terraform planning a portion of your resources

When running around with Terraform it's pretty annoying to wait for a full plan if you're only working on a few independent resources. For larger projects this can eat up several minutes of time.

A quick way to get around this "only in extreme circumstances" (according to Hashicorp) would be to specify a target in the command. This will focus solely on that resource and its given dependency graph.

Example scenario

We have 2 files (config.tf, templates/config.yml.tpl) with 2 resources (data, local_file).

Structure

Tree:

terraform/
    config.tf
    templates/
        config.yml.tpl

# config.tf
data "template_file" "config_yml" {
    template = "${file("${path.module}/templates/config.yml.tpl")}"
    vars = {
        region = provider.region
        stage = terraform.workspace
    }
}

resource "local_file" "local_config" {
    content = data.template_file.config_yml.rendered
    filename = "../my-config.yml"
}

# templates/config.yml.tpl

config:
    region: ${region}
    stage: ${stage}

Running a TF plan on this

Terraform plan typically takes everything in your directory, instead we can take just the config.tf by specifying the resource block.

terraform plan -target local_file.local_config