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Alejandro Lazaro for AWS Community Builders

Posted on • Updated on • Originally published at playingaws.com

How to create serverless applications with AWS SAM (Serverless Application Model)

#sam #serverless #iac #aws

This is the second article of a serie about AWS SAM. The next will be one related with the deployment.

To keep it simple, we will create a SAM application from a quick start template using the standalone function. However you could try a different template, the steps to follow should be the same.

The code example is available in GitHub repository here. If you want to see the step by step you can check the commit history, where you can find the evolution of the application through the steps explained in the following lines.

These are all the steps that I want to show you in this article:

  • Step 1: Create a SAM application
  • Step 2 (Optional): Test your application locally
  • Step 3 (Optional): Unit test
  • Step 4: Build your application
  • Step 5: Deploy manually your application with the CLI
  • Step 6 (Optional): AWS SAM Accelerate (Preview) - Sync

Step 1: Create a sample SAM application

The first step is to create our application through a quick start template: Standalone function.

To create a new application from a template we run the sam init command.

> sam init
Which template source would you like to use?
1 - AWS Quick Start Templates
2 - Custom Template Location
Choice: > 1

Choose an AWS Quick Start application template
  1 - Hello World Example
  2 - Data processing
  3 - Hello World Example with Powertools for AWS Lambda
  4 - Multi-step workflow
  5 - Scheduled task
  6 - Standalone function
  7 - Serverless API
  8 - Infrastructure event management
  9 - Lambda Response Streaming
  10 - Serverless Connector Hello World Example
  11 - Multi-step workflow with Connectors
  12 - GraphQLApi Hello World Example
  13 - Full Stack
  14 - Lambda EFS example
  15 - Hello World Example With Powertools for AWS Lambda
  16 - DynamoDB Example
  17 - Machine Learning
Template: > 6

Which runtime would you like to use?
  1 - dotnet6
  2 - nodejs20.x
  3 - nodejs18.x
  4 - nodejs16.x
Runtime: > 2

Based on your selections, the only Package type available is Zip.
We will proceed to selecting the Package type as Zip.

Based on your selections, the only dependency manager available is npm.
We will proceed copying the template using npm.

Would you like to enable X-Ray tracing on the function(s) in your application?  [y/N]: > N

Would you like to enable monitoring using CloudWatch Application Insights?
For more info, please view https://docs.aws.amazon.com/AmazonCloudWatch/latest/monitoring/cloudwatch-application-insights.html [y/N]: > N

Would you like to set Structured Logging in JSON format on your Lambda functions?  [y/N]:

Project name [sam-app]: > sam-app

    -----------------------
    Generating application:
    -----------------------
    Name: sam-app
    Runtime: nodejs20.x
    Architectures: x86_64
    Dependency Manager: npm
    Application Template: quick-start-from-scratch
    Output Directory: .
    Configuration file: sam-app/samconfig.toml

    Next steps can be found in the README file at sam-app/README.md


Commands you can use next
=========================
[*] Create pipeline: cd sam-app && sam pipeline init --bootstrap
[*] Validate SAM template: cd sam-app && sam validate
[*] Test Function in the Cl
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At the end of the command line messages appears Commands you can use next, where other SAM CLI commands are suggested as the next steps to execute.

This is the basic application that has been created (only with one lambda function for easy understanding):

Code basic

Note that we have 4 of the 5 files that we reviewed before:

  • src/handlers/hello-from-lambda.js
  • _test_/unit/handlers/hello-from-lambda.test.js
  • template.yaml
  • package.json

We don't have the folder events because we only create one simple Lambda Function with no event integrations

Step 2 (Optional): Test your application locally

The AWS SAM CLI provides the sam local command to run your application using Docker containers that simulate the execution environment of Lambda.

Invoke your Lambda function running sam local invoke:

> sam local invoke
Invoking src/handlers/hello-from-lambda.helloFromLambdaHandler (nodejs20.x)
Local image was not found.
Removing rapid images for repo public.ecr.aws/sam/emulation-nodejs20.x
Building image.............................................................................................................................................................................................................................................................................
Using local image: public.ecr.aws/lambda/nodejs:20-rapid-x86_64.

