Creating Serverless Application with API Gateway and Lambda
We will combine two resources to create a simple serverless web application.
The first is Lambda. Lambda is a FaaS service provided by AWS.
AWS Lambda is a serverless compute service that runs your code in response to events and automatically manages the underlying compute resources for you.
AWS Lambda Features
In this case, we will use Lambda as a computing resource for our web app.
The second is API Gateway, which is a fully managed service provided by AWS for building APIs.
Amazon API Gateway is a fully managed service that makes it easy for developers to publish, maintain, monitor, secure, and operate APIs at any scale.
Amazon API Gateway Features
In this case, an HTTP type API Gateway is used as an endpoint to access the web application.
For details on how to create a REST API type API Gateway, please refer to the following page.
Environment
Create an API Gateway and place Lambda in the backend.
In this simple configuration, when an HTTP request is received from a user, the API Gateway becomes the endpoint, calls a Lambda function instead, and returns the execution result of the function to the user.
The API Gateway is created using the HTTP API type.
The runtime environment for the Lambda function is Python 3.8.
CloudFormation template files
We will build the above configuration using CloudFormation.
Place the CloudFormation template at the following URL.
Template file points
We will cover the key points of each template file to configure this environment.
Grant the Lambda function the permission to execute the function
In fa-005-lambda.yaml, we will define the resources related to Lambda.
First, let’s check the definition of the function itself.
Resources:
Function:
Type: AWS::Lambda::Function
Properties:
Architectures:
- !Ref Architecture
Code:
ZipFile: !Ref ZipFile
FunctionName: !Sub ${Prefix}-function
Handler: !Ref Handler
Runtime: !Ref Runtime
Role: !GetAtt FunctionRole.Arn
Code language: YAML (yaml)The Architectures property is a parameter to specify the underlying processor on which the Lambda function will be executed; as of September 29, 2021, the function can be executed on the Arm-based Graviton2.
It is now possible to configure new and existing functions to run on x86 or Arm/Graviton2 processors.
This choice saves you money in two ways. First, the Graviton2 architecture allows functions to be executed more efficiently. Second, you pay less for the time it takes to execute. In fact, Lambda functions powered by Graviton2 are designed to deliver up to 19% better performance at 20% lower cost.
AWS Graviton2 プロセッサを搭載した AWS Lambda 関数 – Arm で関数を実行し、最大 34% 優れた料金パフォーマンスを実現
This property is set to “x86_64” by default, but in this case, by referring to the variable with the built-in function Fn::Ref and specifying “arm64”, the function can be executed on Graviton2.
In the Code property, configure the settings regarding the code to be executed by the Lambda function. As shown below, you can prepare the code to be executed by the function in three different ways.
To deploy a function defined as a container image, you specify the location of a container image in the Amazon ECR registry. For a .zip file deployment package, you can specify the location of an object in Amazon S3. For Node.js and Python functions, you can specify the function code inline in the template.
AWS::Lambda::Function Code
This time, the code will be written inline in the template file.
For information on how to inline the code to be executed by the Lambda function, please see below.
The code to be executed is as follows
import json
def lambda_handler(event, context):
return {
'statusCode': 200,
'body': json.dumps('Hello form Awstut !')
}
Code language: Python (python)The content is a dictionary type, which simply returns a string in JSON format along with a status code in Python.
The Handler property is a parameter that defines the function to be executed when the function is called. As mentioned above, we have defined the lambda_handler function, so specify the name of the function.
The Runtime property is a parameter that specifies the runtime environment for the function. In this case, we will specify Python 3.8 to run the function.
In the Role property, we need to specify the IAM role associated with the function. In this case, we will define the IAM role as shown below, and specify that it refers to this role.
Resources:
FunctionRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Version: 2012-10-17
Statement:
- Effect: Allow
Action: sts:AssumeRole
Principal:
Service:
- lambda.amazonaws.com
ManagedPolicyArns:
- arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
Code language: YAML (yaml)In the ManagedPolicyArns property, associate the AWS management policy with the IAM role to be created. In this case, we will specify AWSLambdaBasicExecutionRole. The contents of this policy are as follows.
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"logs:CreateLogGroup",
"logs:CreateLogStream",
"logs:PutLogEvents"
],
"Resource": "*"
}
]
}
Code language: JSON / JSON with Comments (json)This is to provide permissions for writing to CloudWatch Logs.
To create an API Gateway, five resources need to be defined
Define the resources related to the API Gateway in fa-005-apigateway.yaml.
