AWS 的解决方案：

• 弹性负载均衡器（ELB），用于同步解耦。
  • Application Load Balancer；
  • 网络负载均衡器；
  • Classic Load Balancer；
• 消息队列服务（SQS），用于异步解耦。

一、利用负载均衡器实现同步解耦

实现将流量与 Web 服务器解耦。

负载均衡器同步解耦服务器

• 负载均衡器将传入的请求路由到两个后端的Web服务器之一；
• 负载均衡器可以通过 DNS 从互联网访问；
• Web 服务器只能通过负载均衡器访问；

CloudFormation 示例模版代码：

{
    "AWSTemplateFormatVersion": "2010-09-09",
    "Description": "AWS in Action: chapter 12 (Load Balancer)",
    "Parameters": {
        "KeyName": {
            "Description": "Key Pair name",
            "Type": "AWS::EC2::KeyPair::KeyName",
            "Default": "mykey"
        },
        "NumberOfServers": {
            "Description": "Number of servers",
            "Type": "Number",
            "Default": "2",
            "MinValue": "2",
            "MaxValue": "4"
        }
    },
    "Mappings": {
        "EC2RegionMap": {
            "ap-northeast-1": {"AmazonLinuxAMIHVMEBSBacked64bit": "ami-cbf90ecb"},
            "ap-southeast-1": {"AmazonLinuxAMIHVMEBSBacked64bit": "ami-68d8e93a"},
            "ap-southeast-2": {"AmazonLinuxAMIHVMEBSBacked64bit": "ami-fd9cecc7"},
            "eu-central-1": {"AmazonLinuxAMIHVMEBSBacked64bit": "ami-a8221fb5"},
            "eu-west-1": {"AmazonLinuxAMIHVMEBSBacked64bit": "ami-a10897d6"},
            "sa-east-1": {"AmazonLinuxAMIHVMEBSBacked64bit": "ami-b52890a8"},
            "us-east-1": {"AmazonLinuxAMIHVMEBSBacked64bit": "ami-1ecae776"},
            "us-west-1": {"AmazonLinuxAMIHVMEBSBacked64bit": "ami-d114f295"},
            "us-west-2": {"AmazonLinuxAMIHVMEBSBacked64bit": "ami-e7527ed7"}
        }
    },
    "Resources": {
        "VPC": {
            "Type": "AWS::EC2::VPC",
            "Properties": {
                "CidrBlock": "172.31.0.0/16",
                "EnableDnsHostnames": "true"
            }
        },
        "InternetGateway": {
            "Type": "AWS::EC2::InternetGateway",
            "Properties": {
            }
        },
        "VPCGatewayAttachment": {
            "Type": "AWS::EC2::VPCGatewayAttachment",
            "Properties": {
                "VpcId": {"Ref": "VPC"},
                "InternetGatewayId": {"Ref": "InternetGateway"}
            }
        },
        "Subnet": {
            "Type": "AWS::EC2::Subnet",
            "Properties": {
                "AvailabilityZone": {"Fn::Select": ["0", {"Fn::GetAZs": ""}]},
                "CidrBlock": "172.31.38.0/24",
                "VpcId": {"Ref": "VPC"}
            }
        },
        "RouteTable": {
            "Type": "AWS::EC2::RouteTable",
            "Properties": {
                "VpcId": {"Ref": "VPC"}
            }
        },
        "RouteTableAssociation": {
            "Type": "AWS::EC2::SubnetRouteTableAssociation",
            "Properties": {
                "SubnetId": {"Ref": "Subnet"},
                "RouteTableId": {"Ref": "RouteTable"}
            }
        },
        "RoutePublicNATToInternet": {
            "Type": "AWS::EC2::Route",
            "Properties": {
                "RouteTableId": {"Ref": "RouteTable"},
                "DestinationCidrBlock": "0.0.0.0/0",
                "GatewayId": {"Ref": "InternetGateway"}
            },
            "DependsOn": "VPCGatewayAttachment"
        },
        "NetworkAcl": {
            "Type": "AWS::EC2::NetworkAcl",
            "Properties": {
                "VpcId": {"Ref": "VPC"}
            }
        },
        "SubnetNetworkAclAssociation": {
            "Type": "AWS::EC2::SubnetNetworkAclAssociation",
            "Properties": {
                "SubnetId": {"Ref": "Subnet"},
