# Stack Mixins

_Advanced_

Mixins are reusable snippets of configurations (like regions, tags, etc) included in stack configurations to avoid repetition and enhance modularity. They allow for defining common settings, variables, or configurations once and applying them efficiently across various stacks.

:::important
Mixins are treated the same as all other imports in Atmos, with no special handling or technical distinction.
:::

## Use-cases

Here are some use-cases for when to use mixins.

### Mixins by Region

Mixins organized by region will make it very easy to configure where a stack is deployed by simply changing the imported mixin.

Consider naming them after the canonical region name for the cloud provider you're using.

For example, here's what it would look like for AWS. Let's name this file `mixins/region/us-east-1.yaml`.
Now, anytime we want a Parent Stack deployed in the `us-east-1` region, we just need to specify this import, and we'll automatically inherit all the settings for that region.

For example, let's define a mixin with the defaults for operating in the `us-east-1` region:

```yaml title="mixins/region/us-east-1.yaml"
vars:
  region: us-east-1   # the canonical cloud region
  availability_zones: # the designated availability zones to use in this region
  - us-east-1a
  - us-east-1b
```

Then we can use this mixin, anytime we deploy in `us-east-1` to ensure we conform to the organization's standards.

```yaml title="stacks/prod/network.yaml"
imports:
- mixins/region/us-east-1

terraform:
  components:
    vpc:
    # ...
```

### Mixins by Stage

Provide the default settings for operating in a particular stage (e.g. Dev, Staging, Prod) to enforce consistency.

For example, let's define the stage name and required tags for production in the mixin file named `mixins/stage/prod.yaml`

```yaml title="mixins/stage/prod.yaml"
vars:
  stage: prod
  tags:
    CostCenter: 12345
```

Now, anytime we want to provision a parent stack in production, we'll want to add this to the imports:

```yaml title="stacks/prod/backing-services.yaml"
imports:
- mixins/stage/prod

terraform:
  components:
    rds-cluster:
    # ...
```

:::tip Use Mixins for Naming Conventions
This simple example highlights a simple fix for one of the most common issues in enterprise organizations: naming inconsistency.
Using a mixin is a great way for organizations ensure naming conventions are followed consistently.

For example, there are many ways developers will define `production`.

- e.g. `prd`
- e.g. `prod`
- e.g. `production`
- e.g. `Production`
- e.g. `Prod`
- e.g. `PROD`
- etc
  :::

To avoid this situation, use the mixin `mixins/stage/prod` and always use the appropriate naming convention.

Mixins are really just a [Design Pattern](/design-patterns/component-catalog/with-mixins) for [`imports`](/stacks/imports) that uses [inheritance](/howto/inheritance) to alter the Stack configuration in some deliberate way.
Learn Design Pattern[Read more](/design-patterns/component-catalog/with-mixins)