Tutorial: Deploying a Hello World application
In this guide, you download, build, and deploy a sample Hello World application using AWS SAM. You then test the application in the AWS Cloud, and optionally test it locally on your development host.
This application implements a simple API backend. It consists of an API Gateway endpoint
and a
Lambda function. When you send a GET request to the API Gateway endpoint, the Lambda
function is
invoked. This function returns a hello world message.
The following diagram shows the components of this application:
The following is a preview of commands that you run to create your Hello World application. For more details about each of these commands, see the sections later in this page
#Step 1 - Download a sample applicationsam init#Step 2 - Build your applicationcd sam-appsam build#Step 3 - Deploy your applicationsam deploy --guided
Prerequisites
This guide assumes that you've completed the steps in the Installing the AWS SAM CLI for your OS. It assumes that you've done the following:
-
Created an AWS account.
-
Configured IAM permissions.
-
Installed Docker. Note: Docker is only a prerequisite for testing your application locally.
-
Installed Homebrew. Note: Homebrew is only a prerequisite for Linux and macOS.
-
Installed the AWS SAM CLI. Note: Make sure you have version 1.0.0 or later. You can check which version you have by executing the command
sam --version.
Step 1: Download a sample AWS SAM application
Command to run:
sam init
Follow the on-screen prompts. For this tutorial we recommend you choose AWS Quick Start Templates, the runtime of your choice, and the Hello World Example.
Example output:
-----------------------
Generating application:
-----------------------
Name: sam-app
Runtime: python3.7
Dependency Manager: pip
Application Template: hello-world
Output Directory: .
Next steps can be found in the README file at ./sam-app/README.md
What AWS SAM is doing:
This command creates a directory with the name you provided as the project name. The contents of the project directory are similar to the following (these contents are created when one of the Python runtimes and the Hello World Example are chosen):
sam-app/
├── README.md
├── events/
│ └── event.json
├── hello_world/
│ ├── __init__.py
│ ├── app.py #Contains your AWS Lambda handler logic.
│ └── requirements.txt #Contains any Python dependencies the application requires, used for sam build
├── template.yaml #Contains the AWS SAM template defining your application's AWS resources.
└── tests/
└── unit/
├── __init__.py
└── test_handler.py
There are three especially important files:
-
template.yaml: Contains the AWS SAM template that defines your application's AWS resources. -
hello_world/app.py: Contains your actual Lambda handler logic. -
hello_world/requirements.txt: Contains any Python dependencies that the application requires, and is used forsam build.
Step 2: Build your application
Command to run:
First change into the project directory (that is, the directory where the
template.yaml file for the sample application is located; by default is
sam-app), then run this command:
sam build
Example output:
Build Succeeded
Built Artifacts : .aws-sam/build
Built Template : .aws-sam/build/template.yaml
Commands you can use next
=========================
[*] Invoke Function: sam local invoke
[*] Deploy: sam deploy --guided
What AWS SAM is doing:
The AWS SAM CLI comes with abstractions for a number of Lambda runtimes to build your
dependencies, and copies the source code into staging folders so that everything is
ready to be packaged and deployed. 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.
You can see the following top-level tree under .aws-sam:
.aws_sam/
└── build/
├── HelloWorldFunction/
└── template.yaml
HelloWorldFunction is a directory that contains your app.py
file, as well as third-party dependencies that your application uses.
Step 3: Deploy your application to the AWS Cloud
Command to run:
sam deploy --guided
Follow the on-screen prompts. You can just respond with Enter to accept
the default options provided in the interactive experience.
For the prompt HelloWorldFunction may not have authorization defined, Is
this okay? [y/N] AWS SAM is informing you that the sample application
configures an API Gateway API without authorization. When you deploy the sample
application, AWS SAM creates a publicly available URL.
You can acknowledge this notification by answering "Y" to the prompt. For information configuring authorization, see Controlling access to API Gateway APIs.
Example output:
Deploying with following values
===============================
Stack name : sam-app
Region : us-east-1
Confirm changeset : False
Deployment s3 bucket : sam-bucket
Capabilities : ["CAPABILITY_IAM"]
Parameter overrides : {}
Initiating deployment
=====================
Waiting for changeset to be created..