Mounting /Users/alazaroc/Documents/MyProjects/github/aws/sam/sam-app as /var/task:ro,delegated, inside
runtime container
START RequestId: ba22ff8c-02f8-42a7-980d-0f0248ee63bf Version: $LATEST
2024-01-22T22:11:35.245Z    ae4b9347-e347-4ec0-a7a1-f34a3533ec8b    INFO    Hello from Lambda!
END RequestId: ae4b9347-e347-4ec0-a7a1-f34a3533ec8b
REPORT RequestId: ae4b9347-e347-4ec0-a7a1-f34a3533ec8b  Init Duration: 0.06 ms  Duration: 181.07 ms Billed Duration: 182 ms Memory Size: 128 MB Max Memory Used: 128 MB
"Hello from Lambda!"
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We received the response "Hello from Lambda!" and more useful information (Duration, Billed Duration, Memory Size, or Max Memory Used).

If you have more than one Lambda Function, you must add the name which appears in the template.yaml file.

sam local invoke "helloFromLambdaFunction"
Invoking src/handlers/hello-from-lambda.helloFromLambdaHandler (nodejs20.x)
Local image is up-to-date
Using local image: public.ecr.aws/lambda/nodejs:20-rapid-x86_64.

Mounting /Users/alazaroc/Documents/MyProjects/github/aws/sam/sam-app as /var/task:ro,delegated, inside
runtime container
START RequestId: 323bbea4-2d41-407d-97b6-8605cbe454c3 Version: $LATEST
2024-01-22T22:20:25.541Z    9fadbf3c-0c9f-4728-b1a7-4ab96e715172    INFO    Hello from Lambda!
END RequestId: 9fadbf3c-0c9f-4728-b1a7-4ab96e715172
REPORT RequestId: 9fadbf3c-0c9f-4728-b1a7-4ab96e715172  Init Duration: 0.05 ms  Duration: 142.91 ms Billed Duration: 143 ms Memory Size: 128 MB Max Memory Used: 128 MB
"Hello from Lambda!"
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You also can test an API locally if your SAM project includes it.

You should run sam local start-api command, which starts up a local endpoint that replicates your REST API endpoint.

Step 3 (Optional): Unit test

Tests are defined in the _tests_ folder in this project. Use npm to install the Jest test framework and run unit tests.

npm install
...
npm run test
> replaced-by-user-input@0.0.1 test
> node --experimental-vm-modules node_modules/jest/bin/jest.js

  console.info
    Hello from Lambda!

      at helloFromLambdaHandler (src/handlers/hello-from-lambda.mjs:9:13)

(node:31412) ExperimentalWarning: VM Modules is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
PASS  __tests__/unit/handlers/hello-from-lambda.test.mjs
  Test for hello-from-lambda
    ✓ Verifies successful response (30 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.553 s
Ran all test suites.
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Step 4: Build your application

The sam build command builds any dependencies that your application has, and copies your application source code to folders under .aws-sam/build to be zipped and uploaded to Lambda.

> sam build
Starting Build use cache
Manifest file is changed (new hash: 57574ed173cdc6a98b283bd7b00b44ca) or dependency folder
(.aws-sam/deps/ee51225c-b9b8-433f-ab8b-3821871f820a) is missing for (helloFromLambdaFunction), downloading
dependencies and copying/building source
Building codeuri: /Users/alazaroc/Documents/MyProjects/github/aws/sam/sam-app runtime: nodejs20.x metadata:
{} architecture: x86_64 functions: helloFromLambdaFunction
Running NodejsNpmBuilder:NpmPack
Running NodejsNpmBuilder:CopyNpmrcAndLockfile
Running NodejsNpmBuilder:CopySource
Running NodejsNpmBuilder:NpmInstall
Running NodejsNpmBuilder:CleanUp
Running NodejsNpmBuilder:CopyDependencies
Running NodejsNpmBuilder:CleanUpNpmrc
Running NodejsNpmBuilder:LockfileCleanUp
Running NodejsNpmBuilder:LockfileCleanUp

