Astro
Astro is a tool for managing multiple Terraform executions as a single command.
Features:
- Declarative configuration for modules to execute
- Dependencies between modules
- Fast, concurrent executions of Terraform operations
- Safe Terraform upgrades and state file migrations
NOTE: Astro is currently experimental.
Getting started
Installation
Install Astro using go get (Go >1.12 required):
GO111MODULE=on go get github.com/uber/astro/astro/cli/astro
This will install a binary called astro in your $GOPATH/bin.
Alternatively, you can download precompiled binaries from the Github releases page.
Note that from version 0.6.0 tvm, a tool to download and install specific versions of Terraform for your platforms,
is packaged together with astro.
Configuration
Astro looks for a configuration file called astro.yaml in the current or parent directories. It is recommended to place this file in the same top-level directory of your project where the Terraform code exists (e.g. terraform/astro.yaml).
An example astro configuration could look like:
---
terraform:
version: 0.11.7
hooks:
startup:
- command: assume-role --role terraform
set_env: true
modules:
- name: app
path: core/app
deps:
- module: users
- module: vpc
remote:
backend_config:
bucket: acme-terraform-states
key: "{{.aws_region}}/app-{{.environment}}.tfstate"
region: us-east-1
variables:
- name: region
- name: environment
values: [dev, prod]
- name: database
path: core/database
remote:
backend_config:
bucket: acme-terraform-states
key: "{{.aws_region}}/database-{{.environment}}.tfstate"
region: us-east-1
variables:
- name: region
- name: environment
values: [dev, prod]
- name: mgmt
path: core/mgmt
deps:
- module: vpc
variables:
environment: mgmt # depends on vpc/mgmt
remote:
backend_config:
bucket: acme-terraform-states
key: "{{.aws_region}}/mgmt-{{.environment}}.tfstate"
region: us-east-1
variables:
- name: region
- name: users
path: core/users
remote:
backend_config:
bucket: acme-terraform-states
key: global/users
region: us-east-1
- name: vpc
path: core/vpc
remote:
backend_config:
bucket: acme-terraform-states
key: "{{.aws_region}}/vpc-{{.environment}}.tfstate"
region: us-east-1
variables:
- name: region
- name: environment
values: [mgmt, dev, prod]
Planning
You can run a plan across all modules by doing:
astro plan --region us-east-1
--region in this example is one of the variables defined in the module configuration above with no predefined value, so it must be provided at the command line.
Astro will show the results of the plan for each execution:
> astro plan --region us-east-1
users: OK No changes (7s)
vpc-mgmt-us-east-1: OK No changes (15s)
vpc-dev-us-east-1: OK No changes (31s)
vpc-prod-us-east-1: OK No changes (28s)
database-dev-us-east-1: OK No changes (9s)
database-prod-us-east-1: OK No changes (10s)
app-dev-us-east-1: OK No changes (10s)
app-prod-us-east-1: OK No changes (11s)
mgmt-us-east-1: OK No changes (43s)
>
If there is a change, the plan will be shown, e.g.:
> astro plan --region us-east-1 --modules app
app-dev-us-east-1: OK Changes (10s)
~ module.app.aws_s3_bucket.app-data
versioning.0.enabled: "false" => "true"
app-prod-us-east-1: OK Changes (11s)
~ module.app.aws_s3_bucket.app-data
versioning.0.enabled: "false" => "true"
>
Upgrading
Upgrading Terraform is as easy as changing the version in the config, e.g.:
diff --git a/terraform/astro.yaml b/terraform/astro.yaml
index 5725a36d..c0ef720f 100644
--- a/terraform/astro.yaml
+++ b/terraform/astro.yaml
@@ -1,7 +1,7 @@
---
terraform:
- version: 0.10.5
+ version: 0.11.7
modules:
- name: app
Astro will automatically download the new version when it needs it next.
Detaching from the remote
Older versions of Terraform had the ability to disable the remote state, which was useful for performing safe upgrades or migrations.
Astro restores this ability using the --detach command to plan, e.g.:
astro plan --detach
This will create a session directory with a sandbox containing a copy (hard links) of the Terraform code, along with a local copy of the state file:
> ls terraform/.astro/01CGC80C81CJFPFCCM0F1FRKDJ/app/sandbox/core/app/terraform.tfstate
terraform/.astro/01CGC80C81CJFPFCCM0F1FRKDJ/app/sandbox/core/app/terraform.tfstate
If you need to test anything, you can change directory within the sandbox without affecting the remote.
Hooks
Astro can run run external commands both at startup or before the execution of a module. If set_env is true, Astro will parse command
output for NAME=value pairs, and set those as environment values.
This can be useful, for example, when using an assume-role script to assume an AWS role that requires MFA authentication. If the script outputs
AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY and AWS_SESSION_TOKEN to standard output, then it can be used as a startup hook by Astro to
transparently change role before running Terraform.
Use cases
Dynamic environments
When running a terraform plan or terraform apply, you can specify custom variables at the command line (using -var foo=bar). This can be used to dynamically deploy to a particular environment, or region, for example.
Astro allows you to specify these variables at runtime, or filter a set of predefined ones.
In the example configuration above, the "app" and "database" modules are deployed to two different environments ("dev" and "prod") by invoking Terraform with different -var environment=<value> flags set.
What is happening behind the scenes is the module configuration generates a list of "executions", which is a Cartesian product of each set of possible variable values, plus the user-provided values at run time.
Each execution is then run in parallel, taking into considerations dependencies that modules may have on one another.
Targeted deploys
Given a list of predefined environments, the user can "filter" which executions are run. For example, the following would run only the executions with enviroment=dev:
astro plan --enviroment dev
The result would be:
> astro plan --region us-east-1 --environment dev
vpc-dev-us-east-1: OK No changes (31s)
database-dev-us-east-1: OK No changes (9s)
app-dev-us-east-1: OK No changes (10s)
>
Remapping CLI flags
Astro is meant to be used every day by operators. If your Terraform variable names are long-winded to type at the CLI, you can remap them to something simpler. For example, instead of typing --environment dev, you may wish to shorten this to --env dev.
You can specify a flags: block in your project configuration, like:
flags:
environment:
name: env
description: Environment to deploy to
This will remap the "environment" Terraform variable to --env on the astro command line. You can also specify a description that will show up in the --help text.