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Set of Python-based CLI tools for working with Terraform configurations

Project description

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Terrawrap
=========

Set of Python-based CLI tools for working with Terraform configurations
in bulk

About Amplify
-------------

Amplify builds innovative and compelling digital educational products
that empower teachers and students across the country. We have a long
history as the leading innovator in K-12 education - and have been
described as the best tech company in education and the best education
company in tech. While others try to shrink the learning experience into
the technology, we use technology to expand what is possible in real
classrooms with real students and teachers.

Learn more at https://www.amplify.com

Table of Contents
-----------------

- `Features <#features>`__

- `Goals <#goals>`__

- `Getting Started <#getting-started>`__

- `Prerequisites <#prerequisites>`__
- `Installing/Building <#installingbuilding>`__
- `Running Tests <#running-tests>`__

- `Configuration <#configuration>`__

- `.tf\_wrapper <#tf_wrapper>`__
- `Autovars <#autovars>`__
- `Terraform S3 Remote State <#terraform-s3-remote-state>`__

- `Commands <#commands>`__

- `tf <#tf>`__
- `plan\_check <#plan_check>`__

Features
--------

1. ``auto.tfvars`` inheritance. Terrawrap makes it easier to share
variables between Terraform directories through inheritance of
``auto.tfvars`` files.

2. Remote S3 backend generation. Terrawrap makes it easier to work with
AWS S3 remote state backends by generating configuration for them.

3. Repository level plan/apply. Terrawrap provides commands for running
plan/apply recursively on a entire repository at once.

Goals
-----

1. Make Terraform DRY for large organizations. A Terraform best
practices is to break up Terraform configs into many small state
files. This leads to an explosion in boilerplate code when using
Terraform in large organizations with 100s of state files. Terrawrap
reduces some boilerplate code by providing ``auto.tfvars``
inheritance and generating backend configurations.

2. Make Terraform code easier to manage. Terraform only runs commands on
a single directory at a time. This makes working with hundreds of
terraform directories/state files hard. Terrawrap provides utilities
for running commands against an entire repository at once instead of
one directory at a time.

3. All Terraform code should be valid Terraform. Any Terraform code used
with Terrawrap should be runnable with Terraform by itself without
the wrapper. Terrawrap does not provide any new syntax.

4. Terrawrap is not a code generator (except when generating terraform
backends). Generated code is harder to read and understand. Code
generators tend to lead to leaky abstractions that can be more
trouble than they are worth.

Getting Started
---------------

Prerequisites
~~~~~~~~~~~~~

Terrawrap requires Python 3.6.0 or higher to run.

Installing
~~~~~~~~~~

This package can be installed using ``pip``

.. code:: sh

pip install terrawrap

You should now be able to use the ``tf`` command.

Building From Source
--------------------

For development, ``tox>=2.9.1`` is recommended.

Running Tests
~~~~~~~~~~~~~

Terrawrap uses ``tox``. You will need to install tox with
``pip install tox``. Running ``tox`` will automatically execute linters
as well as the unit tests.

You can also run them individually with the ``-e`` argument.

For example, ``tox -e py37-unit`` will run the unit tests for python 3.7

To see all the available options, run ``tox -l``.

Configuration
-------------

.tf\_wrapper
~~~~~~~~~~~~

Terrawrap can be configured via a ``.tf_wrapper`` file. The wrapper will
walk the provided configuration path and look for ``.tf_wrapper`` files.
The files are merged in the order that they are discovered. Consider the
below example:

.. code:: text

foo
├── bar
│   └── .tf_wrapper
└── .tf_wrapper

If there are conflicting configurations between those two
``.tf_wrapper`` files, the ``.tf_wrapper`` file in ``foo/bar`` will win.

The following options are supported in ``.tf_wrapper``:

.. code:: yaml

configure_backend: True # If true, automatically configure Terraform backends.
pipeline_check: True # If true, require this directory to be in a pipeline file.

envvars:
<NAME_OF_ENVVAR>:
source: # The source of the envvar. Currently only `ssm` is supported.
path: # If the source of the envvar is `ssm`, the SSM Parameter Store path to lookup the value of the environment variable from.

Autovars
~~~~~~~~

Terrawrap automatically adds ``-var-file`` arguments to any terraform
command by scanning for ``*.auto.tfvars`` files in the directory
structure.

For example, the following command ``tf config/foo/bar apply`` with the
following directory structure:

.. code:: text

config
├── foo
|   └── bar
|   │ ├── baz.tf
|   │ └── bar.auto.tfvars
|   └── foo.auto.tfvars
└── config.auto.tfvars

will generate the following command:

.. code:: bash

terraform apply -var-file config/config.auto.tfvars \
-var-file foo.auto.tfvars \
-var-file bar.auto.tfvars

Terraform S3 Remote State
~~~~~~~~~~~~~~~~~~~~~~~~~

Terrawrap supports automatically configuring S3 remote backends. It will
inject the appropriate ``-backend-config`` args when running ``init``

For example, the following Terrawrap command ``tf config/foo/bar init``
will generate a Terraform command like

.. code:: bash

terraform init -reconfigure \
-backend-config=dynamodb_table=<lock table name> \
-backend-config=encrypt=true \
-backend-config=key=config/foo/bar.tfstate \
-backend-config=region=<region name> \
-backend-config=bucket=<state bucket name> \
-backend-config=skip_get_ec2_platforms=true \
-backend-config=skip_region_validation=true \
-backend-config=skip_credentials_validation=true

Terrawrap configures the backend by looking for ``*.auto.tfvars`` files
in the directory structure. The following variables will be used to
configure S3 backends

+----------------------------+---------------------+--------------------------------------------------------------------------+
| Variable Name | Default value | Purpose |
+============================+=====================+==========================================================================+
| terraform\_lock\_table | terraform-locking | Name of DynamoDB lock table to use with S3 backend |
+----------------------------+---------------------+--------------------------------------------------------------------------+
| terraform\_state\_bucket | | Name of AWS S3 bucket that will hold Terraform state files |
+----------------------------+---------------------+--------------------------------------------------------------------------+
| region | | AWS Region that S3 state bucket and DynamoDB lock table are located in |
+----------------------------+---------------------+--------------------------------------------------------------------------+

The S3 state file key name is generated from the directory name being
used to run the terraform command. For example,
``tf config/foo/bar init`` uses a state file in the
``config/foo/bar.tfstate`` key in S3

The value of the assume role ARN is read from ``*.auto.tfvars`` files in
the directory structure. Terrawrap will look for a variable named
``tf_aws_provider_role``

Commands
--------

tf
~~

``tf <directory> <terraform command>`` runs a terraform command for a
given directory that contains ``*.tf`` files. Terrawrap automatically
includes autovars as described above when running the given command. Any
Terraform command is supported

plan\_check
~~~~~~~~~~~

``plan_check <directory>`` runs ``terraform plan`` recursively for all
child directories starting at the given directory. ``plan_check`` uses
``git`` to identify which files have changed compared with the
``master`` branch. It will then run ``plan`` on any directory that
contains ``tf`` files with the following criteria 1. A directory that
has files that changed 2. A directory that is symlinked to a directory
that has files changed 3. A directory with symlinked files that are
linked to files that changed 4. A directory that that uses a Terraform
module whose source changed 5. A directory with Terraform files that
refer to an autovar file that changed

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