如何在 Cloudformation 模板中创建可变数量的 EC2 实例资源？

Question

如何根据模板参数在Cloudformation模板中创建可变数量的EC2实例资源？

EC2 API 和管理工具允许启动同一个 AMI 的多个实例，但我找不到使用 Cloudformation 的方法。

Answer 1

同时有很多AWS CloudFormation Sample Templates 可用，其中一些包括启动多个实例，尽管通常同时演示其他功能；例如，AutoScalingKeepAtNSample.template 创建了一个负载平衡、Auto Scaled 示例网站，并被配置为根据此模板摘录为此目的启动 2 个 EC2 实例：

"WebServerGroup": {

    "Type": "AWS::AutoScaling::AutoScalingGroup",
    "Properties": {
        "AvailabilityZones": {
            "Fn::GetAZs": ""
        },
        "LaunchConfigurationName": {
            "Ref": "LaunchConfig"
        },
        "MinSize": "2",
        "MaxSize": "2",
        "LoadBalancerNames": [
            {
                "Ref": "ElasticLoadBalancer"
            }
        ]
    }

},

还有更高级/完整的示例可用，例如Highly Available Web Server with Multi-AZ Amazon RDS database instance and using S3 for storing file content 的 Drupal 模板，当前配置为允许 1-5 个 Web 服务器实例与 Multi-AZ MySQL Amazon RDS 数据库实例通信并在 Elastic Load Balancer 后面运行，后者通过 @987654327 编排 Web 服务器实例@。

Answer 2

我认为最初的海报是这样的：

"Parameters" : {
    "InstanceCount" : {
        "Description" : "Number of instances to start",
        "Type" : "String"
    },

...

"MyAutoScalingGroup" : {
        "Type" : "AWS::AutoScaling::AutoScalingGroup",
        "Properties" : {
        "AvailabilityZones" : {"Fn::GetAZs" : ""},
        "LaunchConfigurationName" : { "Ref" : "MyLaunchConfiguration" },
        "MinSize" : "1",
        "MaxSize" : "2",
        "DesiredCapacity" : **{ "Ref" : "InstanceCount" }**,
        }
    },

...换句话说，从参数中插入初始实例的数量（容量）。

Answer 3

使用Ref 函数。

http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-ref.html

用户定义的变量在配置文件的"Parameters" 部分定义。在配置文件的"Resources" 部分，您可以使用对这些参数的引用来填写值。

{
    "AWSTemplateFormatVersion": "2010-09-09",
    ...
    "Parameters": {
        "MinNumInstances": {
            "Type": "Number",
            "Description": "Minimum number of instances to run.",
            "Default": "1",
            "ConstraintDescription": "Must be an integer less than MaxNumInstances."
        },
        "MaxNumInstances": {
            "Type": "Number",
            "Description": "Maximum number of instances to run.",
            "Default": "5",
            "ConstraintDescription": "Must be an integer greater than MinNumInstances."
        },
        "DesiredNumInstances": {
            "Type": "Number",
            "Description": "Number of instances that need to be running before creation is marked as complete in CloudFormation management console.",
            "Default": "1",
            "ConstraintDescription": "Must be an integer in the range specified by MinNumInstances..MaxNumInstances."
        }
    },
    "Resources": {
        "MyAutoScalingGroup": {
            "Type": "AWS::AutoScaling::AutoScalingGroup",
            "Properties": {
                ...
                "MinSize": { "Ref": "MinNumInstances" },
                "MaxSize": { "Ref": "MaxNumInstances" },
                "DesiredCapacity": { "Ref": "DesiredNumInstances" },
                ...
            },
        },
        ...
    },
    ...
}

在上面的示例中，{ "Ref": ... } 用于将值填充到模板中。在这种情况下，我们提供整数作为 "MinSize" 和 "MaxSize" 的值。

Answer 4

简短的回答是：你不能。您无法获得完全相同的结果（N 个相同的 EC2 实例，未由 Auto Scaling 组绑定）。

从控制台启动多个类似的实例与创建一个具有 N 个实例作为所需容量的 Auto Scaling 组不同。这只是您拥有的一个有用的快捷方式，而不必通过相同的 EC2 创建过程进行 N 次。它被称为“预留”（与预留实例无关）。 Auto Scaling 组是不同的野兽（即使您最终拥有 N 个相同的 EC2 实例）。

