Support to create container without docker_image resource

[suzuki-shunsuke]

I try using Discussion.

---

Currently, when we create a docker_container resource, an image ID is required so docker_image resource is used to convert an image name into an image ID.

e.g.

resource "docker_container" "ubuntu" {
  name  = "foo"
  image = docker_image.ubuntu.latest
}

# Find the latest Ubuntu precise image.
resource "docker_image" "ubuntu" {
  name = "ubuntu:precise"
}

https://registry.terraform.io/providers/kreuzwerker/docker/latest/docs/resources/container#image

image - (Required, string) The ID of the image to back this container.
The easiest way to get this value is to use the docker_image resource as is shown in the example above.

But in this case the motivation to use docker_image resource isn't to manage the image with Terraform but just to create a container.
Using docker_image resource means the image is managed with Terraform.
So I feel this gap raises undesirable situation.
Even if the container is updated, we don't want to delete an old image.
Of course I know the docker_image's keep_locally attribute exists to prevent the old image from being removed,
but I wonder this behaviour isn't natural for Terraform and maybe this is the root cause of some problems.

For example, recently I encounter some problems regarding to docker_image resource.

#178 (comment)
#178 (comment)

If we want to manage the image with Terraform, docker_image resource is good,
but otherwise I wonder we should create a container without docker_image resource.

That is, we should be able to create a container by specifying image name, image digest etc.

I'm not confident that my idea is correct.

[suzuki-shunsuke]

Maybe adding an attribute latest to docker_registry_image data source and using it instead of docker_image.latest is one of simple solution. 🤔

[suzuki-shunsuke]

No. In that case docker_registry_image.latest is updated when the remote image is updated.
In some cases It isn't desirable.

[suzuki-shunsuke]

No. In that case docker_registry_image.latest is updated when the remote image is updated.
In some cases It isn't desirable.

But in case docker_image.pull_triggers is used, this isn't a problem.

[suzuki-shunsuke]

(BTW, I don't know why pull_triggers is required instead of pull_trigger.) hashicorp/terraform-provider-docker@0a75a72

[suzuki-shunsuke]

Hmm. Maybe this is wrong.
The target of docker_registry_image data source isn't a local image but an image on a registry, and no image is pulled.
docker_registry_image doesn't get the image ID by API.

[suzuki-shunsuke]

The problem is there are many formats which represent an image.
It is difficult to import a container and suppress change.

[suzuki-shunsuke]

📝

$ docker inspect 2c5538c76508 | grep "Image"
        "Image": "sha256:7731472c3f2a25edbb9c085c78f42ec71259f2b83485aa60648276d408865839",
            "Image": "alpine:3.13.0",

• .Image: image ID
• .Config.Image

[suzuki-shunsuke]

• image_config
  • id
  • name
  • digest
  • check_remote_digest
  • check_id_changed

---

• image_config
  • id

---

• image_config
  • digest

---

• image_config
  • name
  • check_remote_digest

---

• image_config
  • name
  • check_id_changed

---

• image_config
  • name