Secrets ManagerとParameter Store

コードにシークレットを保存する問題

# Anti-pattern: secrets in code (NEVER do this)
# db_password = 'supersecret123'
# api_key = 'sk-abc123def456'

# Best practice: retrieve at runtime
import boto3

client = boto3.client('secretsmanager', region_name='us-east-1')
response = client.get_secret_value(SecretId='prod/myapp/db-password')
password = response['SecretString']  # fresh value, always current

AWS Secrets Manager の概要

# Create a secret in Secrets Manager
aws secretsmanager create-secret \
  --name 'prod/myapp/database' \
  --description 'Production MySQL credentials' \
  --secret-string '{"username":"admin","password":"changeme123","host":"mydb.rds.amazonaws.com","port":3306,"dbname":"orders"}'

# Retrieve the secret (by application)
aws secretsmanager get-secret-value \
  --secret-id 'prod/myapp/database' \
  --query 'SecretString' \
  --output text | python3 -c 'import sys,json; s=json.load(sys.stdin); print(s["password"])'

Secrets Managerによる自動ローテーション

# Enable automatic rotation for RDS secret
aws secretsmanager rotate-secret \
  --secret-id 'prod/myapp/database' \
  --rotation-rules AutomaticallyAfterDays=30 \
  --rotation-lambda-arn arn:aws:lambda:us-east-1:123:function:SecretsManagerRDSMySQLRotationSingleUser

# AWS provides pre-built rotation Lambda functions for:
# - RDS MySQL/PostgreSQL/MariaDB/Oracle/SQL Server
# - DocumentDB
# - Redshift
# - Custom: write your own Lambda for other services

# Application code: always call GetSecretValue, never cache long-term

シークレットのローカルキャッシュ

# Python: Secrets Manager caching client
# pip install aws-secretsmanager-caching

from botocore.session import get_session
from aws_secretsmanager_caching import SecretCache, SecretCacheConfig

client = get_session().create_client('secretsmanager')
cache = SecretCache(
    config=SecretCacheConfig(secret_refresh_interval=3600),  # cache 1 hour
    client=client
)

# Returns cached value unless refresh interval expired
secret = cache.get_secret_string('prod/myapp/database')

AWS Systems Manager Parameter Store

# Create Parameter Store parameters
aws ssm put-parameter \
  --name '/prod/myapp/db-host' \
  --value 'mydb.cluster-abc.us-east-1.rds.amazonaws.com' \
  --type String

aws ssm put-parameter \
  --name '/prod/myapp/db-password' \
  --value 'mysecretpassword' \
  --type SecureString \
  --key-id alias/my-kms-key

# Retrieve parameter
aws ssm get-parameter \
  --name '/prod/myapp/db-password' \
  --with-decryption \
  --query 'Parameter.Value' --output text

Parameter Storeの階層構造とIAM

# Parameter hierarchy
/prod/payment-service/db-password
/prod/payment-service/stripe-api-key
/prod/order-service/db-password
/prod/order-service/redis-url
/staging/payment-service/db-password

# IAM policy: payment-service Lambda can ONLY read its params
{
  'Effect': 'Allow',
  'Action': ['ssm:GetParameter', 'ssm:GetParameters', 'ssm:GetParametersByPath'],
  'Resource': 'arn:aws:ssm:us-east-1:123:parameter/prod/payment-service/*'
}

# Get all parameters for an app at once
aws ssm get-parameters-by-path \
  --path '/prod/payment-service/' \
  --with-decryption --recursive

Secrets ManagerとParameter Store：使い分け

# Usage comparison:
# Secrets Manager:
#   Cost: $0.40/secret/month
#   Rotation: Automatic (RDS, custom Lambda)
#   Cross-account: Yes
#   Best for: Database passwords, API keys, OAuth tokens

# Parameter Store:
#   Cost: Free (standard) / $0.05/month (advanced)
#   Rotation: Manual only
#   Cross-account: No (use Secrets Manager)
#   Best for: Config values, feature flags, non-rotating secrets

LambdaとECSとの統合

# ECS task definition: inject secret as environment variable
{
  'containerDefinitions': [{
    'name': 'api',
    'image': 'my-api:latest',
    'secrets': [
      {
        'name': 'DB_PASSWORD',
        'valueFrom': 'arn:aws:secretsmanager:us-east-1:123:secret:prod/myapp/database:password::'
      },
      {
        'name': 'API_KEY',
        'valueFrom': '/prod/myapp/api-key'
      }
    ]
  }]
}
# Application reads DB_PASSWORD from env var
# ECS injects the current secret value at task start

EC2 AMI IDのParameter Storeでの管理

# Get AWS public AMI ID from Parameter Store
aws ssm get-parameter \
  --name '/aws/service/ami-amazon-linux-latest/al2023-ami-kernel-default-x86_64' \
  --query 'Parameter.Value' --output text

# CloudFormation: reference public AMI parameter
Parameters:
  LatestAmiId:
    Type: 'AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>'
    Default: '/aws/service/ami-amazon-linux-latest/al2023-ami-kernel-default-x86_64'

Resources:
  MyEC2:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !Ref LatestAmiId

シークレットの監査とコンプライアンス

# CloudTrail metric filter: alert on unexpected secret access
aws logs put-metric-filter \
  --log-group-name CloudTrail/management-events \
  --filter-name 'SecretAccessOutsideHours' \
  --filter-pattern '{ $.eventSource = "secretsmanager.amazonaws.com" && $.eventName = "GetSecretValue" && $.userAgent != "lambda.amazonaws.com" }' \
  --metric-transformations \
    metricName=UnexpectedSecretAccess,metricNamespace=Security,metricValue=1

# Then create CloudWatch alarm on this metric
# Alert fires when non-Lambda principal accesses secrets

クロスアカウントでのシークレット共有

# Secret resource policy: allow cross-account access
aws secretsmanager put-resource-policy \
  --secret-id 'prod/shared/rds-password' \
  --resource-policy '{
    "Statement": [{
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::999999999999:role/AppRole"
      },
      "Action": "secretsmanager:GetSecretValue",
      "Resource": "*"
    }]
  }'

# KMS key policy must also allow account 999999999999
# IAM policy in 999999999999 must allow GetSecretValue on ARN

クイックチェック

レッスンのまとめ