DynamoDB w / Serverless，使用Fn :: GetRef引用全局二级索引

Question

我有一个用DynamoDB表定义的API /服务。我有几个索引（定义为全局二级索引）来支持几个查询。我设计了具有GSI定义的表，以及看起来像正确的查询的表。但是，在进行查询时出现此异常：

{ AccessDeniedException: User: arn:aws:sts::OBSCURED:assumed-role/chatroom-application-dev-us-east-1-lambdaRole/chatroom-application-dev-getRoomMessages is not authorized to perform: dynamodb:Query on resource: arn:aws:dynamodb:us-east-1:OBSCURED:table/messages-table-dev/index/roomIndex
at Request.extractError (/var/task/node_modules/aws-sdk/lib/protocol/json.js:48:27)
at Request.callListeners (/var/task/node_modules/aws-sdk/lib/sequential_executor.js:105:20)
at Request.emit (/var/task/node_modules/aws-sdk/lib/sequential_executor.js:77:10)
at Request.emit (/var/task/node_modules/aws-sdk/lib/request.js:683:14)
at Request.transition (/var/task/node_modules/aws-sdk/lib/request.js:22:10)
at AcceptorStateMachine.runTo (/var/task/node_modules/aws-sdk/lib/state_machine.js:14:12)
at /var/task/node_modules/aws-sdk/lib/state_machine.js:26:10
at Request.<anonymous> (/var/task/node_modules/aws-sdk/lib/request.js:38:9)
at Request.<anonymous> (/var/task/node_modules/aws-sdk/lib/request.js:685:12)
at Request.callListeners (/var/task/node_modules/aws-sdk/lib/sequential_executor.js:115:18)
message: 'User: arn:aws:sts::OBSCURED:assumed-role/chatroom-application-dev-us-east-1-lambdaRole/chatroom-application-dev-getRoomMessages is not authorized to perform: dynamodb:Query on resource: arn:aws:dynamodb:us-east-1:OBSCURED:table/messages-table-dev/index/roomIndex',
code: 'AccessDeniedException',
time: 2018-06-02T22:05:46.110Z,
requestId: 'OBSCURED',
statusCode: 400,
retryable: false,
retryDelay: 30.704899664776054 }

在异常的最上方，它说我的getRoomMessages方法is not authorized to perform: dynamodb:Query on resource:的ARN并显示全局二级索引的ARN。

显然，我需要定义策略以授予访问全局二级索引的权限。但这还不清楚。我已经看到了有关DynamoDB的其他StackOverflow问题，他们抱怨文档零散，很难找到任何东西。我必须同意。“碎片化”一词太温和了。

我正在使用无服务器框架。本provider部分显示此策略/角色定义：

provider:
  name: aws
  runtime: nodejs8.10
  stage: dev
  region: us-east-1
  iamRoleStatements:
    - Effect: Allow
      Action:
        - dynamodb:Query
        - dynamodb:Scan
        - dynamodb:GetItem
        - dynamodb:PutItem
        - dynamodb:UpdateItem
        - dynamodb:DeleteItem
      Resource:
        - { "Fn::GetAtt": ["MessagesDynamoDBTable", "Arn" ] }
        - { "Fn::GetAtt": ["#roomIndex", "Arn" ] }
        - { "Fn::GetAtt": ["#userIndex", "Arn" ] }
  environment:
    MESSAGES_TABLE: ${self:custom.tableName}

在本Resource节中，我相信我应该列出声明其权限的资源。第一个引用整个表。我刚刚添加了最后两个，并引用了索引。

编辑：当我运行serverless deploy以下消息时打印：

The CloudFormation template is invalid: Template error: instance of Fn::GetAtt references undefined resource #roomIndex

我为此尝试了几种变体，只是得到了相同的错误。归结为- 我如何serverless.yml使用Cloudfront语法获取索引的ARN。由于存在异常，因此ARN确实存在。

