Separate stateful infrastructure with Serverless Compose
Tags: serverless, aws, cloud, tutorial
Published: 2022-07-05 08:10:12

One of the most significant benefits of serverless is that the development teams can fully own and manage all of their infrastructure themself. Keeping all of that infrastructure in the same CloudFormation stack can sometimes be troublesome however, and there are many reasons why you might consider having parts of it in a separate stack. A common approach is to keep stateful infrastructure, such as your DynamoDB tables or S3 buckets, in one stack, and stateless infrastructure, such as your Lambda functions or API gateways, in another. This way, you can more freely update or even tear down the stack that's naturally often changing while not risking affecting the long-living infrastructure that your application depends on. But on the other hand, that can lead to complex deployment orchestration or overcomplicated mono repo setups just to be able to deploy your stacks in the correct order with the right dependencies. This post will show you how you can use [Serverless Compose]([https://www.serverless.com/framework/docs/guides/compose](https://www.serverless.com/framework/docs/guides/compose)) to easily separate your stateful infrastructure into a separate stack and deploy it without the hassle!

## ♫ Serverless Compose

[Serverless Compose](https://www.serverless.com/framework/docs/guides/compose) is a feature of the [Serverless Framework](https://www.serverless.com/framework/docs) that simplifies orchestration and configuration when you have multiple related CloudFormation stacks. Apart from providing a simple configuration format for orchestrating and defining the services and their respective dependencies, it also provides CLI tooling to interact with those services once deployed, for example to stream the logs of those services directly to your stdout at the same time.

## 🎹 Composing an Application

The first thing we're going to need is a `serverless-compose.yml` file in the root of our project. This file will contain the configuration that instructs Serverless Compose what services (CloudFormation stacks) our application will consist of and how their deployments should be orchestrated. In an empty directory, create a file called `serverless-compose.yml` and list two services in it, one called **infrastructure** and one called **application**.

```yaml
services:
  infrastructure:
    path: infrastructure

  application:
    path: application
```

The **infrastructure** service will contain our stateful infrastructure, which in this case will be a DynamoDB table, while the **application** service will contain stateless resources, in this case, a Lambda function.

Let's start by implementing the **infrastructure service** by creating a subdirectory called **infrastructure**. Inside that directory, add a `serverless.yml` file and add the configuration to set up a DynamoDB table: 

```yaml
service: infrastructure

frameworkVersion: '3'

provider:
  name: aws

resources:
  Resources:
    DynamoTable:
      Type: AWS::DynamoDB::Table
      Properties:
        AttributeDefinitions:
          - AttributeName: id
            AttributeType: S
        KeySchema:
          - AttributeName: id
            KeyType: HASH
        BillingMode: PAY_PER_REQUEST
        TableName: dunder-mifflin-clients
  Outputs:
    TableName:
      Value: !Ref DynamoTable
```

Note that we've added an `Outputs` field that contains the name of the DynamoDB table. We can use this output to easily pass parameters between our services without having to specify the same properties in multiple places or storing them in a parameter store. To inject this property as a parameter in the **application** service, add a **parameters** field to the **service** definition in the root `serverless-compose.yml` file, referring to the output of the **infrastructure** stack

```yaml
services:
  infrastructure:
    path: infrastructure

  application:
    path: application
    params:
      tableName: ${infrastructure.TableName}
```

Next, it's time to implement the **application** service. Again, in the root of the project, create a subdirectory called **application** and add a `serverless.yml` file:

```yaml
service: application

frameworkVersion: '3'

provider:
  name: aws
  runtime: nodejs14.x

functions:
  hello:
    handler: handler.hello
		environment:
	    TABLE_NAME: ${param:tableName}
```

This configuration defines a Lambda function called "hello" that takes a `TABLE_NAME` as an environment variable. That variable is filled by the **parameter** we injected with the value from our **infrastructure** service.

To complete the **application** service, add the Lambda function `handler.js`

```jsx
module.exports.hello = async (event) => {
  return {
    statusCode: 200,
    body: JSON.stringify(
      {
        message: `I see you ${process.env.TABLE_NAME} 👀`,
        input: event,
      },
      null,
      2
    ),
  };
};
```

Finally, we don't want to risk our **application** service accidentally being deployed before our **infrastructure** service in case we do any changes to the DynamoDB table that in turn requires code changes to our **application** service. We can make sure we always deploy the **infrastructure** service first by specifying that the **application** service depends on the **infrastructure** service:

```yaml
services:
  infrastructure:
    path: infrastructure

  application:
    path: application
    params:
      tableName: ${infrastructure.TableName}
	dependsOn: infrastructure
```

We're now ready to deploy our application! In the root of the project, run `npx serverless deploy`  🚀


![2022-05-24_23-41-33.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1655540380826/qqcXrt-Z4u.png?auto=compress,format&format=webp)

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--- 

This post was [originally published](https://blog.elva-group.com/separate-stateful-infrastructure-with-serverless-compose) on the [Elva](https://elva-group.com/) blog. Elva is a serverless-first consulting company that can help you transform or begin your AWS journey for the future.