AWS Step Functionsで非同期ワークフローを設計する方法｜ステートマシンでLambdaをオーケストレーションする実践パターン

この記事のポイント

・ステートマシンはTask・Parallel・Wait・Choiceなど8種のStateで構成される
・直列連鎖は "Next" で次Stateを指定し、"End:true" で終端を定義する
・Parallel Stateで複数Lambdaを並列実行しWall Clockを短縮できる
・Retry/Catchでエラーハンドリングを宣言的に定義、コード修正不要

{
  "Comment": "ワークフローの説明（省略可）",
  "StartAt": "最初のState名",
  "States": {
    "最初のState名": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:リージョン:アカウントID:function:FunctionName",
      "Next": "次のState名"
    },
    "次のState名": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:リージョン:アカウントID:function:FunctionName2",
      "End": true
    }
  }
}

# state-machine.json
{
  "Comment": "EC2スナップショット自動化ワークフロー",
  "StartAt": "CreateSnapshot",
  "States": {
    "CreateSnapshot": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:ap-northeast-1:1234XXXX89012:function:CreateSnapshot",
      "ResultPath": "$.snapshotResult",
      "Next": "TagSnapshot"
    },
    "TagSnapshot": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:ap-northeast-1:1234XXXX89012:function:TagSnapshot",
      "ResultPath": "$.tagResult",
      "Next": "SendNotification"
    },
    "SendNotification": {
      "Type": "Task",
      "Resource": "arn:aws:states:::sns:publish",
      "Parameters": {
        "TopicArn": "arn:aws:sns:ap-northeast-1:1234XXXX89012:backup-notification",
        "Message.$": "States.Format('スナップショット {} の作成が完了しました', $.snapshotResult.snapshotId)"
      },
      "End": true
    }
  }
}

# Step Functionsが引き受けるIAMロールの信頼ポリシーを定義
cat > trust-policy.json << 'EOF'
{
  "Version": "2012-10-17",
  "Statement": [{
    "Effect": "Allow",
    "Principal": {"Service": "states.amazonaws.com"},
    "Action": "sts:AssumeRole"
  }]
}
EOF

# IAMロールを作成
aws iam create-role   --role-name StepFunctionsExecutionRole   --assume-role-policy-document file://trust-policy.json

# ステートマシンを作成
aws stepfunctions create-state-machine   --name "ec2-backup-workflow"   --role-arn "arn:aws:iam::1234XXXX89012:role/StepFunctionsExecutionRole"   --definition file://state-machine.json   --type STANDARD   --region ap-northeast-1

# ワークフローの実行を開始する
aws stepfunctions start-execution   --state-machine-arn "arn:aws:states:ap-northeast-1:1234XXXX89012:stateMachine:ec2-backup-workflow"   --input '{"instanceId": "i-0a1b2c3d4e5f67890"}'   --region ap-northeast-1

{
    "executionArn": "arn:aws:states:ap-northeast-1:1234XXXX89012:execution:ec2-backup-workflow:550e8400-e29b-41d4",
    "startDate": "2026-09-10T10:00:00.123Z"
}

aws stepfunctions describe-execution   --execution-arn "arn:aws:states:ap-northeast-1:1234XXXX89012:execution:ec2-backup-workflow:550e8400-e29b-41d4"

{
    "executionArn": "arn:aws:states:ap-northeast-1:1234XXXX89012:execution:ec2-backup-workflow:550e8400-e29b-41d4",
    "stateMachineArn": "arn:aws:states:ap-northeast-1:1234XXXX89012:stateMachine:ec2-backup-workflow",
    "name": "550e8400-e29b-41d4",
    "status": "SUCCEEDED",
    "startDate": "2026-09-10T10:00:00.123Z",
    "stopDate": "2026-09-10T10:00:04.876Z",
    "input": "{"instanceId": "i-0a1b2c3d4e5f67890"}",
    "output": "{"snapshotResult":{"snapshotId":"snap-0abc123def456789"},"tagResult":{"success":true}}"
}

{
  "Comment": "マルチリージョン同時バックアップ確認",
  "StartAt": "CheckAllRegions",
  "States": {
    "CheckAllRegions": {
      "Type": "Parallel",
      "Branches": [
        {
          "StartAt": "CheckTokyo",
          "States": {
            "CheckTokyo": {
              "Type": "Task",
              "Resource": "arn:aws:lambda:ap-northeast-1:1234XXXX89012:function:CheckBackup",
              "Parameters": {"region": "ap-northeast-1"},
              "End": true
            }
          }
        },
        {
          "StartAt": "CheckOsaka",
          "States": {
            "CheckOsaka": {
              "Type": "Task",
              "Resource": "arn:aws:lambda:ap-northeast-3:1234XXXX89012:function:CheckBackup",
              "Parameters": {"region": "ap-northeast-3"},
              "End": true
            }
          }
        }
      ],
      "Next": "AggregateResults"
    },
    "AggregateResults": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:ap-northeast-1:1234XXXX89012:function:AggregateResults",
      "End": true
    }
  }
}

"CreateSnapshot": {
  "Type": "Task",
  "Resource": "arn:aws:lambda:ap-northeast-1:1234XXXX89012:function:CreateSnapshot",
  "Retry": [
    {
      "ErrorEquals": ["Lambda.ServiceException", "Lambda.TooManyRequestsException"],
      "IntervalSeconds": 2,
      "MaxAttempts": 3,
      "BackoffRate": 2.0,
      "JitterStrategy": "FULL"
    }
  ],
  "Next": "TagSnapshot"
}

"CreateSnapshot": {
  "Type": "Task",
  "Resource": "arn:aws:lambda:ap-northeast-1:1234XXXX89012:function:CreateSnapshot",
  "Retry": [
    {
      "ErrorEquals": ["Lambda.TooManyRequestsException"],
      "IntervalSeconds": 2,
      "MaxAttempts": 3,
      "BackoffRate": 2.0
    }
  ],
  "Catch": [
    {
      "ErrorEquals": ["States.ALL"],
      "Next": "HandleError",
      "ResultPath": "$.error"
    }
  ],
  "Next": "TagSnapshot"
},
"HandleError": {
  "Type": "Task",
  "Resource": "arn:aws:lambda:ap-northeast-1:1234XXXX89012:function:NotifyFailure",
  "End": true
}