BFF（Backend for Frontend）を基礎から理解する – AWSでの実装付き解説 –

bff-sam/
├── template.yaml              # SAM テンプレートファイル（CloudFormation）
├── events/
│   └── event.json             # テスト用のリクエスト（ローカルテスト用）
├── src/
│   └── app.js                 # Lambda ハンドラ関数（BFFロジック）
├── package.json               # Node.js パッケージ定義（axiosなどを管理）
└── README.md                  # プロジェクト説明（任意）

% gh repo create bff-on-aws --public --clone
✓ Created repository XXXXX/bff-on-aws on GitHub
  https://github.com/XXXXX/bff-on-aws
% gh repo view XXXXX/bff-on-aws
XXXXX/bff-on-aws
No description provided

This repository does not have a README

View this repository on GitHub: https://github.com/XXXXX/bff-on-aws
% 

const axios = require("axios");

exports.handler = async (event) => {
  try {
    const [postsRes, usersRes] = await Promise.all([
      axios.get("https://jsonplaceholder.typicode.com/posts"),
      axios.get("https://jsonplaceholder.typicode.com/users"),
    ]);

    //
    console.log("postsRes sample:", postsRes.data.slice(0, 1));
    console.log("usersRes sample:", usersRes.data.slice(0, 1));

    const usersMap = new Map(usersRes.data.map(user => [user.id, user.name]));

    const combined = postsRes.data.map(post => ({
      id: post.id,
      author: usersMap.get(post.userId) || "Unknown",
    }));

    return {
      statusCode: 200,
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify(combined)
    };
  } catch (error) {
    console.error(" Lambda error:", error);
    return {
      statusCode: 500,
      body: JSON.stringify({ message: "Internal server error" })
    };
  }
};

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
  AWS SAM template for BFF (Backend for Frontend) demo.
  Aggregates /posts and /users from JSONPlaceholder.

Globals:
  Function:
    Timeout: 10
    Runtime: nodejs18.x
    Architectures:
      - x86_64

Resources:
  BffFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: app.handler
      CodeUri: src/
      Description: BFF Lambda Function that aggregates posts and users
      MemorySize: 128
      Events:
        Api:
          Type: Api
          Properties:
            Path: /posts-with-users
            Method: get
            Auth:
              AuthorizationType: NONE      

Outputs:
  BffApiUrl:
    Description: "API Gateway endpoint URL for BFF function"
    Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/posts-with-users"

bff-on-aws % cd src       
src % npm init -y

Wrote to /Users/XXXXXX/Documents/cursor/bff-on-aws/src/package.json:

{
  "name": "src",
  "version": "1.0.0",
  "main": "handler.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "axios": "^1.8.4"
  },
  "devDependencies": {},
  "description": ""
}



src % npm install axios

up to date, audited 24 packages in 824ms

6 packages are looking for funding
  run `npm fund` for details

found 0 vulnerabilities
src % 

src % cd ..
bff-on-aws % sam build

        SAM CLI now collects telemetry to better understand customer needs.

        You can OPT OUT and disable telemetry collection by setting the
        environment variable SAM_CLI_TELEMETRY=0 in your shell.
        Thanks for your help!

        Learn More: https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-telemetry.html

Building codeuri: /Users/XXXXXX/Documents/cursor/bff-on-aws/src runtime: nodejs18.x architecture: x86_64 functions: BffFunction                    
package.json file not found. Continuing the build without dependencies.                                                                               
 Running NodejsNpmBuilder:CopySource                                                                                                                  

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

SAM CLI update available (1.136.0); (1.134.0 installed)
To download: https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-install.html
bff-on-aws % ls -lR .aws-sam
total 8
drwxr-xr-x@ 4 XXXXX  YYYYY  128  3 30 16:09 build
-rw-r--r--@ 1 XXXXX  YYYYY  348  3 30 16:09 build.toml

.aws-sam/build:
total 8
drwxr-xr-x@ 3 XXXXX  YYYYY   96  3 30 16:09 BffFunction
-rw-r--r--@ 1 XXXXX  YYYYY  895  3 30 16:09 template.yaml

.aws-sam/build/BffFunction:
total 8
-rw-r--r--@ 1 XXXXX  YYYYY  995  3 30 16:01 handler.js
bff-on-aws % 

bff-on-aws % aws sso login --sso-session XXXXXXX
bff-on-aws % export AWS_PROFILE=XXXXXXX
bff-on-aws % aws sts get-caller-identity        
{
    "UserId": "XXXXXX",
    "Account": "XXXXXX",
    "Arn": "arn:aws:sts::XXXXXX:assumed-role/XXXXXX/XXXXX"
}
bff-on-aws % 

bff-on-aws % sam deploy --guided                       

Configuring SAM deploy
======================

        Looking for config file [samconfig.toml] :  Not found

        Setting default arguments for 'sam deploy'
        =========================================
        Stack Name [sam-app]: bff-sam-demo
        AWS Region [ap-northeast-1]:               
        #Shows you resources changes to be deployed and require a 'Y' to initiate deploy
        Confirm changes before deploy [y/N]: y
        #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]: y
        #Preserves the state of previously provisioned resources when an operation fails
        Disable rollback [y/N]: N
        BffFunction has no authentication. Is this okay? [y/N]: y
        Save arguments to configuration file [Y/n]: Y
        SAM configuration file [samconfig.toml]: 
        SAM configuration environment [default]: 

        Looking for resources needed for deployment:
        Creating the required resources...
        Successfully created!

bff-on-aws % curl https://XXXXXX.execute-api.ap-northeast-1.amazonaws.com/Prod/posts-with-users |jq
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  3843  100  3843    0     0   5315      0 --:--:-- --:--:-- --:--:--  5315
[
  {
    "id": 1,
    "author": "Leanne Graham"
  },
  {
    "id": 2,
    "author": "Leanne Graham"
  },
  {
    "id": 3,
    "author": "Leanne Graham"
  },

・・・・・省略・・・・・ 

  {
    "id": 99,
    "author": "Clementina DuBuque"
  },
  {
    "id": 100,
    "author": "Clementina DuBuque"
  }
]
bff-on-aws % 

# Node.js dependencies
node_modules/
package-lock.json
npm-debug.log*

# SAM build artifacts
.aws-sam/
.env
*.template.yaml  # ビルド後に生成される template

# VSCode
.vscode/

# macOS system files
.DS_Store

# Logs
logs/
*.log

# SAM config
samconfig.toml

bff-on-aws % tree -L 2           
.
├── README.md
├── samconfig.toml
├── src
│   ├── app.js
│   ├── node_modules
│   ├── package-lock.json
│   └── package.json
└── template.yml

3 directories, 6 files
bff-on-aws % 

% git push origin main