Build Succeeded

Built Artifacts  : .aws-sam/build
Built Template   : .aws-sam/build/template.yaml

Commands you can use next
=========================
[*] Validate SAM template: sam validate
[*] Invoke Function: sam local invoke
[*] Test Function in the Cloud: sam sync --stack-name {{stack-name}} --watch
[*] Deploy: sam deploy --guided
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These are the new files of our SAM project:

build files

Step 5: Deploy manually your application with the CLI

Now we want to deploy our application and We will do it manually using the CLI, although in this other article. I will explain how to do it with a pipeline (automatically).

Remember that AWS SAM uses AWS CloudFormation as the underlying deployment mechanism.

As we don't have a configuration file containing all the values, we are going to create one. We run the sam deploy -- guided command which will search as a first step if a samconfig.toml file exists and if not the AWS SAM CLI will ask us about the necessary information to deploy our application.

The sam deploy command will package and upload the application artifacts to the S3 bucket, and deploys the application using AWS CloudFormation

> sam deploy --guided
Configuring SAM deploy
======================

  Looking for config file [samconfig.toml] :  Found
  Reading default arguments  :  Success

  Setting default arguments for 'sam deploy'
  =========================================
  Stack Name [sam-app]:
  AWS Region [eu-west-1]:
  #Shows you resources changes to be deployed and require a 'Y' to initiate deploy
  Confirm changes before deploy [Y/n]:
  #SAM needs permission to be able to create roles to connect to the resources in your template
  Allow SAM CLI IAM role creation [Y/n]:
  #Preserves the state of previously provisioned resources when an operation fails
  Disable rollback [y/N]:
  Save arguments to configuration file [Y/n]:
  SAM configuration file [samconfig.toml]:
  SAM configuration environment [default]:

  Looking for resources needed for deployment:

  Managed S3 bucket: aws-sam-cli-managed-default-samclisourcebucket-k2z3x0eqvuxq
  A different default S3 bucket can be set in samconfig.toml and auto resolution of buckets turned off by setting resolve_s3=False

        Parameter "stack_name=sam-app" in [default.deploy.parameters] is defined as a global parameter
[default.global.parameters].
        This parameter will be only saved under [default.global.parameters] in
/Users/alazaroc/Documents/MyProjects/github/aws/sam/sam-app/samconfig.toml.

  Saved arguments to config file
  Running 'sam deploy' for future deployments will use the parameters saved above.
  The above parameters can be changed by modifying samconfig.toml
  Learn more about samconfig.toml syntax at
  https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-config.html

  Uploading to sam-app/c20f3d4923fb213486783dd25f269a52  38478 / 38478  (100.00%)

  Deploying with following values
  ===============================
  Stack name                   : sam-app
  Region                       : eu-west-1
  Confirm changeset            : True
  Disable rollback             : False
  Deployment s3 bucket         : aws-sam-cli-managed-default-samclisourcebucket-k2z3x0eqvuxq
  Capabilities                 : ["CAPABILITY_IAM"]
  Parameter overrides          : {}
  Signing Profiles             : {}

Initiating deployment
=====================

  Uploading to sam-app/3752a1ab023524618cd64cc55081484c.template  734 / 734  (100.00%)


Waiting for changeset to be created..

