I'm trying to create a module in Terraform that can be instantiated multiple times with different variable inputs. Within the module, how do I reference resources when their names depend on an input variable? I'm trying to do it via the bracket syntax ("${aws_ecs_task_definition[var.name].arn}") but I just guessed at that.
(Caveat: I might be going about this in completely the wrong way)
Here's my module's (simplified) main.tf file:
variable "name" {}
resource "aws_ecs_service" "${var.name}" {
name = "${var.name}_service"
cluster = ""
task_definition = "${aws_ecs_task_definition[var.name].arn}"
desired_count = 1
}
resource "aws_ecs_task_definition" "${var.name}" {
family = "ecs-family-${var.name}"
container_definitions = "${template_file[var.name].rendered}"
}
resource "template_file" "${var.name}_task" {
template = "${file("task-definition.json")}"
vars {
name = "${var.name}"
}
}
I'm getting the following error:
Error loading Terraform: Error downloading modules: module foo: Error loading .terraform/modules/af13a92c4edda294822b341862422ba5/main.tf: Error reading config for aws_ecs_service[${var.name}]: parse error: syntax error
I was fundamentally misunderstanding how modules worked.
Terraform does not support interpolation in resource names (see the relevant issues), but that doesn't matter in my case, because the resources of each instance of a module are in the instance's namespace. I was worried about resource names colliding, but the module system already handles that.
The picture below shows what is going on.
The terraform documentation does not make their use of "NAME" clear versus the "name" values that are used for the actual resources created by the infrastructure vender (like, AWS or Google Cloud).
Additionally, it isn't always "name=, but sometimes, say, "endpoint= or even "resource_group_name= or whatever.
And there are a couple of ways to generate multiple "name" values -- using count, variables, etc., or inside tfvar files and running terraform apply -var-file=foo.tfvars
Related
I am trying to create dependency between multiple sub modules which should be able to create the resource individually as well as should be able to create the resource if they are dependent on each other.
basically i am trying to create multiple VMs, and based on the ip addresses and vip ip address returned as the output i want to create the lbaas pool and lbaas pool members.
i have kept the project structure as below
- Root_Folder
- main.tf // create all the vm's
- output.tf
- variable.tf
- calling_module.tf
- modules
- lbaas-pool
- lbaas-pool.tf // create lbaas pool
- variable.tf
- output.tf
- lbaas-pool-members
- lbaas-pool-members.tf // create lbaas pool member
- variable.tf
- output.tf
calling_module.tf contains the reference to the lbaas-pool module and lbaas-pool-members, as these 2 modules are dependent on the output of the resource generated by main.tf file.
It is giving below error:
A managed resource has not been declared.
As the resource has not been generated yet, and while running terraform plan and apply command is trying to load the resource object which has not been created. Not sure with his structure declare the module implicit dependency between the resources so the module can work individually as well as when required the complete stack.
Expected behaviour:
main.tf output parameters should be create the dependency automatically in the terraform version 0.14 but seems like that is not the case from the above error.
Let's say you have a module that takes an instance ID as an input, so in modules/lbaas-pool you have this inside variable.tf
variable "instance_id" {
type = string
}
Now let's say you define that instance resource in main.tf:
resource "aws_instance" "my_instance" {
...
}
Then to pass that resource to any modules defined in calling_module.tf (or in any other .tf file in the same folder as main.tf), you would do so like this:
module "lbaas-pool" {
src="modules/lbaas-pool"
instance_id = aws_instance.my_instance.id
...
}
Notice how there is no output defined at all here. Any output at the root level is for exposing outputs to the command line console, not for sending things to child modules.
Also notice how there is no data source defined here. You are not writing a script that will run in a specific order, you are writing templates that tell Terraform what you want your final infrastructure to look like. Terraform reads all that, creates a dependency graph, and then deploys everything in the order it determines. At the time of running terraform plan or apply anything you reference via a data source has to already exist. Terraform doesn't create everything in the root module, then load the submodule and create everything there, it creates things in whatever order is necessary based on the dependency graph.
I have a root Terraform module that declares a VPC module and other modules such as an EC2 instance that is to launch in the VPC.
In the EC2 module, I read the VPC using the aws_vpc type:
data "aws_vpc" "vpc" {
filter {
name = "tag:Name"
values = [var.name_tag]
}
}
Now this works fine if I declare the modules independently.
But when declaring a root module that declares these other modules separately, I get this failure:
▶ terraform apply
module.cloudwatch.data.aws_ami.ami: Refreshing state...
module.backend.data.aws_vpc.vpc: Refreshing state...
module.backend.data.aws_ami.ami: Refreshing state...
Error: no matching VPC found
on .terraform/modules/backend/main.tf line 1, in data "aws_vpc" "vpc":
1: data "aws_vpc" "vpc" {
So there is a chicken/egg problem here.
