Terraform Provider Multiverse

This provider is similar to Custom Resources in AWS CloudFormation. You can write a script that will be used to create, update or destroy external resources that are not supported by Terraform.

You can use this provider instead of writing your own Terraform Custom Provider in golang, just write your logic in any language you prefer (python, node, java) and use it with this provider.

Maintainers

This provider plugin is maintained by the MobFox DevOps team at MobFox.

Requirements

• Terraform 0.10.x
• Go 1.8 (to build the provider plugin)

Building The Provider

Clone repository to: $GOPATH/src/github.com/mobfox/terraform-provider-multiverse

$ mkdir -p $GOPATH/src/github.com/mobfox; cd $GOPATH/src/github.com/mobfox
$ git clone git@github.com:mobfox/terraform-provider-multiverse.git

Enter the provider directory and build the provider

$ cd $GOPATH/src/github.com/mobfox/terraform-provider-multiverse
$ make build

Using the provider

Check the examples Here an example of Spotinst Multai Load Balancer TargetSet

provider "multiverse" {}

resource "multiverse_custom_resource" "spotinst_targetset_and_rules" {
  executor = "python3"
  script = "spotinst_mlb_targetset.py"
  id_key = "id"
  data = <<JSON
{
  "name": "test-terraform-test",
  "mlb_id": "lb-123",
  "mlb_deployment_id": "dp-123",
  "mlb_listener_ids": ["ls-123", "ls-456"],
  "test_group_callback_fqdn": "test.fqdn.com",
  "control_group_callback_fqdn": "control.fqdn.com"
}
JSON
}

• When you run terraform apply the resource will be created / updated
• When you run terraform destroy the resource will be destroyed

Attributes

Input

• executor (string) could be anything like python, bash, sh, node, java, awscli ... etc
• script (string) the path to your script or program to run, the script must exit with code 0 and return a valid json
• id_key (string) the key of returned result to be used as id
• data (string) must be a valid json payload

Output

• resource (map[string]) the output of your script must be a valid json with all keys of type string in the form {"key":"value"}

Referencing in TF template

This an example how to reference the resource and access its attributes

Let's say your script returned the following result

{
  "id": "my-123",
  "name": "my-resource",
  "capacity": "20g"
}

then the resource in TF will have these attributes

id = "my-123"
resource = {
  name = "my-resource"
  capacity = "20g"
  id = "my-123"
}

you can access these attributes using variables

${multiverse_custom_resource.my_custom_resource.id} # accessing id
${multiverse_custom_resource.my_custom_resource.resource["name"]}
${multiverse_custom_resource.my_custom_resource.resource["capacity"]}

Why the attribute data is stringified JSON?

This will give you flexibility in passing your arguments with mixed types We couldn't define a with generic mixed types, if we used map then all attributes have to be explicitly defined in the schema or all its attributes have the same type

Writing a script

Your script must be able to handle the TF event and the JSON payload data

• event : will have one of these create, read, delete, update
• data is passed via stdin

and your script should look something like this

import sys
import json
...

def handler(event, data):
   data_as_json = json.loads(data)
   if event == "create":
        ...
        
   elif event == "read":
        ...
        
   elif event == "update":
        ...
        
   elif event == "delete":
        ... 
   
def read_data():
    data = ''
    for line in sys.stdin:
        data += line

    return data
   
if __name__ == '__main__':
    context = read_data()
    print(json.dumps(handler(sys.argv[1], context)))

To test your script before using in TF

echo "{\"key\":\"value\"}" | python3 my_resource.py create

Developing the Provider

If you wish to work on the provider, you'll first need Go installed on your machine (version 1.8+ is required). You'll also need to correctly setup a GOPATH, as well as adding $GOPATH/bin to your $PATH.

To compile the provider, run make build. This will build the provider and put the provider binary in the $GOPATH/bin directory.

$ make bin
...
$ $GOPATH/bin/terraform-provider-multiverse
...

In order to test the provider, you can simply run make test.

$ make test

Feel free to contribute!