When building an environment to execute Lambda through API Gateway, prepare the following five resources.
- API Gateway
- Stage
- Integration
- Route
- Authority for API Gateway to call Lambda functions
Check them in order.
API Gateway
First, check the API Gateway itself.
Resources:
HttpApi:
Type: AWS::ApiGatewayV2::Api
Properties:
Name: !Sub ${Prefix}-HttpApi
Description: HttpApi.
ProtocolType: HTTP
Code language: YAML (yaml)Specify the type of API Gateway to be created in the ProtocolType property.
When creating a RESTful API with API Gateway, you can choose between two types: HTTP API and REST API.
With API Gateway, you can create RESTful APIs using either HTTP APIs or REST APIs. HTTP APIs are the best way to build APIs that do not require API management features. HTTP APIs are optimized for serverless workloads and HTTP backends—they offer up to 71% cost savings and 60% latency reduction compared to REST APIs from API Gateway.
Amazon API Gateway Features
In this case, we will specify “HTTP” for this property and make it an HTTP API type.
Stage
Next, check the Stage.
Resources:
Stage:
Type: AWS::ApiGatewayV2::Stage
Properties:
ApiId: !Ref HttpApi
AutoDeploy: true
StageName: $default
Code language: YAML (yaml)You can prepare stages and build a staging environment for development or production.
An API stage is a logical reference to a lifecycle state of your API (for example,
Working with stages for HTTP APIsdev,prod,beta, orv2). API stages are identified by their API ID and stage name, and they’re included in the URL you use to invoke the API.
This time, you can create a default endpoint by specifying “$default” for the StageName property.
You can create a $default stage that is served from the base of your API’s URL—for example, https://{api_id}.execute-api.{region}.amazonaws.com/.
Working with stages for HTTP APIs
Integration
Then check the integration.
Resources:
Integration:
Type: AWS::ApiGatewayV2::Integration
Properties:
ApiId: !Ref HttpApi
ConnectionType: INTERNET
CredentialsArn: !GetAtt ApiGatewayRole.Arn
IntegrationMethod: POST
IntegrationType: AWS_PROXY
IntegrationUri: !Ref FunctionArn
PayloadFormatVersion: '2.0'
Code language: YAML (yaml)Integration is the middleman between API Gateway itself and resources such as Lambda.
Integrations connect a route to backend resources. HTTP APIs support Lambda proxy, AWS service, and HTTP proxy integrations.
Configuring integrations for HTTP APIs
In this configuration, the API Gateway sends a request from the API Gateway to the Lambda function, which is a backend resource, via the integration, and the response from the Lambda function is returned to the API Gateway.
Specify the API Gateway body in the ApiId property. Specify the aforementioned body resource by referencing it with the Ref function.
The ConnectionType property specifies the connection type to the integration endpoint. This property can be set to “INTERNET” or “VPC_LINK,” but in this case, we will use Lambda outside the VPC as the backend resource, so specify “INTERNET.
The CredentialsArn property is a property related to the permissions required for API Gateway to call the backend resource. Specify the ARN of the IAM role described below.
The IntegrationType property is a parameter that specifies the integration type. If you are using a Lambda function as a backend resource, select Lambda proxy integration.
A Lambda proxy integration enables you to integrate an API route with a Lambda function. When a client calls your API, API Gateway sends the request to the Lambda function and returns the function’s response to the client.
Working with AWS Lambda proxy integrations for HTTP APIs
When using the Lambda proxy integration, specify “AWS_PROXY” for the IntegrationType property.
In the case of Lambda proxy integration, the value to be specified for the IntegrationMethod property is fixed.
For Lambda integrations, you must use the HTTP method of POST for the integration request, according to the specification of the Lambda service action for function invocations.
Set up Lambda proxy integration using the AWS CLI
As described above, specify “POST” for this property.
Specify the backend resource to be called in the IntegrationUri property. In this case, we will be calling a Lambda function, so we will specify the Lambda function described above.
The PayloadFormatVersion property is a parameter that specifies the version of the payload used to mediate between API Gateway and the backend resource. In this case, we will specify the latest version, “2.0”.
Route
Check the route definition.
Resources:
Route:
Type: AWS::ApiGatewayV2::Route
Properties:
ApiId: !Ref HttpApi
RouteKey: 'GET /'
Target: !Sub "integrations/${Integration}"
Code language: YAML (yaml)Route is a resource for tying HTTP methods and URLs to backend resources.