您可以：

• 复制 (yuk) 模板中的 EC2 资源
• 使用嵌套模板，该模板将自行创建 EC2，并从您的主堆栈调用它 N 次，每次都使用相同的参数提供给它

问题是，EC2 实例的数量不会是动态的，它不能是参数。

• 使用 CloudFormation 模板的前端，例如对流层，它允许您在函数内编写 EC2 描述，并调用该函数 N 次（我现在选择）。最后，您有一个 CloudFormation 模板可以完成这项工作，但您只编写了一次 EC2 创建代码。 这不是 真正的 CloudFormation 参数，但最终，您会获得 EC2 的动态数量。

Answer 5

AWS::EC2::Instance 资源不支持底层RunInstances API 的MinCount/MaxCount 参数，因此无法通过将参数传递给该 API 的单个副本来创建可变数量的 EC2 实例资源。

根据模板参数在 CloudFormation 模板中创建可变数量的 EC2 实例资源，而不部署 Auto Scaling Group，有两种选择：

1。条件

您可以使用Conditions 根据参数创建可变数量的AWS::EC2::Instance 资源。

这有点冗长（因为您必须使用Fn::Equals），但它确实有效。

这是一个允许用户指定最多 5 个实例的工作示例：

Description: Create a variable number of EC2 instance resources.
Parameters:
  InstanceCount:
    Description: Number of EC2 instances (must be between 1 and 5).
    Type: Number
    Default: 1
    MinValue: 1
    MaxValue: 5
    ConstraintDescription: Must be a number between 1 and 5.
  ImageId:
    Description: Image ID to launch EC2 instances.
    Type: AWS::EC2::Image::Id
    # amzn-ami-hvm-2016.09.1.20161221-x86_64-gp2
    Default: ami-9be6f38c
  InstanceType:
    Description: Instance type to launch EC2 instances.
    Type: String
    Default: m3.medium
    AllowedValues: [ m3.medium, m3.large, m3.xlarge, m3.2xlarge ]
Conditions:
  Launch1: !Equals [1, 1]
  Launch2: !Not [!Equals [1, !Ref InstanceCount]]
  Launch3: !And
  - !Not [!Equals [1, !Ref InstanceCount]]
  - !Not [!Equals [2, !Ref InstanceCount]]
  Launch4: !Or
  - !Equals [4, !Ref InstanceCount]
  - !Equals [5, !Ref InstanceCount]
  Launch5: !Equals [5, !Ref InstanceCount]
Resources:
  Instance1:
    Condition: Launch1
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !Ref ImageId
      InstanceType: !Ref InstanceType
  Instance2:
    Condition: Launch2
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !Ref ImageId
      InstanceType: !Ref InstanceType
  Instance3:
    Condition: Launch3
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !Ref ImageId
      InstanceType: !Ref InstanceType
  Instance4:
    Condition: Launch4
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !Ref ImageId
      InstanceType: !Ref InstanceType
  Instance5:
    Condition: Launch5
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !Ref ImageId
      InstanceType: !Ref InstanceType

1a。带有条件的模板预处理器

作为上述的一种变体，您可以使用像 Ruby 的 Erb 这样的模板预处理器来根据指定的最大值生成上述模板，从而使您的源代码更加紧凑并消除重复：

<%max = 10-%>
Description: Create a variable number of EC2 instance resources.
Parameters:
  InstanceCount:
    Description: Number of EC2 instances (must be between 1 and <%=max%>).
    Type: Number
    Default: 1
    MinValue: 1
    MaxValue: <%=max%>
    ConstraintDescription: Must be a number between 1 and <%=max%>.
  ImageId:
    Description: Image ID to launch EC2 instances.
    Type: AWS::EC2::Image::Id
    # amzn-ami-hvm-2016.09.1.20161221-x86_64-gp2
    Default: ami-9be6f38c
  InstanceType:
    Description: Instance type to launch EC2 instances.
    Type: String
    Default: m3.medium
    AllowedValues: [ m3.medium, m3.large, m3.xlarge, m3.2xlarge ]
Conditions:
  Launch1: !Equals [1, 1]
  Launch2: !Not [!Equals [1, !Ref InstanceCount]]
<%(3..max-1).each do |x|
    low = (max-1)/(x-1) <= 1-%>
  Launch<%=x%>: !<%=low ? 'Or' : 'And'%>
<%  (1..max).each do |i|
      if low && i >= x-%>
  - !Equals [<%=i%>, !Ref InstanceCount]
<%    elsif !low && i < x-%>
  - !Not [!Equals [<%=i%>, !Ref InstanceCount]]
<%    end
    end
  end-%>
  Launch<%=max%>: !Equals [<%=max%>, !Ref InstanceCount]
Resources:
<%(1..max).each do |x|-%>
  Instance<%=x%>:
    Condition: Launch<%=x%>
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !Ref ImageId
      InstanceType: !Ref InstanceType
<%end-%>

