB can only be accessed from the ec2 instance in the same VPC.