provider/docker: Add support for multiple docker_image pull_triggers

[hmcgonig]

Terraform Version

0.7.13

Affected Resource(s)

Please list the resources as a list, for example:

• docker_image

Terraform Configuration Files

data "docker_registry_image" "elasticsearch" {
  name = "elasticsearch:latest"
}

resource "docker_image" "elasticsearch" {
  keep_locally = true
  name = "${data.docker_registry_image.elasticsearch.name}"
  pull_trigger = "${data.docker_registry_image.elasticsearch.sha256_digest}"
}

Currently, the above will pull the elasticsearch image into every host in my docker swarm cluster. In my environment I have found that when scaling up my docker swarm, I have no way to trigger another docker_image.elasticsearch pull so that my new swarm node gets an ES image. Currently, the workaround is that I would have to taint this resource to get it on my new node. Alternatively I can interpolate the cluster size and sha256 together.

I'm proposing support for something like this:

data "docker_registry_image" "elasticsearch" {
  name = "elasticsearch:latest"
}

resource "docker_image" "elasticsearch" {
  keep_locally = true
  name = "${data.docker_registry_image.elasticsearch.name}"
  pull_triggers = ["${data.docker_registry_image.elasticsearch.sha256_digest}", "${var.swarm_size}"]
}

So pull_trigger becomes a list called pull_triggers so that image pulls can be invoked by state changes other than just sha changes.

The other change required is that currently when pulling images, the docker provider first checks to see which images are already pulled, then if the image you want is not pulled, it pulls it. When using swarm, while setting up a new swarm host, terraform will not pull existing images onto new hosts, because those same images already exist on some nodes of the cluster already. The simplest fix I can see is to remove this check that sees if an image is already pulled. Pulling an image that you already have just results in a no-op with the side-effect that new swarm hosts will now also download the image as needed.

Later today I'll be throwing together a PR for this enhancement since it should be a very easy change, but I just wanted to get an issue out there for tracking. Thanks!

[stack72]

Closed via #10845

[ghost]

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