要将上述源处理为与 CloudFormation 兼容的模板，请运行：

ruby -rerb -e "puts ERB.new(ARGF.read, nil, '-').result" < template.yml > template-out.yml

为方便起见，这里是为10 variable EC2 instances 生成的输出 YAML 的要点。

2。自定义资源

另一种方法是实现一个Custom Resource，它直接调用RunInstances/TerminateInstances API：

Description: Create a variable number of EC2 instance resources.
Parameters:
  InstanceCount:
    Description: Number of EC2 instances (must be between 1 and 10).
    Type: Number
    Default: 1
    MinValue: 1
    MaxValue: 10
    ConstraintDescription: Must be a number between 1 and 10.
  ImageId:
    Description: Image ID to launch EC2 instances.
    Type: AWS::EC2::Image::Id
    # amzn-ami-hvm-2016.09.1.20161221-x86_64-gp2
    Default: ami-9be6f38c
  InstanceType:
    Description: Instance type to launch EC2 instances.
    Type: String
    Default: m3.medium
    AllowedValues: [ m3.medium, m3.large, m3.xlarge, m3.2xlarge ]
Resources:
  EC2Instances:
    Type: Custom::EC2Instances
    Properties:
      ServiceToken: !GetAtt EC2InstancesFunction.Arn
      ImageId: !Ref ImageId
      InstanceType: !Ref InstanceType
      MinCount: !Ref InstanceCount
      MaxCount: !Ref InstanceCount
  EC2InstancesFunction:
    Type: AWS::Lambda::Function
    Properties:
      Handler: index.handler
      Role: !GetAtt LambdaExecutionRole.Arn
      Code:
        ZipFile: !Sub |
          var response = require('cfn-response');
          var AWS = require('aws-sdk');
          exports.handler = function(event, context) {
            var physicalId = event.PhysicalResourceId || 'none';
            function success(data) {
              return response.send(event, context, response.SUCCESS, data, physicalId);
            }
            function failed(e) {
              return response.send(event, context, response.FAILED, e, physicalId);
            }
            var ec2 = new AWS.EC2();
            var instances;
            if (event.RequestType == 'Create') {
              var launchParams = event.ResourceProperties;
              delete launchParams.ServiceToken;
              ec2.runInstances(launchParams).promise().then((data)=> {
                instances = data.Instances.map((data)=> data.InstanceId);
                physicalId = instances.join(':');
                return ec2.waitFor('instanceRunning', {InstanceIds: instances}).promise();
              }).then((data)=> success({Instances: instances})
              ).catch((e)=> failed(e));
            } else if (event.RequestType == 'Delete') {
              if (physicalId == 'none') {return success({});}
              var deleteParams = {InstanceIds: physicalId.split(':')};
              ec2.terminateInstances(deleteParams).promise().then((data)=>
                ec2.waitFor('instanceTerminated', deleteParams).promise()
              ).then((data)=>success({})
              ).catch((e)=>failed(e));
            } else {
              return failed({Error: "In-place updates not supported."});
            }
          };
      Runtime: nodejs4.3
      Timeout: 300
  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Principal: {Service: [lambda.amazonaws.com]}
          Action: ['sts:AssumeRole']
      Path: /
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
      - PolicyName: EC2Policy
        PolicyDocument:
          Version: '2012-10-17'
          Statement:
            - Effect: Allow
              Action:
              - 'ec2:RunInstances'
              - 'ec2:DescribeInstances'
              - 'ec2:DescribeInstanceStatus'
              - 'ec2:TerminateInstances'
              Resource: ['*']
Outputs:
  Instances:
    Value: !Join [',', !GetAtt EC2Instances.Instances]