CloudFormation stack changeset
-------------------------------------------------------------------------------------------------------------
Operation                   LogicalResourceId           ResourceType                Replacement
-------------------------------------------------------------------------------------------------------------
+ Add                       helloFromLambdaFunctionRo   AWS::IAM::Role              N/A
                            le
+ Add                       helloFromLambdaFunction     AWS::Lambda::Function       N/A
-------------------------------------------------------------------------------------------------------------


Changeset created successfully. arn:aws:cloudformation:eu-west-1:000000000000:changeSet/samcli-deploy1705962828/ee61a1a2-9083-4029-9ee1-126661b04541


Previewing CloudFormation changeset before deployment
======================================================
Deploy this changeset? [y/N]: y

2024-01-22 23:34:17 - Waiting for stack create/update to complete

CloudFormation events from stack operations (refresh every 5.0 seconds)
-------------------------------------------------------------------------------------------------------------
ResourceStatus              ResourceType                LogicalResourceId           ResourceStatusReason
-------------------------------------------------------------------------------------------------------------
CREATE_IN_PROGRESS          AWS::CloudFormation::Stac   sam-app                     User Initiated
                            k
CREATE_IN_PROGRESS          AWS::IAM::Role              helloFromLambdaFunctionRo   -
                                                        le
CREATE_IN_PROGRESS          AWS::IAM::Role              helloFromLambdaFunctionRo   Resource creation
                                                        le                          Initiated
CREATE_COMPLETE             AWS::IAM::Role              helloFromLambdaFunctionRo   -
                                                        le
CREATE_IN_PROGRESS          AWS::Lambda::Function       helloFromLambdaFunction     -
CREATE_IN_PROGRESS          AWS::Lambda::Function       helloFromLambdaFunction     Resource creation
                                                                                    Initiated
CREATE_COMPLETE             AWS::Lambda::Function       helloFromLambdaFunction     -
CREATE_COMPLETE             AWS::CloudFormation::Stac   sam-app                     -
                            k
-------------------------------------------------------------------------------------------------------------

Successfully created/updated stack - sam-app in eu-west-1
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Remember that the executed command will create the samconfig.toml file in our project to save the deployment configuration and be able to repeat it without configuration.

deploy guided

From now on, to deploy our SAM project we just need to run the sam deploy command, so we run it but if we have no changes, the deployment will fail:

> sam deploy
Managed S3 bucket: aws-sam-cli-managed-default-samclisourcebucket-k2z3x0eqvuxq
    A different default S3 bucket can be set in samconfig.toml
    Or by specifying --s3-bucket explicitly.
File with same data already exists at sam-app/c20f3d4923fb213486783dd25f269a52, skipping upload

  Deploying with following values
  ===============================
  Stack name                   : sam-app
  Region                       : eu-west-1
  Confirm changeset            : True
  Disable rollback             : False
  Deployment s3 bucket         : aws-sam-cli-managed-default-samclisourcebucket-k2z3x0eqvuxq
  Capabilities                 : ["CAPABILITY_IAM"]
  Parameter overrides          : {}
  Signing Profiles             : {}

Initiating deployment
=====================

File with same data already exists at sam-app/3752a1ab023524618cd64cc55081484c.template, skipping upload


Waiting for changeset to be created..

Error: No changes to deploy. Stack sam-app is up to date
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Step 6 (Optional): AWS SAM Sync

We already have deployed our application in the cloud and you may want to synchronize the changes, i.e. deploy the changes in real-time when we save the changes (without running the deploy command).

The sam sync command syncs your local application changes to the AWS Cloud. Use sync to build, package, and deploy changes to your development environment as you iterate on your application. As a best practice, run sam sync after you finish iterating on your application to sync changes to your AWS CloudFormation stack.

Be careful if you use this functionality.

First it is in preview and also as you will see in the next lines in the console: "The SAM CLI will use the AWS Lambda, Amazon API Gateway, and AWS StepFunctions APIs to upload your code without performing a CloudFormation deployment. This will cause drift in your CloudFormation stack."

The sync command should only be used against a development stack.

> sam sync --stack-name sam-app --watch
The SAM CLI will use the AWS Lambda, Amazon API Gateway, and AWS StepFunctions APIs to upload your code without
performing a CloudFormation deployment. This will cause drift in your CloudFormation stack.
**The sync command should only be used against a development stack**.

Confirm that you are synchronizing a development stack.

