基于 Tag 驱动的 EBS 类型优化 CloudFormation 模板_语言 & 开发_亚马逊云科技 (Amazon Web Services）

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需求背景

企业中用于做报表的数据库服务器只是在每天的某个时间点需要大规模的磁盘 IO 操作，持续时间大约几个小时，如果按照高峰时期的磁盘 IO 需求来设定 EBS 卷的类型，需要 IOPS 为 10000 的 io1 卷。而按照平时大多数时候的磁盘 IO 水平来看，gp2 类型的磁盘已经可以满足要求。为了能够做到物尽其用，节省成本，在 IO 高峰时候使用 io1 卷，而平时使用 gp2 卷会是一个理想的安排。

方案概述

为了能够简化实际操作过程的复杂度，方案采用通过定义 EBS 卷的 Tag 来触发对应的 Lambda 功能从而实现定期更改 EBS 卷的类型。

首先，用户需要启动 CloudTrail, 并将 CloudTrail 与 CloudWatch 集成，本文假设 CloudWatch Log Group 的名字是 CloudTrail/DefaultLogGroup。

我们将通过 CloudTrail 来捕捉用户对 EBS 卷的操作，如果用户创建、更改或者删除名字为 ChangeEBSType 的 Tag，就会触发一个 Lambda 功能调用。判断触发条件是通过定义 Log Group 的 Filter 实现的，Filter 的定义如下：

  "SubscriptionFilter": {
      "Type": "AWS::Logs::SubscriptionFilter",
      "Properties": {
        "LogGroupName": {
          "Ref": "CloudTrailLogGroup"
        },
        "FilterPattern": "{($.requestParameters.tagSet.items[0].key = \"ChangeEBSType\") && ($.eventName = *Tags) && ($.requestParameters.tagSet.items[0].value!= \"\" ) && ($.requestParameters.resourcesSet.items[0].resourceId = \"vol*\")}",
        "DestinationArn": {
          "Fn::GetAtt": ["EBSChangeScheduler", "Arn"]
        }
      }
    }

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当 Filter 的条件满足后，就会触发名字为 EBSChangeScheduler 的 Lambda 功能，这个 Lambda 程序将根据 Tag 的输入值，调用另一个 CloudFormation 模板以部署对应的 CloudWatch Event Rules（规定什么时间对 EBS 卷的类型进行修改）和 Lambda 功能（change-ebs-type 完成 EBS 卷的类型修改）。

整个方案的流程如下：

调用现有的 CloudFormation 模板并创建对应 Stack 的 Lambda（EBSChangeScheduler.py）功能的示例代码如下：

import json
import zlib
import boto3
import botocore
import base64
import string

TemplateURL = ""

def get_cloudtrail_event(event):
    data = base64.b64decode(event['awslogs']['data'])
    data = zlib.decompress(data, 16 + zlib.MAX_WBITS)
    cloudtrail_event = json.loads(data)
    return cloudtrail_event

def get_message_from_cloudtrail_event(log_event):
    old_str = '\\"'
    new_str = '"'
    message = log_event['message']
    message = message.replace(old_str, new_str)
    return json.loads(message)

def create_cloudformation(stack_name, parameter1, parameter2, volume_id, client):
    print ("Create cloudformation stack: %s" % stack_name)
    try:
        response = client.create_stack(StackName=stack_name, TemplateURL=TemplateURL, Parameters=[
            {'ParameterKey': 'TargetEBSVolumeInfo', 'ParameterValue': parameter1}, {'ParameterKey': 'ScheduleExpression', 'ParameterValue': parameter2}, ], Capabilities=['CAPABILITY_IAM'])
    except Exception as ex:
        print ex.message

def update_cloudformation(stack_name, parameter1, parameter2, volume_id, client):
    print ("Update cloudformation stack: %s" % stack_name)
    try:
        response = client.update_stack(StackName=stack_name, UsePreviousTemplate=True, Parameters=[
            {'ParameterKey': 'TargetEBSVolumeInfo', 'ParameterValue': parameter1}, {'ParameterKey': 'ScheduleExpression', 'ParameterValue': parameter2}, ], Capabilities=['CAPABILITY_IAM'])
    except botocore.exceptions.ClientError as ex:
        error_message = ex.response['Error']['Message']
        if error_message == 'No updates are to be performed.':
            print("No changes")
        else:
            raise

def check_valid_stack(stack_name, client):
    try:
        response = client.describe_stacks()
    except Exception as ex:
        print ex.message
    for stack in response['Stacks']:
        if stack_name in stack['StackName']:
            return True

