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Terraform 0.14 Adds a New Concise Diff Format to Terraform Plans

Terraform 0.14 now features a new concise diff renderer that makes it easier to see changes for any Terraform plan.

Nov 02 2020Alisdair McDiarmid, Petros Kolyvas

HashiCorp Terraform 0.14 includes a new, experimental, on-by-default, concise diff renderer. This small but significant new behavior is designed to help practitioners quickly understand what changes Terraform is about to make to existing infrastructure.

Background

Terraform 0.12 introduced a new plan file format and structural diff renderer, which was a significant change from 0.11. Most notably, for updated resources, Terraform moved from showing only the changed attribute path/values, to showing the entire resource with changed values prefixed with ~.

For plans which slightly change existing resources, this can result in very large diffs which make it difficult to reason about the actual changes.

Diff Renderer Design

The diff renderer used by terraform plan, terraform apply, and terraform show <planfile> has been updated to hide unchanged and irrelevant fields. This means:

Always show all identifying fields, initially defined as id, name, and tags, even if unchanged
Only show changed, added, or removed primitive values: string, number, or bool
Only show added or removed elements in unordered collections and structural types: map, set, and object
Show added or removed elements with up to two contextual unchanged elements for sequence types: list and tuple
Only show added or removed nested blocks, or blocks with changed attributes

If any attributes, collection elements, or blocks are hidden, a count will be kept and displayed at the end of the parent scope. This ensures that the diff is clearly only displaying a subset of the resource.

Diff Rendering Details

Changed primitive values will render as before: prefixed with a ~, and showing the old and new value. Any hidden attributes will be counted, and the total displayed at the end of the resource:

~ attribute_name   = "old value" -> "new value"
  # (12 unchanged attributes hidden)

Unordered collections (sets or maps) with added or removed elements will use the same approach:

~ regions = [
    - "us-east-1",
    - "us-west-2",
    + "eu-west-1",
    + "eu-west-2",
      # (1 unchanged element hidden)
  ]

Sequences (lists or tuples) will display context around changes:

~ words     = [
      # (3 unchanged elements hidden)
    - "delta",
    + "data",
      "echo",
      # (5 unchanged elements hidden)
      "kilo",
    - "Lima",
    + "London",
      "Mike",
      " (13 unchanged elements hidden)
  ]

Any nested blocks for a resource that are unchanged will also be counted and the total displayed:

# (3 unchanged blocks hidden)

When color is enabled, these hidden value counts will be displayed in a lower-contrast color.

Diff Examples

Changes to attributes:

  # test_resource.foo will be updated in-place
  ~ resource "test_resource" "foo" {
        id       = "foo_123"
      ~ checksum = 28987129 -> (known after apply)
      - mode     = "test" -> null
        name     = "Foo Test"
        tags     = []
      ~ totals   = {
          - "bar" = 5 -> null
          + "baz" = 5
              # (2 unchanged elements hidden)
        }
      ~ values   = [
          - "alpha",
          - "gamma",
          + "alpaca",
          + "goblin",
          + "zephyr",
            # (23 unchanged elements hidden)
        ]
        # (5 unchanged attributes hidden)
 
        # (3 unchanged blocks hidden)
    }

Adding a new block:

  # test_resource.foo will be updated in-place
  ~ resource "test_resource" "foo" {
        id       = "foo_123"
      ~ checksum = 28987129 -> (known after apply)
        name     = "Foo Test"
        tags     = []
        # (8 unchanged attributes hidden)
 
      + sub_item {
          + identifier = "bar"
          + size       = 4
          + type       = "whatever"
        }
        # (3 unchanged blocks hidden)
    }

»Getting Started

We have many resources available for 0.14 for new and existing users. To learn more about the new functionality of 0.14 you can:

Review the documentation
Try our HashiCorp Learn tutorials which have been updated for Terraform 0.14
Lock and Upgrade Provider Versions
Protect Sensitive Input Variables

To get started using 0.14:

Download the Terraform 0.14 release.
If you are upgrading from a previous release, read the upgrade guide to learn how to adopt Terraform’s new features.

For more details, please see the full changelog. This release also includes a number of code contributions from the community and wouldn't have been possible without all of the great community feedback we've received via GitHub issues and elsewhere. Thank you!

HashiCorp Terraform 0.14 is the next step on our way to solidifying the Terraform ecosystem and empowering collaborative workflows at organizations of all sizes. You can download Terraform 0.14 here and sign up for a Terraform Cloud account here.

Terraform 0.14 Adds a New Concise Diff Format to Terraform Plans

Background

Diff Renderer Design

Diff Rendering Details

Diff Examples

»Getting Started

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