Enter Y to proceed with the command, or enter N to cancel:
[Y/n]:
Queued infra sync. Waiting for in progress code syncs to complete...
Starting infra sync.
Manifest is not changed for (helloFromLambdaFunction), running incremental build
Building codeuri: /Users/alazaroc/Documents/MyProjects/github/aws/sam/sam-app runtime: nodejs20.x
metadata: {} architecture: x86_64 functions: helloFromLambdaFunction
Running NodejsNpmBuilder:NpmPack
Running NodejsNpmBuilder:CopyNpmrcAndLockfile
Running NodejsNpmBuilder:CopySource
Running NodejsNpmBuilder:CleanUpNpmrc
Running NodejsNpmBuilder:LockfileCleanUp
Running NodejsNpmBuilder:LockfileCleanUp

Build Succeeded

Successfully packaged artifacts and wrote output template to file /var/folders/wq/bz6xngtx5h3f5gf8py3kf28c0000gn/T/tmppcg60qga.
Execute the following command to deploy the packaged template
sam deploy --template-file /var/folders/wq/bz6xngtx5h3f5gf8py3kf28c0000gn/T/tmppcg60qga --stack-name <YOUR STACK NAME>


  Deploying with following values
  ===============================
  Stack name                   : sam-app
  Region                       : eu-west-1
  Disable rollback             : False
  Deployment s3 bucket         : aws-sam-cli-managed-default-samclisourcebucket-k2z3x0eqvuxq
  Capabilities                 : ["CAPABILITY_NAMED_IAM", "CAPABILITY_AUTO_EXPAND"]
  Parameter overrides          : {}
  Signing Profiles             : null

Initiating deployment
=====================


2024-01-22 23:43:31 - Waiting for stack create/update to complete

CloudFormation events from stack operations (refresh every 0.5 seconds)
---------------------------------------------------------------------------------------------------------
ResourceStatus             ResourceType               LogicalResourceId          ResourceStatusReason
---------------------------------------------------------------------------------------------------------
UPDATE_IN_PROGRESS         AWS::CloudFormation::Sta   sam-app                    User Initiated
                          ck
UPDATE_IN_PROGRESS         AWS::CloudFormation::Sta   sam-app                    Transformation succeeded
                          ck
CREATE_IN_PROGRESS         AWS::CloudFormation::Sta   AwsSamAutoDependencyLaye   -
                          ck                         rNestedStack
CREATE_IN_PROGRESS         AWS::CloudFormation::Sta   AwsSamAutoDependencyLaye   Resource creation
                          ck                         rNestedStack               Initiated
CREATE_COMPLETE            AWS::CloudFormation::Sta   AwsSamAutoDependencyLaye   -
                          ck                         rNestedStack
UPDATE_IN_PROGRESS         AWS::Lambda::Function      helloFromLambdaFunction    -
UPDATE_COMPLETE            AWS::Lambda::Function      helloFromLambdaFunction    -
UPDATE_COMPLETE_CLEANUP_   AWS::CloudFormation::Sta   sam-app                    -
IN_PROGRESS                ck
UPDATE_COMPLETE            AWS::CloudFormation::Sta   sam-app                    -
                          ck
---------------------------------------------------------------------------------------------------------

Stack update succeeded. Sync infra completed.

Infra sync completed.
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The console still listens for changes and if we change our lambda code and save it:

sync lambda

The console will be updated automatically as follow:

Syncing Lambda Function helloFromLambdaFunction...
Manifest is not changed for (helloFromLambdaFunction), running incremental build
Building codeuri: /Users/alazaroc/Documents/MyProjects/github/aws/sam/sam-app runtime: nodejs20.x
metadata: {} architecture: x86_64 functions: helloFromLambdaFunction
 Running NodejsNpmBuilder:NpmPack
 Running NodejsNpmBuilder:CopyNpmrcAndLockfile
 Running NodejsNpmBuilder:CopySource
 Running NodejsNpmBuilder:CleanUpNpmrc
 Running NodejsNpmBuilder:LockfileCleanUp
 Running NodejsNpmBuilder:LockfileCleanUp
Finished syncing Lambda Function helloFromLambdaFunction.
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When you stop it (control + C) in the console it will appear:

^CShutting down sync watch...
Sync watch stopped.
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When you executed the sync command, a nested stack associated with your main stack (sam-app) was created:

nested stack

And when the console stops being synchronized, this nested stack is NOT deleted.