                "NetworkAclId": {"Ref": "NetworkAcl"}
            }
        },
        "NetworkAclEntryIngress": {
            "Type": "AWS::EC2::NetworkAclEntry",
            "Properties": {
                "NetworkAclId": {"Ref": "NetworkAcl"},
                "RuleNumber": "100",
                "Protocol": "-1",
                "RuleAction": "allow",
                "Egress": "false",
                "CidrBlock": "0.0.0.0/0"
            }
        },
        "NetworkAclEntryEgress": {
            "Type": "AWS::EC2::NetworkAclEntry",
            "Properties": {
                "NetworkAclId": {"Ref": "NetworkAcl"},
                "RuleNumber": "100",
                "Protocol": "-1",
                "RuleAction": "allow",
                "Egress": "true",
                "CidrBlock": "0.0.0.0/0"
            }
        },
        "LoadBalancerSecurityGroup": { # 负载均衡器安全组设置
            "Type": "AWS::EC2::SecurityGroup",
            "Properties": {
                "GroupDescription": "elb-sg",
                "VpcId": {"Ref": "VPC"},
                "SecurityGroupIngress": [{
                    "CidrIp": "0.0.0.0/0",
                    "FromPort": 80, # 负载均衡器只接受 80 端口的流量
                    "IpProtocol": "tcp",
                    "ToPort": 80
                }]
            }
        },
        "LoadBalancer": {
            "Type": "AWS::ElasticLoadBalancing::LoadBalancer",
            "Properties": {
                "Subnets": [{"Ref": "Subnet"}], # 将 ELB 附加到子网上
                "LoadBalancerName": "elb",
                "Listeners": [{ # 映射负载均衡器的端口到其后端的服务器端口
                    "InstancePort": "80",
                    "InstanceProtocol": "HTTP",
                    "LoadBalancerPort": "80",
                    "Protocol": "HTTP"
                }],
                "HealthCheck": { # ELB 健康状态检查
                    "Target": "HTTP:80/index.html", # 检查对/index.html 返回的状态码是否为 200
                    "Interval": "10", # 每 10s 进行一次检查
                    "Timeout": "5", # 超时时间为 5s
                    "UnhealthyThreshold": "2", # 检查连续失败2次，则认为是运行状况不好的
                    "HealthyThreshold": "3", # 检查连续通过 3 次才能认为是运行状况良好的
                },
                "SecurityGroups": [{"Ref": "LoadBalancerSecurityGroup"}], # 关联安全组
                "Scheme": "internet-facing" # 设置为公开可访问
            },
            "DependsOn": "VPCGatewayAttachment"
        },
        "WebServerSecurityGroup": {
            "Type": "AWS::EC2::SecurityGroup",
            "Properties": {
                "GroupDescription": "awsinaction-sg",
                "VpcId": {"Ref": "VPC"},
                "SecurityGroupIngress": [{
                    "CidrIp": "0.0.0.0/0",
                    "FromPort": 22,
                    "IpProtocol": "tcp",
                    "ToPort": 22
                }, {
                    "FromPort": 80,
                    "IpProtocol": "tcp",
                    "SourceSecurityGroupId": {"Ref": "LoadBalancerSecurityGroup"},
                    "ToPort": 80
                }]
            }
        },
        "LaunchConfiguration": {
            "Type": "AWS::AutoScaling::LaunchConfiguration",
            "Metadata": {
                "AWS::CloudFormation::Init": {
                    "config": {
                        "packages": {
                            "yum": {
                                "httpd": []
                            }
                        },
                        "files": {
                            "/tmp/config": {
                                "content": {"Fn::Join": ["", [