I am confused. How can this ever work? If a root module cannot both declare a VPC and then use the aws_vpc data source later to read it into other modules, what is the use of these data sources? I would appreciate advice on the best practice here. Should I simply not use aws_vpc and instead read in the VPC ID as an output elsewhere?
To me this sounds like you are declaring both a resource like
resource "aws_vpc" "example" {}
AND data-provider like
data "aws_vpc" "example" {}
in order to access something from the data like data.aws_vpc.example.arn. This is not needed and in fact is causing your error. If both is in the same terraform state, you can simply drop the data "aws_vpc" "example" {} and refer to the resource by e.g. resource.aws_vpc.example.arn.
The data provider is actually only needed in cases in which you are referring to a resource that is created somewhere else like something created manually, by a different provisioning engine (or also by terraform, but in a different layer).
You have not mentioned your query very specifically.
As far as I understand from your question, you have declared VPC in root module and want to use it's id or arn, etc from this, right?
So, in this scenario, you must have specify the perfect path of your vpc module in (.) format (e.g. module.root.aws_vpc.vpc_name.id) and also you can use
depends_on = [your vpc ] in your data resource declaration.
NOTE: I don't have required reputation here to suggest you these things as in comments, I may also loos my reputations here by answering you as a answer here.
Request: Please mention more details here, also paste your module tree structure for better understanding.
you can refer this link : https://www.terraform.io/docs/providers/aws/d/vpc.html
The data provider is actually only needed in cases in which you are referring to a resource that is created somewhere else
An example code that is correct.
provider "aws" {
region = "us-east-2"
}
data "aws_vpc" "example" {
filter {
name = "tag:Name"
values = ["TRIAL"]
}
}
output "show-me-vpc" {
value = data.aws_vpc.example.arn
}
Terraform registry AWS VPC example terraform-aws-vpc/examples/complete-vpc/main.tf has the code below which seems to me a circular dependency.
data "aws_security_group" "default" {
name = "default"
vpc_id = module.vpc.vpc_id
}
module "vpc" {
source = "../../"
name = "complete-example"
...
# VPC endpoint for SSM
enable_ssm_endpoint = true
ssm_endpoint_private_dns_enabled = true
ssm_endpoint_security_group_ids = [data.aws_security_group.default.id] # <-----
...
data.aws_security_group.default refers to "module.vpc.vpc_id" and module.vpc refers to "data.aws_security_group.default.id".
Please explain why this does not cause an error and how come module.vpc can refer to data.aws_security_group.default.id?
In the Terraform language, a module creates a separate namespace but it is not a node in the dependency graph. Instead, each of the module's Input Variables and Output Values are separate nodes in the dependency graph.
For that reason, this configuration contains the following dependencies:
The data.aws_security_group.default resource depends on module.vpc.vpc_id, which is specifically the output "vpc_id" block in that module, not the module as a whole.
The vpc module's variable "ssm_endpoint_security_group_ids" variable depends on the data.aws_security_group.default resource.
We can't see the inside of the vpc module in your question here, but the above is okay as long as there is no dependency connection between output "vpc_id" and variable "ssm_endpoint_security_group_ids" inside the module.
I'm assuming that such a connection does not exist, and so the evaluation order of objects here would be something like this:
aws_vpc.example in module.vpc is created (I just made up a name for this because it's not included in your question)
The output "vpc_id" in module.vpc is evaluated, referring to module.vpc.aws_vpc.example, and producing module.vpc.vpc_id.
data.aws_security_group.default in the root module is read, using the value of module.vpc.vpc_id.
The variable "ssm_endpoint_security_group_ids" for module.vpc is evaluated, referring to data.aws_security_group.default.
aws_vpc_endpoint.example in module.vpc is created, including a reference to var.ssm_endpoint_security_group_ids.
Notice that in all of the above I'm talking about objects in modules, not modules themselves. The modules serve only to create separate namespaces for objects, and then the separate objects themselves (which includes individual variable and output blocks) are what participate in the dependency graph.
Normally this design detail isn't visible: Terraform normally just uses it to potentially optimize concurrency by beginning work on part of a module before the whole module is ready to process. In some interesting cases like this though, you can also intentionally exploit this design so that an operation for the calling module can be explicitly sandwiched between two operations for the child module.
Another reason why we might make use of this capability is when two modules naturally depend on one another, such as in an experimental module I built that hides some of the tricky details of setting up VPC peering connections:
locals {
vpc_nets = {
us-west-2 = module.vpc_usw2
us-east-1 = module.vpc_use1
}
}
module "peering_usw2" {
source = "../../modules/peering-mesh"
region_vpc_networks = local.vpc_nets
other_region_connections = {
us-east-1 = module.peering_use1.outgoing_connection_ids
}
providers = {
aws = aws.usw2
}
}
module "peering_use1" {
source = "../../modules/peering-mesh"
region_vpc_networks = local.vpc_nets
other_region_connections = {
us-west-2 = module.peering_usw2.outgoing_connection_ids
}
providers = {
aws = aws.use1
}
}
(the above is just a relevant snippet from an example in the module repository.)