CloudFormation stack changeset
---------------------------------------------------------------------------------------------------------------------------------------------------
Operation LogicalResourceId ResourceType
---------------------------------------------------------------------------------------------------------------------------------------------------
+ Add HelloWorldFunctionHelloWorldPermissionProd AWS::Lambda::Permission
+ Add ServerlessRestApiDeployment47fc2d5f9d AWS::ApiGateway::Deployment
+ Add ServerlessRestApiProdStage AWS::ApiGateway::Stage
+ Add ServerlessRestApi AWS::ApiGateway::RestApi
* Modify HelloWorldFunctionRole AWS::IAM::Role
* Modify HelloWorldFunction AWS::Lambda::Function
---------------------------------------------------------------------------------------------------------------------------------------------------
2019-11-21 14:33:24 - Waiting for stack create/update to complete
CloudFormation events from changeset
-------------------------------------------------------------------------------------------------------------------------------------------------
ResourceStatus ResourceType LogicalResourceId ResourceStatusReason
-------------------------------------------------------------------------------------------------------------------------------------------------
UPDATE_IN_PROGRESS AWS::IAM::Role HelloWorldFunctionRole -
UPDATE_COMPLETE AWS::IAM::Role HelloWorldFunctionRole -
UPDATE_IN_PROGRESS AWS::Lambda::Function HelloWorldFunction -
UPDATE_COMPLETE AWS::Lambda::Function HelloWorldFunction -
CREATE_IN_PROGRESS AWS::ApiGateway::RestApi ServerlessRestApi -
CREATE_COMPLETE AWS::ApiGateway::RestApi ServerlessRestApi -
CREATE_IN_PROGRESS AWS::ApiGateway::RestApi ServerlessRestApi Resource creation Initiated
CREATE_IN_PROGRESS AWS::ApiGateway::Deployment ServerlessRestApiDeployment47fc2d5 Resource creation Initiated
f9d
CREATE_IN_PROGRESS AWS::Lambda::Permission HelloWorldFunctionHelloWorldPermis Resource creation Initiated
sionProd
CREATE_IN_PROGRESS AWS::Lambda::Permission HelloWorldFunctionHelloWorldPermis -
sionProd
CREATE_IN_PROGRESS AWS::ApiGateway::Deployment ServerlessRestApiDeployment47fc2d5 -
f9d
CREATE_COMPLETE AWS::ApiGateway::Deployment ServerlessRestApiDeployment47fc2d5 -
f9d
CREATE_IN_PROGRESS AWS::ApiGateway::Stage ServerlessRestApiProdStage -
CREATE_IN_PROGRESS AWS::ApiGateway::Stage ServerlessRestApiProdStage Resource creation Initiated
CREATE_COMPLETE AWS::ApiGateway::Stage ServerlessRestApiProdStage -
CREATE_COMPLETE AWS::Lambda::Permission HelloWorldFunctionHelloWorldPermis -
sionProd
UPDATE_COMPLETE_CLEANUP_IN_PROGRES AWS::CloudFormation::Stack sam-app -
S
UPDATE_COMPLETE AWS::CloudFormation::Stack sam-app -
-------------------------------------------------------------------------------------------------------------------------------------------------
Stack sam-app outputs:
---------------------------------------------------------------------------------------------------------------------------------------------------
OutputKey-Description OutputValue
---------------------------------------------------------------------------------------------------------------------------------------------------
HelloWorldFunctionIamRole - Implicit IAM Role created for Hello World arn:aws:iam::123456789012:role/sam-app-
function HelloWorldFunctionRole-104VTJ0TST7M0
HelloWorldApi - API Gateway endpoint URL for Prod stage for Hello World https://0ks2zue0zh.execute-api.us-east-1.amazonaws.com/Prod/hello/
function
HelloWorldFunction - Hello World Lambda Function ARN arn:aws:lambda:us-east-1:123456789012:function:sam-app-
HelloWorldFunction-1TY92MJX0BXU5
---------------------------------------------------------------------------------------------------------------------------------------------------
Successfully created/updated stack - sam-app in us-east-1
What AWS SAM is doing:
This command deploys your application to the AWS cloud. It takes the deployment
artifacts you build with the sam build command, packages and uploads them
to an Amazon S3 bucket created by AWS SAM CLI, and deploys the application using AWS
CloudFormation. In the
output of the deploy command you can see the changes being made to your AWS CloudFormation
stack.
If your application created a HTTP endpoint, the Outputs generated by sam
deploy also show you the endpoint URL for your test application. You can use
curl to send a request to your application using that endpoint URL. For
example:
curlhttps://<restapiid>.execute-api.us-east-1.amazonaws.com/Prod/hello/
You should see output like the following after successfully deploying your application:
{"message": "hello world"}
If you see {"message": "hello world"} after executing the
curl command, it means that you've successfully deployed your
serverless application to AWS, and are calling your live Lambda function. Otherwise,
see
the Troubleshooting section
later in this tutorial.