def build_ebs_volume_change_schedule(stack_name, target_schedule, volume_id, client):
    target_type = target_schedule.split(':')
    parameter1 = volume_id + ":" + target_type[0] + ":" + target_type[1]
    parameter2 = "cron" + target_type[2]
    print ("CloudForamtion template parameters:{},{}".format(
        parameter1, parameter2))
    print ("Volume %s will be changed to %s, IOPS is %s" %
           (volume_id, target_type[0], target_type[1]))
    print ("This task will be executed based on %s" % target_type[2])
    if check_valid_stack(stack_name, client):
        try:
            cloudformation = boto3.resource('cloudformation')
            try:
                stack = cloudformation.Stack(stack_name)
            except Exception as ex:
                print ex.message
            stack_status = stack.stack_status
            print ("Stack (%s) status: %s" % (stack_name, stack_status))
            if stack_status == "ROLLBACK_COMPLETE" or stack_status == "ROLLBACK_FAILED" or stack_status == "DELETE_FAILED":
                try:
                    response = client.delete_stack(StackName=stack_name)
                    waiter = client.get_waiter('stack_delete_complete')
                    waiter.wait(StackName=stack_name)
                except Exception as ex:
                    print ex.message
            if stack_status == "CREATE_IN_PROGRESS":
                waiter = client.get_waiter('stack_create_complete')
                waiter.wait(StackName=stack_name)
            if stack_status == "DELETE_IN_PROGRESS":
                waiter = client.get_waiter('stack_delete_complete')
                waiter.wait(StackName=stack_name)
            if stack_status == "UPDATE_IN_PROGRESS":
                waiter = client.get_waiter('stack_update_complete')
                waiter.wait(StackName=stack_name)
        except Exception as ex:
            print ex.message
    if check_valid_stack(stack_name, client):
        update_cloudformation(stack_name, parameter1, parameter2,
                              volume_id, client)
        waiter = client.get_waiter('stack_update_complete')
    else:
        create_cloudformation(stack_name, parameter1, parameter2,
                              volume_id, client)
        waiter = client.get_waiter('stack_create_complete')

def delete_ebs_volume_change_schedule(volume_id, client):
    response = client.describe_stacks()
    for stack in response['Stacks']:
        if volume_id in stack['StackName']:
            try:
                print("Delete cloudformation stack: %s" %
                      stack['StackName'])
                response = client.delete_stack(
                    StackName=stack['StackName'])
            except Exception as ex:
                print ex.message

def lambda_handler(event, context):
    volume_id = []
    global TemplateURL
    export = {}
    client = boto3.client('cloudformation')
    print (event)
    export = client.list_exports()
    for item in export['Exports']:
        if item['Name'] == 'CFUrl':
            TemplateURL = item['Value']
    print ("CF URL: %s" % TemplateURL)
    cloudtrail_event = get_cloudtrail_event(event)
    for log_event in cloudtrail_event['logEvents']:
        trail_message = get_message_from_cloudtrail_event(log_event)
        volume_id = trail_message['requestParameters']['resourcesSet']['items'][0]['resourceId']
        if trail_message['eventName'] == "CreateTags":
            for item in trail_message['requestParameters']['tagSet']['items']:
                if item['key'] == 'ChangeEBSType':
                    cf_parameter = item['value']
                    break
    if trail_message['eventName'] == "CreateTags":
        start_stop = cf_parameter.split(',')
        i = 0
        for schedule in start_stop:
            stack_name = "change-ebs-type-" + str(i) + "-" + volume_id
            build_ebs_volume_change_schedule(
                stack_name, schedule, volume_id, client)
            i = i + 1
    if trail_message['eventName'] == "DeleteTags":
        delete_ebs_volume_change_schedule(volume_id, client)

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特殊处理：由于中国区的 Lambda 尚不支持环境变量，修改 EBS 卷的 CloudFormation 模板 URL 无法传给 Python 程序，所以利用了 CloudFormation 的 Export 功能，通过将 URL 变成 Export 的变量，在 Python 里面读取这个变量完成参数传递。 CloudFormation： “Outputs”: { “CFPath”: { “Description”: “The URL of CF”, “Value”: { “Ref”: “CFUrl” }, “Export”: { “Name”: “CFUrl” } } }

对应的 Python 语句：

global TemplateURL
    export = {}
    client = boto3.client('cloudformation')
    export = client.list_exports()
    for item in export['Exports']:
        if item['Name'] == 'CFUrl':
            TemplateURL = item['Value']
    print ("CF URL: %s" % TemplateURL)

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EBS 卷的 Tag (ChangeEBSType)的格式有如下约定：

卷类型:IOPS 值:变更起始计划, 卷类型:IOPS 值:变更起始计划

例如如下设置：

io1:30000:(0 11 * * ? *),gp2:100:(0 19 * * ? *)

可以解释为：每天 11 点（UTC 时间）将当前的卷变更为 IOPS 为 30000 的 io1 类型，同日 19 点（UTC 时间）将当前卷恢复成 gp2 类型。（注意 gp2 类型的 EBS 卷忽略 IOPS 的值，所有 IOPS 值可以随意写，但不能为空值）

因为 EBS 卷的变更最小间隔时间为 6 小时，所以要确保 6 个小时内仅有一次磁盘类型的变更。

CloudWatch Event Rule可以通过如下CloudFormation的JSON语句创建：
"MyEventsRule": {
"Type": "AWS::Events::Rule",
"Properties": {
"Description": "Events Rule Invoke Lambda",
"Name": {
"Fn::Sub": "${AWS::StackName}-ChangeEBSEvent"
},
"ScheduleExpression": {
"Ref": "ScheduleExpression"
},
"State": "ENABLED",
"Targets": [{
"Arn": {
"Fn::GetAtt": [
"ModifyEbs",
"Arn"
]
},
"Id": "ModifyEbs"
}]
}
}