Routes direct incoming API requests to backend resources. Routes consist of two parts: an HTTP method and a resource path—for example,
Working with routes for HTTP APIsGET /pets. You can define specific HTTP methods for your route.
Specify the HTTP method and URL to be associated with the RouteKey property. In this case, we will specify “‘GET /'” to define the route for the endpoint when it is requested to the root URL by GET.
Specify the routing destination in the Target property. The routing destination can be a predefined integration. In this case, we will use the built-in function Fn::Sub and specify it by embedding the ID of the integration resource described earlier.
Authority for API Gateway to call Lambda functions
The CredentialsArn property of the integration resource mentioned above, specify the following IAM roles.
Resources:
ApiGatewayRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Version: 2012-10-17
Statement:
- Effect: Allow
Action: sts:AssumeRole
Principal:
Service:
- apigateway.amazonaws.com
Policies:
- PolicyName: !Sub ${Prefix}-InvokeFunctionPolicy
PolicyDocument:
Version: 2012-10-17
Statement:
- Effect: Allow
Action:
- lambda:InvokeFunction
Resource:
- !Ref FunctionArn
Code language: YAML (yaml)You can authorize the API Gateway to call backend resources in two ways, as follows
The IAM role of apigAwsProxyRole must have policies allowing the apigateway service to invoke Lambda functions… Instead of supplying an IAM role for credentials, you can call the add-permission command to add resource-based permissions.
Set up Lambda proxy integration using the AWS CLI
In this case, we will grant permissions to API Gateway by assigning the former IAM role.
Looking at the content of the policy, we can see that it grants permission to invoke the function by specifying “lambda:InvokeFunction” as Action and the Lambda function mentioned earlier as Resource.
As shown below, you can also use Lambda’s resource-based policy to grant API Gateway the permission to call the function.
Resources:
Permission:
Type: AWS::Lambda::Permission
Properties:
FunctionName: !Ref FunctionName
Action: lambda:InvokeFunction
Principal: apigateway.amazonaws.com
Code language: YAML (yaml)Architecting
Using CloudFormation, we will build this environment and check its actual behavior.
Create CloudFormation stack and check resources in stacks
Create a CloudFormation stack.
For more information on how to create stacks and check each stack, please refer to the following page.
After checking the resources for each stack, the following information is available for the main resources created this time.
- API Gateway ID: io3gltn5gi
- Integration ID: wezv2df
- Lambda function name: fa-005-function
From the AWS Management Console, you can also check the creation status of API Gateway related resources.
First, check the API Gateway itself and its stages.
You can see that the API Gateway itself has been successfully created. You can also see that the stage name “$default” stage has been created. You can now use the API Gateway root URL without including the stage name.
Next, let’s check the integration.
Through the integration, we can see that the Lambda function we created is associated with API Gateway. We can also see that the IAM role with the permissions to call the function is also associated with it.
Finally, let’s check the route.
You can see that the API Gateway root URL is associated with the aforementioned integration. Now, when the API Gateway root URL is accessed, the Lambda function associated with the integration will be called.
Checking Operation: Accessing API Gateway Endpoint
Now that we are ready, let’s access the API Gateway.
The API endpoint created in the API Gateway is a combination of the API ID and region information, as shown below.
API endpoint
Amazon API Gateway concepts
A hostname for an API in API Gateway that is deployed to a specific Region. The hostname is of the form {api-id}.execute-api.{region}.amazonaws.com.
Following the above, the API endpoint created this time will be “https://io3gltn5gi.execute-api.ap-northeast-1.amazonaws.com”.
Let’s actually access it.
$ curl https://<meta charset="utf-8">io3gltn5gi.execute-api.ap-northeast-1.amazonaws.com/
"Hello form Awstut !"
Code language: Bash (bash)The string was returned successfully.
By the way, if you access an undefined route, you will get an error message.
$ curl https://<meta charset="utf-8">io3gltn5gi.execute-api.ap-northeast-1.amazonaws.com/hogehoge
{"message":"Not Found"}
Code language: Bash (bash)As described above, when a user accesses an API endpoint, if the request is for a URL or HTTP method defined in the route, a Lambda function will be executed via the integration. Then, the HTTP response is returned to the user through the integration and API Gateway again.
Summary
We have seen how to build simple serverless applications with Lambda functions and API Gateways, and we have seen that when creating an API Gateway, we need to combine five resources including the main body.