Step 4: Testing your application locally (optional)
When you're developing your application, you might also find it useful to test
locally. The AWS SAM CLI provides the sam local command to run your
application using Docker containers that simulate the execution environment of Lambda.
There are two options to do this:
-
Host your API locally
-
Invoke your Lambda function directly
This step describes both options.
Host your API locally
Command to run:
sam local start-api
Example output:
2019-07-12 15:27:58 Mounting HelloWorldFunction at http://127.0.0.1:3000/hello [GET]
2019-07-12 15:27:58 You can now browse to the above endpoints to invoke your functions. You do not need to restart/reload SAM CLI while working on your functions, changes will be reflected instantly/automatically. You only need to restart SAM CLI if you update your AWS SAM template
2019-07-12 15:27:58 * Running on http://127.0.0.1:3000/ (Press CTRL+C to quit)
Fetching lambci/lambda:python3.7 Docker container image......................................................................................................................................................................................
2019-07-12 15:28:56 Mounting /<working-development-path>/sam-app/.aws-sam/build/HelloWorldFunction as /var/task:ro,delegated inside runtime container
START RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72 Version: $LATEST
END RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72
REPORT RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72 Duration: 4.42 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 22 MB
2019-07-12 15:28:58 No Content-Type given. Defaulting to 'application/json'.
2019-07-12 15:28:58 127.0.0.1 - - [12/Jul/2019 15:28:58] "GET /hello HTTP/1.1" 200 -
It might take a while for the Docker image to load. After it's loaded, you can use
curl to send a request to your application that's running on your
local host:
curl http://127.0.0.1:3000/hello
Example output:
2019-07-12 15:29:57 Invoking app.lambda_handler (python3.7) 2019-07-12 15:29:57 Found credentials in shared credentials file: ~/.aws/credentials Fetching lambci/lambda:python3.7 Docker container image...... 2019-07-12 15:29:58 Mounting /<working-development-path>/sam-app/.aws-sam/build/HelloWorldFunction as /var/task:ro,delegated inside runtime container START RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72 Version: $LATEST END RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72 REPORT RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72 Duration: 7.92 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 22 MB {"statusCode":200,"body":"{\"message\": \"hello world\"}"}
What AWS SAM is doing:
The start-api command starts up a local endpoint that replicates your
REST API endpoint. It downloads an execution container that you can run your
function locally in. The end result is the same output that you saw when you called
your function in the AWS Cloud.
Making one-off invocations
Command to run:
sam local invoke "HelloWorldFunction" -e events/event.json
Example output:
2019-07-01 14:08:42 Found credentials in shared credentials file: ~/.aws/credentials 2019-07-01 14:08:42 Invoking app.lambda_handler (python3.7) Fetching lambci/lambda:python3.7 Docker container image............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... 2019-07-01 14:09:39 Mounting /<working-development-path>/sam-app/.aws-sam/build/HelloWorldFunction as /var/task:ro,delegated inside runtime container START RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72 Version: $LATEST END RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72 REPORT RequestId: 52fdfc07-2182-154f-163f-5f0f9a621d72 Duration: 3.51 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 22 MB {"statusCode":200,"body":"{\"message\": \"hello world\"}"}
What AWS SAM is doing:
The invoke command directly invokes your Lambda functions, and can
pass input event payloads that you provide. With this command, you pass the event
payload in the file event.json that's provided by the sample
application.
Your initialized application came with a default aws-proxy event for
API Gateway. A number of values are prepopulated for you. In this case, the
HelloWorldFunction doesn't care about the particular values, so a
stubbed request is OK. You can specify a number of values to be substituted in to
the request to simulate what you would expect from an actual request. This following
is an example of generating your own input event and comparing the output with the
default event.json object:
sam local generate-event apigateway aws-proxy --body "" --path "hello" --method GET > api-event.json diff api-event.json event.json
Example output:
< "body": "",
---
> "body": "{\"message\": \"hello world\"}",
4,6c4,6
< "path": "/hello",
< "httpMethod": "GET",
< "isBase64Encoded": true,
---
> "path": "/path/to/resource",
> "httpMethod": "POST",
> "isBase64Encoded": false,
11c11
< "proxy": "/hello"
---
> "proxy": "/path/to/resource"
56c56
< "path": "/prod/hello",
---
> "path": "/prod/path/to/resource",
58c58
< "httpMethod": "GET",
---
> "httpMethod": "POST",
Troubleshooting
SAM CLI error: "Security Constraints Not Satisfied"
When executing sam deploy --guided, you are prompted with the question
HelloWorldFunction may not have authorization defined, Is this okay? [y/N].
