如何在不连接AWS的情况下从Terraform配置生成执行计划？

Question

I'm writing a unit test for a Terraform module, and I would like to confirm that the module produces the execution plan that I expect. However, connecting to Amazon within a test would take too long and require too much configuration of the continuous integration server.

How can I use terraform plan to generate an execution plan from my configuration that assumes that no resources exist?

Answer 1

I've been considering something similar for a testing framework around Terraform modules and have previously used Moto for mocking Boto calls in Python.

Moto works by monkey patching calls to AWS so only works natively with Python. However it does provide the mocked backend as a server running on Flask to be used in a stand alone mode.

That said, I've just tried it with Terraform and while plan s seem to work okay a very basic configuration being applied led to this error:

* aws_instance.web: Error launching source instance: SerializationError: failed decoding EC2 Query response
caused by: parsing time "2015-01-01T00:00:00+0000" as "2006-01-02T15:04:05Z": cannot parse "+0000" as "Z"

I then happened to notice that plans complete fine even when the Moto server isn't running and I'm just using a non existent local endpoint in the AWS provider .

As such, if you just need plans then you should be able to do this by adding an endpoint block that points to localhost like this:

provider "aws" {
  skip_credentials_validation = true
  max_retries = 1
  skip_metadata_api_check = true
  access_key = "a"
  secret_key = "a"
  region = "us-west-2"

  endpoints {
    ec2 = "http://127.0.0.1:5000/"
  }
}


resource "aws_instance" "web" {
    ami = "ami-123456"
    instance_type = "t2.micro"
    tags {
        Name = "HelloWorld"
    }
}

How you inject that endpoint block in for testing and not for real world usage is probably another question and would need more information in how your tests are being constructed.

Answer 2

Does terraform plan -refresh=false do what you want?

I use it to do a "fast plan", without taking the time to refresh the status of all the AWS resources. Not sure if it actually connects to AWS to do that though.

If you're using a more complicated remote-state setup and that's the part you don't want to configure - you could also try adding an empty tfstate file and pointing to that with the -state option.