Data-Sources

• For creating ec2 machine, we need to provide

  • subnet-id
  • security group
  • key value pair

• One approach create every thing and use the attributes.

• If we want to use existing subnet-id, security group and key-value pair, we need to know ids, for this terraform has data sources which can query the information from providers.

• Every provider gives various data sources much like resources.

• Lets create a simple data source to pull the information of default subnet and create a new subnet

data "aws_vpc" "default" {
    default = true
}

resource "aws_subnet" "extra" {
    cidr_block = "172.31.48.0/20"
    vpc_id = "${data.aws_vpc.default.id}"
}

Terraform provisioning

• Execution of scripts/ansible/chef after creation of Virtual Machines is supported by terraform provisioners. Refer

Backends

• Two tf developers have same terraform script and they have applied terraform, it creates two different resources, as the state file is stored on individual developers laptop
• Now, if we want to restrict these two developers in such a way, whenever they execute terraform it should not create two different but one resource.
• Terraform supports backends, to store state remotely and terraform also supports locking feature to avoid simultaneous access to terraform state.
• Refer