A simpler deployment experience with AWS SAM CLI

The AWS Serverless Application Model (SAM) CLI provides developers with a local tool for managing serverless applications on AWS. The command line tool allows developers to initialize and configure applications, debug locally using IDEs like Visual Studio Code or JetBrains WebStorm, and deploy to the AWS Cloud.

On November 25, we announced improvements to the deployment process using the SAM CLI. These improvements allow users to deploy serverless applications with less manual setup, fewer repeated steps, and shorter CLI commands.

To install the latest version of the AWS SAM CLI, please refer to the installation section of the AWS SAM page.

What’s new?

Amazon S3 bucket management

Previously, developers had to manually create and manage an Amazon S3 bucket to host deployment artifacts for each desired Region. With this latest release, the SAM CLI automatically creates a Region-specific bucket via AWS CloudFormation, based on your local AWS credentials. If you deploy an application to a Region where no bucket exists, a new managed bucket is created in the new Region.

Minimized deployment commands

Before this update, a minimal deployment process would look like this:

sam package --s3-bucket my-regional-bucket --output-template-file out.yaml
sam deploy --template-file out.yaml --capabilities CAPABILITY_IAM --stack-name MyStackName

This series of commands was required at every deployment. With this latest update to SAM CLI, the package and deployment commands have been combined. The syntax is now:

sam deploy

The guided deployment

How does SAM CLI know where to deploy and what to name the application? The answer to this is found in the “guided deployment.” This is an interactive version of the deployment process that collects and saves information needed to deploy the application.

If sam deploy is running and cannot find the required information for deployment, the process errors out, recommending that the guided deployment process be run. To use the guided process:

sam deploy -g or --guided

Once the information is collected, it is saved in the application as the samconfig.toml file. Subsequent calls to sam deploy use the existing data to deploy. If you update a setting between deployments, run the sam deploy -g command again to update the stored values.

Frequently asked questions

How many buckets are created?

When you run the sam deploy -g command with provided values, SAM checks the account for an existing SAM deployment bucket in that Region. This Regional bucket is created via CloudFormation by SAM as an artifact repository for all applications for the current account in the current Region. For a root level account, there is only a single bucket per Region that contains deployed SAM serverless applications.

What if the Region is changed for the application?

If you change the Region in samconfig.toml before running sam deploy, the process errors out. The selected deployment Region does not match the artifacts bucket Region stored in the samconfig.toml file. The error also occurs if you use the –region flag, and a Region is different to the Region in the samconfig.toml file. To change the Region for a deployment, use the sam deploy -g option to update the Region. SAM verifies that a bucket for the new Region exists, or creates one automatically.

What if the samconfig.toml file is deleted?

If the samconfig.toml file is deleted, SAM treats the application as new. We recommend that you use the -g flag to reconfigure the application.

What about backwards compatibility?

If you are using SAM for a non-interactive deployment, it is possible to pass all required information as parameters. For example, for a continuous integration continuous delivery (CICD) pipeline:

This same deployment is achieved using the older process with the following commands:

sam package --s3-bucket aws-sam-cli-managed-default-samclisourcebucket-xic3fipuh9n9 --output-template-file out.yaml
sam deploy --template-file out.yaml --capabilities CAPABILITY_IAM --stack-name sam-app --region us-west-2

The package command still exists in the latest version of SAM CLI for backwards compatibility with existing CICD processes.

Updated user experience

Along a streamlined process for deploying applications, the new version of SAM CLI brings an improved user interface. This provides developers with more feedback and validation choices. First, during the deployment process, all deployment parameters are displayed:

Once the changeset is created, the developer is presented with all the proposed changes.

Developers also have the option to confirm the changes, or cancel the deployment. This option is a setting in the samconfig.toml file that can be turned on or off as needed.

As the changeset is applied, the console displays the changes being made in the AWS Cloud.

Finally, the resulting output is displayed.

Conclusion

By streamlining the deployment process, removing the need to manage an S3 bucket, and providing clear deployment feedback and data, the latest version SAM CLI makes serverless development easier for developers.

Happy coding and deploying!