面试题：C# 云原生应用中利用 AWS/Azure SDK 进行负载均衡与容错处理

使用 AWS Elastic Load Balancing SDK

配置负载均衡策略：
- 选择负载均衡器类型：AWS 有多种负载均衡器，如 Application Load Balancer（ALB）用于 HTTP/HTTPS 流量，Network Load Balancer（NLB）用于 TCP/UDP 流量。根据应用类型选择合适的负载均衡器。例如，对于 Web 应用，通常选择 ALB。
- 设置监听器：监听器用于监听传入的流量并将其路由到目标组。可以使用以下代码示例设置监听器：

var elbClient = new AmazonElasticLoadBalancingClient();
var createListenerRequest = new CreateListenerRequest
{
    LoadBalancerArn = loadBalancerArn,
    Protocol = Protocol.Http,
    Port = 80,
    DefaultActions = new List<Action>
    {
        new Action
        {
            Type = ActionType.Forward,
            TargetGroupArn = targetGroupArn
        }
    }
};
var createListenerResponse = await elbClient.CreateListenerAsync(createListenerRequest);

配置目标组：目标组包含后端服务实例。可以设置健康检查，以确保只有健康的实例接收流量。例如：

var createTargetGroupRequest = new CreateTargetGroupRequest
{
    Name = "my - target - group",
    Protocol = Protocol.Http,
    Port = 80,
    VpcId = vpcId,
    HealthCheckPath = "/healthcheck",
    HealthCheckProtocol = Protocol.Http,
    HealthCheckIntervalSeconds = 30,
    HealthCheckTimeoutSeconds = 5,
    HealthyThresholdCount = 3,
    UnhealthyThresholdCount = 5
};
var createTargetGroupResponse = await elbClient.CreateTargetGroupAsync(createTargetGroupRequest);

容错处理：
- 健康检查：AWS ELB 会自动对目标组中的实例进行健康检查。当实例不健康时，ELB 会停止向其发送流量。
- 自动替换不健康实例：如果启用了自动扩展组（Auto Scaling Group），当某个实例不健康时，自动扩展组可以启动新的实例来替换它。代码示例：

var asgClient = new AmazonAutoScalingClient();
var describeAutoScalingGroupsRequest = new DescribeAutoScalingGroupsRequest
{
    AutoScalingGroupNames = new List<string> { "my - asg - name" }
};
var describeAutoScalingGroupsResponse = await asgClient.DescribeAutoScalingGroupsAsync(describeAutoScalingGroupsRequest);
var asg = describeAutoScalingGroupsResponse.AutoScalingGroups.FirstOrDefault();
if (asg!= null)
{
    var instance = asg.Instances.FirstOrDefault(i => i.HealthStatus!= "Healthy");
    if (instance!= null)
    {
        var terminateInstanceInAutoScalingGroupRequest = new TerminateInstanceInAutoScalingGroupRequest
        {
            InstanceId = instance.InstanceId,
            ShouldDecrementDesiredCapacity = true
        };
        await asgClient.TerminateInstanceInAutoScalingGroupAsync(terminateInstanceInAutoScalingGroupRequest);
    }
}

使用 Azure Load Balancer SDK

配置负载均衡策略：
- 创建负载均衡器：可以使用 Azure SDK for.NET 创建负载均衡器。例如：

var azure = Azure.Authenticate(credentials).WithSubscription(subscriptionId);
var loadBalancer = await azure.Network.LoadBalancers.Define("myLoadBalancer")
   .WithRegion(Region.USWest)
   .WithExistingResourceGroup(resourceGroupName)
   .CreateAsync();

配置前端 IP 配置：定义负载均衡器接收流量的 IP 地址。

var frontendIPConfiguration = await loadBalancer.Update()
   .DefineFrontendIP("myFrontendIP")
   .WithExistingSubnet(subnet)
   .WithPublicIPAddress(publicIPAddress)
   .AttachAsync();

配置后端地址池：后端地址池包含后端服务实例。

var backendAddressPool = await loadBalancer.Update()
   .DefineBackendAddressPool("myBackendAddressPool")
   .AttachAsync();

配置健康探测：设置健康探测以检查后端实例的健康状况。

var probe = await loadBalancer.Update()
   .DefineProbe("myProbe")
   .ForTcp()
   .OnPort(80)
   .WithIntervalInSeconds(15)
   .WithNumberOfProbes(2)
   .AttachAsync();

配置负载均衡规则：将前端 IP 配置、后端地址池和健康探测关联起来。

await loadBalancer.Update()
   .DefineLoadBalancingRule("myLoadBalancingRule")
   .FromFrontendIPConfiguration(frontendIPConfiguration)
   .WithProtocol(Tcp)
   .FromPort(80)
   .ToPort(80)
   .ForwardToBackendAddressPool(backendAddressPool)
   .WithProbe(probe)
   .AttachAsync();

容错处理：
- 健康探测：Azure Load Balancer uses the configured health probe to detect unhealthy instances. When an instance fails the health probe, the load balancer stops sending traffic to it.
- 自动修复：Azure Availability Sets or Virtual Machine Scale Sets can be used to automatically replace unhealthy instances. For example, with a Virtual Machine Scale Set:

var scaleSet = await azure.Compute.VirtualMachineScaleSets.GetByResourceGroupAsync(resourceGroupName, "myScaleSet");
var instances = await scaleSet.GetVMsAsync();
foreach (var instance in instances)
{
    var instanceView = await instance.InstanceViewAsync();
    if (instanceView.Statuses.Any(s => s.Code.Contains("ProvisioningState/failed") || s.Code.Contains("PowerState/off")))
    {
        await scaleSet.DeleteInstanceAsync(instance.Index);
    }
}

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面试题：C# 云原生应用中利用 AWS/Azure SDK 进行负载均衡与容错处理

知识考点

面试题答案

使用 AWS Elastic Load Balancing SDK

使用 Azure Load Balancer SDK