DynamoDB表定义：

resources:
  Resources:
    MessagesDynamoDBTable:
      Type: AWS::DynamoDB::Table
      Properties:
        AttributeDefinitions:
          - AttributeName: messageId
            AttributeType: S
          - AttributeName: room
            AttributeType: S
          - AttributeName: userId
            AttributeType: S
        KeySchema:
          - AttributeName: messageId
            KeyType: HASH
        GlobalSecondaryIndexes:
          - IndexName: roomIndex
            KeySchema:
              - AttributeName: room
                KeyType: HASH
            Projection:
              ProjectionType: ALL
            ProvisionedThroughput:
              ReadCapacityUnits: 1
              WriteCapacityUnits: 1
          - IndexName: userIndex
            KeySchema:
              - AttributeName: userId
                KeyType: HASH
            Projection:
              ProjectionType: ALL
            ProvisionedThroughput:
              ReadCapacityUnits: 1
              WriteCapacityUnits: 1
        ProvisionedThroughput:
          ReadCapacityUnits: 1
          WriteCapacityUnits: 1
        TableName: ${self:custom.tableName}

使用的查询对应于上述异常：

{
    "TableName": "messages-table-dev",
    "IndexName": "roomIndex",
    "KeyConditionExpression": "#roomIndex = :room",
    "ExpressionAttributeNames": {
        "#roomIndex": "room"
    },
    "ExpressionAttributeValues": {
        ":room": {
            "S": "everyone"
        }
    }
}

生成查询的Lambda函数代码段：

app.get('/messages/room/:room', (req, res) => {
    const params = {
        TableName: MESSAGES_TABLE,
        IndexName: "roomIndex",
        KeyConditionExpression: '#roomIndex = :room',
        ExpressionAttributeNames: { '#roomIndex': 'room' },
        ExpressionAttributeValues: {
            ":room": { S: `${req.params.room}` }
        },
    };
    console.log(`QUERY ROOM ${JSON.stringify(params)}`);
    dynamoDb.query(params, (error, result) => {
        if (error) {
            console.log(error);
            res.status(400).json({ error: 'Could not get messages' });
        } else {
            res.json(result.Items);
        }
    });
});

Answer 1

我发现比jake.lang发布的答案更好。编辑：我没有看到他的第二条评论，他在其中提出了以下建议。

正如他指出的那样，他的说法是错误的，因为ARN可以出于正当理由进行更改。但是，由于全局二级索引的ARN会将“ / INDEXNAME”附加到表的ARN上，因此出现了解决方案。这意味着该策略声明可以是：

iamRoleStatements:
  - Effect: Allow
    Action:
      - dynamodb:Query
      - dynamodb:Scan
      - dynamodb:GetItem
      - dynamodb:PutItem
      - dynamodb:UpdateItem
      - dynamodb:DeleteItem
    Resource:
      - { "Fn::GetAtt": ["MessagesDynamoDBTable", "Arn" ] }
      - { "Fn::Join": [ "/", [ 
          { "Fn::GetAtt": ["MessagesDynamoDBTable", "Arn" ] }, "index", "roomIndex" 
        ]]}
      - { "Fn::Join": [ "/", [
          { "Fn::GetAtt": ["MessagesDynamoDBTable", "Arn" ] }, "index", "userIndex" 
        ]]}

“ Fn :: Join”位来自CloudFormation，并且是“ join”操作。它需要一个字符串数组，并使用第一个参数将它们连接起来。因此，计算此策略声明中所需的ARN是一种相当复杂且过于复杂的方法。

有关文档，请参阅：https : //docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-join.html

Answer 2

而不是Fn::Join您可以使用!Sub "${MessagesDynamoDBTable.Arn}"，它更简单。此外，如果您想访问所有索引（这通常是我的情况），那么这/index/*就是您所需要的。

例子：

...
      Policies:
        - Version: "2012-10-17"
          Statement:
            - Effect: Allow
              Action:
                - dynamodb:Query
              Resource:
                - !Sub "${MessagesDynamoDBTable.Arn}"
                - !Sub "${MessagesDynamoDBTable.Arn}/index/*"
...