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| Data path availability (VIP availability)| Public and internal load balancer | Standard Load Balancer continuously exercises the data path from within a region to the load balancer front end, all the way to the SDN stack that supports your VM. As long as healthy instances remain, the measurement follows the same path as your application's load-balanced traffic. The data path that your customers use is also validated. The measurement is invisible to your application and does not interfere with other operations.| Average |
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| Health probe status(DIP availability) | Public and internal load balancer | Standard Load Balancer uses a distributed health-probing service that monitors your application endpoint's health according to your configuration settings. This metric provides an aggregate or per-endpoint filtered view of each instance endpoint in the load balancer pool. You can see how Load Balancer views the health of your application, as indicated by your health probe configuration. | Average |
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| Data path availability (Frontend availability)| Public and internal load balancer | Standard Load Balancer continuously exercises the data path from within a region to the load balancer front end, all the way to the SDN stack that supports your VM. As long as healthy instances remain, the measurement follows the same path as your application's load-balanced traffic. The data path that your customers use is also validated. The measurement is invisible to your application and does not interfere with other operations.| Average |
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| Health probe status(Backend Instance availability) | Public and internal load balancer | Standard Load Balancer uses a distributed health-probing service that monitors your application endpoint's health according to your configuration settings. This metric provides an aggregate or per-endpoint filtered view of each instance endpoint in the load balancer pool. You can see how Load Balancer views the health of your application, as indicated by your health probe configuration. | Average |
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| SYN (synchronize) packets | Public and internal load balancer | Standard Load Balancer does not terminate Transmission Control Protocol (TCP) connections or interact with TCP or UDP packet flows. Flows and their handshakes are always between the source and the VM instance. To better troubleshoot your TCP protocol scenarios, you can make use of SYN packets counters to understand how many TCP connection attempts are made. The metric reports the number of TCP SYN packets that were received.| Average |
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| SNAT connections | Public load balancer |Standard Load Balancer reports the number of outbound flows that are masqueraded to the Public IP address front end. Source network address translation (SNAT) ports are an exhaustible resource. This metric can give an indication of how heavily your application is relying on SNAT for outbound originated flows. Counters for successful and failed outbound SNAT flows are reported and can be used to troubleshoot and understand the health of your outbound flows.| Average |
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| Allocated SNAT ports | Public load balancer | Standard Load Balancer reports the number of SNAT ports allocated per backend instance | Average. |
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### <aname = "DiagnosticScenarios"></a>Common diagnostic scenarios and recommended views
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#### Is the data path up and available for my load balancer VIP?
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#### Is the data path up and available for my Load Balancer Frontend?
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<details><summary>Expand</summary>
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The VIP availability metric describes the health of the data path within the region to the compute host where your VMs are located. The metric is a reflection of the health of the Azure infrastructure. You can use the metric to:
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The data path availability availability metric describes the health of the data path within the region to the compute host where your VMs are located. The metric is a reflection of the health of the Azure infrastructure. You can use the metric to:
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- Monitor the external availability of your service
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- Dig deeper and understand whether the platform on which your service is deployed is healthy or whether your guest OS or application instance is healthy.
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- Isolate whether an event is related to your service or the underlying data plane. Do not confuse this metric with the health probe status ("DIP availability").
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- Isolate whether an event is related to your service or the underlying data plane. Do not confuse this metric with the health probe status ("Backend Instance availability").
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To get the Data Path Availability for your Standard Load Balancer resources:
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1. Make sure the correct load balancer resource is selected.
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A packet matching your deployment's front end and rule is generated periodically. It traverses the region from the source to the host where a VM in the back-end pool is located. The load balancer infrastructure performs the same load balancing and translation operations as it does for all other traffic. This probe is in-band on your load-balanced endpoint. After the probe arrives on the compute host, where a healthy VM in the back-end pool is located, the compute host generates a response to the probing service. Your VM does not see this traffic.
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VIP availability fails for the following reasons:
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Datapath availability availability fails for the following reasons:
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- Your deployment has no healthy VMs remaining in the back-end pool.
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- An infrastructure outage has occurred.
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@@ -111,7 +111,7 @@ For diagnostic purposes, you can use the [Data Path Availability metric together
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Use **Average** as the aggregation for most scenarios.
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</details>
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#### Are the back-end instances for my VIP responding to probes?
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#### Are the Backend Instances for my Load Balancer responding to probes?
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<details>
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<summary>Expand</summary>
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The health probe status metric describes the health of your application deployment as configured by you when you configure the health probe of your load balancer. The load balancer uses the status of the health probe to determine where to send new flows. Health probes originate from an Azure infrastructure address and are visible within the guest OS of the VM.
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#### <aname = "vipavailabilityandhealthprobes"></a>How do I diagnose my load balancer deployment?
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<details>
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<summary>Expand</summary>
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By using a combination of the VIP availability and health probe metrics on a single chart you can identify where to look for the problem and resolve the problem. You can gain assurance that Azure is working correctly and use this knowledge to conclusively determine that the configuration or application is the root cause.
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By using a combination of the Data Path Availability and Health Probe Status metrics on a single chart you can identify where to look for the problem and resolve the problem. You can gain assurance that Azure is working correctly and use this knowledge to conclusively determine that the configuration or application is the root cause.
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You can use health probe metrics to understand how Azure views the health of your deployment as per the configuration you have provided. Looking at health probes is always a great first step in monitoring or determining a cause.
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You can take it a step further and use VIP availability metrics to gain insight into how Azure views the health of the underlying data plane that's responsible for your specific deployment. When you combine both metrics, you can isolate where the fault might be, as illustrated in this example:
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You can take it a step further and use Data Path availability metric to gain insight into how Azure views the health of the underlying data plane that's responsible for your specific deployment. When you combine both metrics, you can isolate where the fault might be, as illustrated in this example:
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*Figure: Combining Data Path Availability and Health Probe Status metrics*
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The chart displays the following information:
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- The infrastructure hosting your VMs was unavailable and at 0 percent at the beginning of the chart. Later, the infrastructure was healthy and the VMs were reachable, and more than one VM was placed in the back end. This information is indicated by the blue trace for data path availability (VIP availability), which was later at 100 percent.
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- The health probe status (DIP availability), indicated by the purple trace, is at 0 percent at the beginning of the chart. The circled area in green highlights where the health probe status (DIP availability) became healthy, and at which point the customer's deployment was able to accept new flows.
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- The infrastructure hosting your VMs was unavailable and at 0 percent at the beginning of the chart. Later, the infrastructure was healthy and the VMs were reachable, and more than one VM was placed in the back end. This information is indicated by the blue trace for data path availability, which was later at 100 percent.
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- The health probe status, indicated by the purple trace, is at 0 percent at the beginning of the chart. The circled area in green highlights where the health probe status became healthy, and at which point the customer's deployment was able to accept new flows.
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The chart allows customers to troubleshoot the deployment on their own without having to guess or ask support whether other issues are occurring. The service was unavailable because health probes were failing due to either a misconfiguration or a failed application.
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