If you respond to this prompt with "N" (the default response), you see the following
error:
Error: Security Constraints Not Satisfied
The prompt is informing you that the application you're about to deploy may have an API Gateway API configured without authorization. By responding "N" to this prompt (the default), you are saying this is not OK.
To fix this, you have the following options:
-
Configure your application with authorization. For information configuring authorization, see Controlling access to API Gateway APIs.
-
Respond to this question with "Y" to indicate that you are OK with deploying an application that has an API Gateway API configured without authorization.
SAM CLI error: "no such option: --app-template"
When executing sam init, you see the following error:
Error: no such option: --app-template
This means that you are using an older version of the AWS SAM CLI that does not
support the --app-template parameter. To fix this, you can either
update your version of AWS SAM CLI to 0.33.0 or later, or omit the
--app-template parameter from the sam init
command.
SAM CLI error: "no such option: --guided"
When executing sam deploy, you see the following error:
Error: no such option: --guided
This means that you are using an older version of the AWS SAM CLI that does not
support the --guided parameter. To fix this, you can either update your
version of AWS SAM CLI to 0.33.0 or later, or omit the --guided parameter
from the sam deploy command.
SAM CLI error: "Failed to create managed resources: Unable to locate credentials"
When executing sam deploy, you see the following error:
Error: Failed to create managed resources: Unable to locate credentials
This means that you have not set up AWS credentials to enable the AWS SAM CLI to make AWS service calls. To fix this, you must set up AWS credentials. For more information, see Setting up AWS credentials.
SAM CLI error: "Running AWS SAM projects locally requires Docker. Have you got it installed?"
When executing sam local start-api, you see the following
error:
Error: Running AWS SAM projects locally requires Docker. Have you got it installed?
This means that you do not have Docker properly installed. Docker is required to test your application locally. To fix this, follow the instructions for installing Docker for your development host.
For instructions on installing Docker on your development host, go to Installing the AWS SAM CLI, choose the appropriate platform, and follow the instructions in the section titled Install Docker.
Curl Error: "Missing Authentication Token"
When trying to invoke the API Gateway endpoint, you see the following error:
{"message":"Missing Authentication Token"}
This means that you've attempted to send a request to the correct domain, but the
URI isn't recognizable. To fix this, verify the full URL, and update the
curl command with the correct URL.
Curl Error: "curl: (6) Could not resolve: ..."
When trying to invoke the API Gateway endpoint, you see the following error:
curl: (6) Could not resolve: endpointdomain (Domain name not found)
This means that you've attempted to send a request to an invalid domain. This can
happen if your serverless application failed to deploy successfully, or if you have
a typo in your curl command. Verify that the application was deployed
successfully by using the AWS CloudFormation console or AWS CLI, and that your curl
command is correct.
Clean up
If you no longer need the AWS resources you created by running this tutorial, you can remove them by deleting the AWS CloudFormation stack that you deployed.
To delete the AWS CloudFormation stack created with this tutorial using the AWS Management Console, follow these steps:
-
Sign in to the AWS Management Console and open the AWS CloudFormation console at https://console.aws.amazon.com/cloudformation
. -
In the left navigation pane, choose Stacks.
-
In the list of stacks, choose sam-app (or the name of stack you created).
-
Choose Delete.
When done, the status of the of the stack will change to DELETE_COMPLETE.
Alternatively, you can delete the AWS CloudFormation stack by executing the following AWS CLI command:
aws cloudformation delete-stack --stack-namesam-app--regionregion
Verify deleted stack
For both methods of deleting the AWS CloudFormation stack, you can verify it was deleted
by
going to the https://console.aws.amazon.com/cloudformation
Conclusion
In this tutorial, you've done the following:
-
Created, built, and deployed a serverless application to AWS with AWS SAM.
-
Tested your application locally by using the AWS SAM CLI and Docker.
-
Deleted the AWS resources that you no longer need.
Next steps
You're now ready to start building your own applications using the AWS SAM CLI.
To help you get started, you can download any of the example applications from the
AWS SAM GitHub repository. To access this repository, see AWS SAM example
applications
