terraform HCL language reference

4 min read | by Jordi Prats

LC to LT

terraform: Set root device size using launch template: From aws_launch_configuration to aws_launch_template there's no direct equivalent for root_block_device
launch configuration to launch template: On most cases, converting a launch configuration to a launch template shouldn't involve much effort

terraform cidrsubnet() function: We can use the cidrsubnet function to programmatically generate subnets using terraform
terraform lookup() function: With the lookup function we can return a default value if the key is not present on the map
terraform coalesce() function: Using the coalesce function we can pick the first not empty value out of a list
Terraform: jsonencode: Using jsonencode we can generate a comma separated list of quoted strings on terraform
terraform nonsensitive() function: Using the nonsensitive function we can tell terraform that certain variable is no longer sensitive
terraform function: csvdecode: Using the csvdecode function we can use a CSV file as a datasource
terraform function: try: Using the try function we can simulate setting a default value for a map object
terraform function: setproduct: terraform setproduct can be very useful on generating objects by multiplying a set of lists
terraform: hide sensitive information: Starting terraform 0.15 we can instruct it what data is sensitive so it can redact it
terraform one() function: The terraform one() function can help us deal with conditionally included resources
How to apply replace() function to a list of strings in terraform: HCL is a declarative language, even though we can use a for loop to apply the replace function to a list of strings
terraform: Usage of attributes from a conditionally included resource: For resources conditionally included we must use indexed access to it's attributes

terraform state on a Kubernetes Secret: Kubernetes secrets can also be used to store terraform's state
Terraform: Usage of a DynamoDB table for state locking: To use a DynamoDB table is recommended if you are using a remote terraform state on S3

Terraform AWS AMI datasource: Using the aws_ami datasource we can use terraform to look for the latest available AMI
terraform: Using archive_file to update aws_lambda_function: When using archive_file we need to consider how the aws_lambda_function is updated
Terraform: AWS account datasource: There are some datasources avalable for AWS accounts
aws_security_groups return empty list: aws_security_groups cannot, currently, return an empty list of SecurityGroups
Terraform data sources: In terraform a data source can be either any resource or even a remote terraform state
Using a remote terraform state as a datasource: When we need to use a resource created by another team we can use terraform_remote_state for getting it's outputs

sops & terraform: Secrets as Code: By using terraform together with sops we can safely push secrets into AWS Secrets Manager purely as code
kubernetes_manifest: terraform provider for Kubernetes: Using the kubernetes_manifest resource we can push any kind of object into Kubernetes using terraform
Override a terraform provider: Using dev_overrides we can instruct terraform to use a local version of a provider
Provider configuration not present - terraform: Upgrading the terraform state meanwhile we are pushing new changes can lead to weird errors
Terraform: How to properly set the default region for the AWS provider: The argument "region" is required, but was not set: We need to properly set the default region

Terraform: Setting variables using environment: Environment variables can be used to set variables

Using lifecycle ignore_changes to skip changes on a terraform resource: Using the lifecycle block on a terraform resource we can tell which options managed outside of terraform

for_each over tuples in terraform: Using for_each on a tuple will result on an error, let's see how to work around it
terraform: Array of resources using for_each: Using for_each we can create multiple resources using a variable to iterate
terraform: optional nested blocks: Using dynamic blocks we can conditionally decide if we want to include a given nested block
terraform: dynamic blocks: Using dynamic blocks we can dynamically create nested blocks on terraform resources
terraform: conditionally include a resource: Writing terraform modules it is usefull to be able to conditionally include a resource

triggers on the terraform null_resource for updating it: When using null_resource and local-exec sometimes is useful to have a way to refresh it