Terraform Datasources

• Data sources allow data to be fetched or computed in terraform configuration
• Navigate to the aws provider documentation and search for aws_subnet to find the datasources refer here
• Since we can write the query to fetch subnet ids, we can use for each expression of terraform
• The following expression which creates subnet associations can be changed to

resource "aws_route_table_association" "webassociations" {
  count = 2
  route_table_id = aws_route_table.publicrt.id
  subnet_id =  aws_subnet.subnets[count.index].id

  depends_on = [ 
    aws_route_table.publicrt
   ]
  
}

• For New approach Refer Here

• Now lets create an association for private subnets Refer Here

• Now destroy all and recreate

• This error has occured as terraform is trying to query the subnet ids before they are created

• So we need to create subnets first and then apply the whole template (This is not a good practice)

terraform apply -target="aws_subnet.subnets" .
terraform apply .

• depending on dynamic values by writing a data source will work in incremental mode of deployment, whenever you are trying to create the complete infra data sources if not used correctly might lead to these situations.
• So for this reason lets revert back to what we had for creating route table associations
• Refer Here for the changes reverted and the length function used.