How to remove the nested stack created with the sync command?

You have to run the sam deploy command again and it will be removed:

> sam deploy
Managed S3 bucket: aws-sam-cli-managed-default-samclisourcebucket-k2z3x0eqvuxq
      A different default S3 bucket can be set in samconfig.toml
      Or by specifying --s3-bucket explicitly.
  File with same data already exists at sam-app/c20f3d4923fb213486783dd25f269a52, skipping upload

    Deploying with following values
    ===============================
    Stack name                   : sam-app
    Region                       : eu-west-1
    Confirm changeset            : True
    Disable rollback             : False
    Deployment s3 bucket         : aws-sam-cli-managed-default-samclisourcebucket-k2z3x0eqvuxq
    Capabilities                 : ["CAPABILITY_IAM"]
    Parameter overrides          : {}
    Signing Profiles             : {}

  Initiating deployment
  =====================

  File with same data already exists at sam-app/3752a1ab023524618cd64cc55081484c.template, skipping upload


  Waiting for changeset to be created..

  CloudFormation stack changeset
  ---------------------------------------------------------------------------------------------------------
  Operation                  LogicalResourceId          ResourceType               Replacement
  ---------------------------------------------------------------------------------------------------------
  * Modify                   helloFromLambdaFunction    AWS::Lambda::Function      False
  - Delete                   AwsSamAutoDependencyLaye   AWS::CloudFormation::Sta   N/A
                            rNestedStack               ck
  ---------------------------------------------------------------------------------------------------------

  Changeset created successfully. arn:aws:cloudformation:eu-west-1:000000000000:changeSet/samcli-deploy1705963790/6b5464b9-0b8e-44c2-93c0-8e0f509c9110


  Previewing CloudFormation changeset before deployment
  ======================================================
  Deploy this changeset? [y/N]: y

  2024-01-22 23:50:02 - Waiting for stack create/update to complete

  CloudFormation events from stack operations (refresh every 5.0 seconds)
  ---------------------------------------------------------------------------------------------------------
  ResourceStatus             ResourceType               LogicalResourceId          ResourceStatusReason
  ---------------------------------------------------------------------------------------------------------
  UPDATE_IN_PROGRESS         AWS::CloudFormation::Sta   sam-app                    User Initiated
                            ck
  UPDATE_IN_PROGRESS         AWS::Lambda::Function      helloFromLambdaFunction    -
  UPDATE_COMPLETE            AWS::Lambda::Function      helloFromLambdaFunction    -
  UPDATE_COMPLETE_CLEANUP_   AWS::CloudFormation::Sta   sam-app                    -
  IN_PROGRESS                ck
  DELETE_IN_PROGRESS         AWS::CloudFormation::Sta   AwsSamAutoDependencyLaye   -
                            ck                         rNestedStack
  DELETE_COMPLETE            AWS::CloudFormation::Sta   AwsSamAutoDependencyLaye   -
                            ck                         rNestedStack
  UPDATE_COMPLETE            AWS::CloudFormation::Sta   sam-app                    -
                            ck
  ---------------------------------------------------------------------------------------------------------

  Successfully created/updated stack - sam-app in eu-west-1
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Step 7: Clean up

If you are followed this tutorial you will only have one stack in our AWS Account, so you can run the sam delete command (which deletes the main stack: sam-app).

> sam delete
Are you sure you want to delete the stack sam-app in the region eu-west-1 ? [y/N]: y
Are you sure you want to delete the folder sam-app in S3 which contains the artifacts? [y/N]: y
      - Deleting S3 object with key sam-app/c20f3d4923fb213486783dd25f269a52
      - Deleting S3 object with key sam-app/3752a1ab023524618cd64cc55081484c.template
- Deleting Cloudformation stack sam-app

Deleted successfully
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Next steps

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