How to configure the Juju model of COS¶

The COS Terraform module creates a Juju model named cos by default. Use the model variable to customize the configuration of the module-managed model, or target an existing model with a UUID. Think of model configuration as “would I do this with the Juju CLI?” If not, then doing this with Terraform should be conducted in a staging or dev environment and not attempted in a production-like environment.

Set a custom model name and configuration¶

Set the model variable with the desired name and any Juju model configuration, for example:

module "cos" {
  source = "git::https://github.com/canonical/observability-stack.git//terraform/cos"

  model = {
    name = "cos-production"
    config = {
      logging-config = "<root>=WARNING; unit=DEBUG"
    }
  }
}

After deploying COS, you may want to update the module-managed model’s configuration. Just update the model’s config and apply. Review the common configuration mistakes before continuing.

Deploy into an existing model¶

To deploy COS into a model that already exists, provide its UUID via model.uuid:

module "cos" {
  source = "git::https://github.com/canonical/observability-stack.git//terraform/cos"

  model = {
    uuid = "82d8c989-3087-416b-8ff2-d94ede266035"
  }
}

To retrieve the UUID of an existing model, run:

juju models --format json | jq -r '.models[] | select(.name | contains("my-cos-model"))["model-uuid"]'

Common configuration mistakes¶

Creating a model which already exists¶

If you set the model.name to the same name as an existing model, then Juju returns a client error because it cannot create the model:

module.cos.juju_model.cos[0]: Creating...
╷
│ Error: Client Error
│ 
│   with module.cos.juju_model.cos[0],
│   on .terraform/modules/cos/terraform/cos/model.tf line 3, in resource "juju_model" "cos":
│    3: resource "juju_model" "cos" {
│ 
│ Unable to create model "\"my-cos-model\"", got error: failed to open kubernetes client: annotations map[controller.juju.is/id:7c1aed20-86bf-4853-8609-62a08f25bca6 model.juju.is/id:82d8c989-3087-416b-8ff2-d94ede266035] for namespace "my-cos-model"
│ not valid must include map[controller.juju.is/id:7c1aed20-86bf-4853-8609-62a08f25bca6 model.juju.is/id:2c0550ed-7129-47bb-884b-1234f56f308b] (not valid)

Choose a new model name or remove the existing one to proceed.

Switching Juju models post-deployment¶

The Juju Terraform provider translates state changes into Juju API calls. There is no guarantee that arbitrary state transitions, such as:

switching between a module-managed model and a pre-existing one
changing the name of the module-managed model
updating the model.uuid

will converge without manual intervention.