                                    "#!/bin/bash -ex\n",
                                    "PRIVATE_IP=`curl -s http://169.254.169.254/latest/meta-data/local-ipv4`\n",
                                    "echo \"<html><head><title>$PRIVATE_IP</title></head><body><h1>$PRIVATE_IP</h1></body></html>\" > index.html\n"
                                ]]},
                                "mode": "000500",
                                "owner": "root",
                                "group": "root"
                            }
                        },
                        "commands": {
                            "01_config": {
                                "command": "/tmp/config",
                                "cwd": "/var/www/html"
                            }
                        },
                        "services": {
                            "sysvinit": {
                                "httpd": {
                                    "enabled": "true",
                                    "ensureRunning": "true"
                                }
                            }
                        }
                    }
                }
            },
            "Properties": {
                "EbsOptimized": false,
                "ImageId": {"Fn::FindInMap": ["EC2RegionMap", {"Ref": "AWS::Region"}, "AmazonLinuxAMIHVMEBSBacked64bit"]},
                "InstanceType": "t2.micro",
                "SecurityGroups": [{"Ref": "WebServerSecurityGroup"}],
                "KeyName": {"Ref": "KeyName"},
                "AssociatePublicIpAddress": true,
                "UserData": {"Fn::Base64": {"Fn::Join": ["", [
                    "#!/bin/bash -ex\n",
                    "yum update -y aws-cfn-bootstrap\n",
                    "/opt/aws/bin/cfn-init -v --stack ", {"Ref": "AWS::StackName"}, " --resource LaunchConfiguration --region ", {"Ref": "AWS::Region"}, "\n",
                    "/opt/aws/bin/cfn-signal -e $? --stack ", {"Ref": "AWS::StackName"}, " --resource AutoScalingGroup --region ", {"Ref": "AWS::Region"}, "\n"
                ]]}}
            }
        },
        "AutoScalingGroup": { # 自动扩展
            "Type": "AWS::AutoScaling::AutoScalingGroup",
            "Properties": {
                "LoadBalancerNames": [{"Ref": "LoadBalancer"}], # 将自动扩展组连接到 ELB
                "LaunchConfigurationName": {"Ref": "LaunchConfiguration"},
                "MinSize": {"Ref": "NumberOfServers"}, # 最小尺寸
                "MaxSize": {"Ref": "NumberOfServers"}, # 最大尺寸
                "DesiredCapacity": {"Ref": "NumberOfServers"}, # 容量
                "VPCZoneIdentifier": [{"Ref": "Subnet"}]
            },
            "CreationPolicy": {
                "ResourceSignal": {
                    "Timeout": "PT10M"
                }
            },
            "DependsOn": "VPCGatewayAttachment"
        }
    },
    "Outputs": {
        "URL": {
            "Value": {"Fn::Join": ["", ["http://", {"Fn::GetAtt": ["LoadBalancer", "DNSName"]}]]},
            "Description": "Load Balancer URL"
        }
    }
}

更多使用场景

• 处理 TCP 流量；
• ELB 支持 SSL 证书。
• 记录日志，并将日志存储到 S3 上。
• 跨可用区的负载均衡。（建议启用跨可用区负载均衡，默认情况下是禁用的）。

二、利用消息队列实现异步解耦

Amazon Simple Queue Service

适用于微服务、分布式系统和无服务器应用程序的完全托管的消息队列

Amazon Simple Queue Service (SQS) 是一种完全托管的消息队列服务，可让您分离和扩展微服务、分布式系统和无服务器应用程序。SQS 消除了与管理和运营消息型中间件相关的复杂性和开销，并使开发人员能够专注于重要工作。借助 SQS，您可以在软件组件之间发送、存储和接收任何规模的消息，而不会丢失消息，并且无需其他服务即可保持可用。使用 AWS 控制台、命令行界面或您选择的 SDK 和三个简单的命令，在几分钟内即可开始使用 SQS。

SQS 提供两种消息队列类型。标准队列提供最高吞吐量、最大努力排序和至少一次传送。SQS FIFO 队列旨在确保按照消息的发送顺序对消息进行严格一次处理。