In the above case, the peering-mesh module is carefully designed to allow this mutual referencing, internally deciding for each pair of regional VPCs which one will be the peering initiator and which one will be the peering accepter. The outgoing_connection_ids output refers only to the aws_vpc_peering_connection resource and the aws_vpc_peering_connection_accepter refers only to var.other_region_connections, and so the result is a bunch of concurrent operations to create aws_vpc_peering_connection resources, followed by a bunch of concurrent operations to create aws_vpc_peering_connection_accepter resources.
I am tring to create a terraform configuration file to create an ec2 instance. I am using the variables.tf file to put all my variables. It works for most of the cases but there are two cases which I am not able to achieve. Any pointers is much appreciated.
1.using variable for aws instance name. Using var.service_name or "${service_name}" does not work.
resource "aws_instance" var.service_name {
ami = "ami-010fae13a16763bb4"
instance_type = "t2.micro"
.....
}
This post explains that resource name cannot be variables. But this is pretty old. Not sure if this is still the case.
2.Using variable inside another variable. For example I have connection parameters defined like this
connection {
host = "${aws_instance.terraformtest.public_ip}"
type = "ssh"
user = "ec2-user"
private_key = "${file("C:/Users/phani/Downloads/microservices.pem")}"
}
This works. I am using the ip generated from aws instance resource. But If i use it like this. It doesn't work
host = "${aws_instance.${service_name}.public_ip}"
Am I missing something or is there a workaround
Resource names in Terraform are required to be constants. In practice this usually isn't a problem, because a resource name only needs to be unique within a given module and so it shouldn't ever be necessary for a caller to customize what a resource is named in a child module. In the case where a particular resource is the primary object declared by a module, a common idiom is to name the resource "main", like resource "aws_instance" "main".
In situations where you need to declare several instances whose definitions share a common configuration, you can use for_each or count to produce multiple instances from a same resource block. In that case, the resource addresses include an additional "index" component, like aws_instance.example["foo"] or aws_instance.example[0], where the index can be a variable to dynamically select one of the instances produced by a single resource block.
terraform has adjusted its authorization
in main.tf [for sql config] I now have:
resource "google_sql_database_instance" "master" {
name = "${random_id.id.hex}-master"
region = "${var.region}"
database_version = "POSTGRES_9_6"
# allow direct access from work machines
ip_configuration {
authorized_networks = "${var.authorized_networks}"
require_ssl = "${var.sql_require_ssl}"
ipv4_enabled = true
}
}
where
in variables.tf I have
variable "authorized_networks" {
description = "The networks that can connect to cloudsql"
type = "list"
default = [
{
name = "work"
value = "xxx.xxx.xx.xxx/32"
}
]
}
where xxx.xxx.xx.xxx is the ip address I would like to allow. However, I prefer not to put this in my variables.tf file, but rather in a non-source controlled .tfvars file.
for variables that have a simple value, this is easy, but it is not clear to me how to do it with the nested structure. Replacing xxx.xxx.xx.xxx by a variable [e.g. var.work_ip] leads to an error
variables may not be used here
any insights?
If you omit the default argument in your main configuration altogether, you will mark variable "authorized_networks" as a required input variable, which Terraform will then check to ensure that it is set by the caller.
If this is a root module variable, then you can provide the value for it in a .tfvars file using the following syntax:
authorized_networks = [
{
name = "work"
value = "xxx.xxx.xx.xxx/32"
}
]
If this file is being generated programmatically by some wrapping automation around Terraform, you can also write it into a .tfvars.json file and use JSON syntax, which is often easier to construct robustly in other languages:
{
"authorized_networks": [
{
"name": "work",
"value": "xxx.xxx.xx.xxx/32"
}
]
}
You can either specify this file explicitly on the command line using the -var-file option, or you can give it a name ending in .auto.tfvars or .auto.tfvars.json in the current working directory when you run Terraform and Terraform will then find and load it automatically.
A common reason to keep something out of version control is because it's a dynamic setting configured elsewhere in the broader system rather than a value fixed in version control. If that is true here, then an alternative strategy is to save that setting in a configuration data store that Terraform is able to access via data sources and then write your Terraform configuration to retrieve that setting directly from the place where it is published.
For example, if the network you are modelling here were a Google Cloud Platform subnetwork, and it has either a fixed name or one that can be derived systematically in Terraform, you could retrieve this setting using the google_compute_subnetwork data source:
data "google_compute_subnetwork" "work" {
name = "work"
}
Elsewhere in configuration, you can then use data.google_compute_subnetwork.work.ip_cidr_range to access the CIDR block definition for this network.
The major Terraform providers have a wide variety of data sources like this, including ones that retrieve specific first-class objects from the target platform and also more generic ones that access configuration stores like AWS Systems Manager Parameter Store or HashiCorp Consul. Accessing the necessary information directly or publishing it "online" in a configuration store can be helpful in a larger system to efficiently integrate subsystems.