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Elastic Load Balancing
Network Load Balancers

CloudWatch Metrics for Your Network Load Balancer

Elastic Load Balancing publishes data points to Amazon CloudWatch for your load balancers and your targets. CloudWatch enables you to retrieve statistics about those data points as an ordered set of time-series data, known as metrics. Think of a metric as a variable to monitor, and the data points as the values of that variable over time. For example, you can monitor the total number of healthy targets for a load balancer over a specified time period. Each data point has an associated time stamp and an optional unit of measurement.

You can use metrics to verify that your system is performing as expected. For example, you can create a CloudWatch alarm to monitor a specified metric and initiate an action (such as sending a notification to an email address) if the metric goes outside what you consider an acceptable range.

Elastic Load Balancing reports metrics to CloudWatch only when requests are flowing through the load balancer. If there are requests flowing through the load balancer, Elastic Load Balancing measures and sends its metrics in 60-second intervals. If there are no requests flowing through the load balancer or no data for a metric, the metric is not reported.

For more information, see the Amazon CloudWatch User Guide.

Network Load Balancer Metrics

The AWS/NetworkELB namespace includes the following metrics.

Metric Description
ActiveFlowCount

The total number of concurrent TCP flows (or connections) from clients to targets. This metric includes only the connections in the ESTABLISHED state. TCP connections are not terminated at the load balancer, so a client opening a TCP connection to a target counts as a single flow.

Statistics: The most useful statistics are Average, Maximum, and Minimum.

ConsumedLCUs

The number of load balancer capacity units (LCU) used by your load balancer. You pay for the number of LCUs that you use per hour. For more information, see Elastic Load Balancing Pricing.

HealthyHostCount

The number of targets that are considered healthy.

Statistics: The most useful statistics are Average, Maximum, and Minimum.

NewFlowCount

The total number of new TCP flows (or connections) established from clients to targets in the time period.

Statistics: The most useful statistic is Sum.

ProcessedBytes

The total number of bytes processed by the load balancer, including TCP/IP headers.

Statistics: The most useful statistic is Sum.

TCP_Client_Reset_Count

The total number of reset (RST) packets sent from a client to a target. These resets are generated by the client and forwarded by the load balancer.

Statistics: The most useful statistic is Sum.

TCP_ELB_Reset_Count

The total number of reset (RST) packets generated by the load balancer.

Statistics: The most useful statistic is Sum.

TCP_Target_Reset_Count

The total number of reset (RST) packets sent from a target to a client. These resets are generated by the target and forwarded by the load balancer.

Statistics: The most useful statistic is Sum.

UnHealthyHostCount

The number of targets that are considered unhealthy.

Statistics: The most useful statistics are Average, Maximum, and Minimum.

Metric Dimensions for Network Load Balancers

To filter the metrics for your load balancer, use the following dimensions.

Dimension Description
AvailabilityZone

Filter the metric data by Availability Zone.

LoadBalancer

Filter the metric data by load balancer. Specify the load balancer as follows: net/load-balancer-name/1234567890123456 (the final portion of the load balancer ARN).

TargetGroup

Filter the metric data by target group. Specify the target group as follows: targetgroup/target-group-name/1234567890123456 (the final portion of the target group ARN).

Statistics for Network Load Balancer Metrics

CloudWatch provides statistics based on the metric data points published by Elastic Load Balancing. Statistics are metric data aggregations over specified period of time. When you request statistics, the returned data stream is identified by the metric name and dimension. A dimension is a name/value pair that uniquely identifies a metric. For example, you can request statistics for all the healthy EC2 instances behind a load balancer launched in a specific Availability Zone.

The Minimum and Maximum statistics reflect the minimum and maximum reported by the individual load balancer nodes. For example, suppose there are 2 load balancer nodes. One node has HealthyHostCount with a Minimum of 2, a Maximum of 10, and an Average of 6, while the other node has HealthyHostCount with a Minimum of 1, a Maximum of 5, and an Average of 3. Therefore, the load balancer has a Minimum of 1, a Maximum of 10, and an Average of about 4.

The Sum statistic is the aggregate value across all load balancer nodes. Because metrics include multiple reports per period, Sum is only applicable to metrics that are aggregated across all load balancer nodes.

The SampleCount statistic is the number of samples measured. Because metrics are gathered based on sampling intervals and events, this statistic is typically not useful. For example, with HealthyHostCount, SampleCount is based on the number of samples that each load balancer node reports, not the number of healthy hosts.

View CloudWatch Metrics for Your Load Balancer

You can view the CloudWatch metrics for your load balancers using the Amazon EC2 console. These metrics are displayed as monitoring graphs. The monitoring graphs show data points if the load balancer is active and receiving requests.

Alternatively, you can view metrics for your load balancer using the CloudWatch console.

To view metrics using the Amazon EC2 console

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. To view metrics filtered by target group, do the following:

    1. In the navigation pane, choose Target Groups.

    2. Select your target group and choose Monitoring.

    3. (Optional) To filter the results by time, select a time range from Showing data for.

    4. To get a larger view of a single metric, select its graph. The following metrics are available:

      • Healthy Hosts — HealthyHostCount

      • Unhealthy Hosts — UnHealthyHostCount

  3. To view metrics filtered by load balancer, do the following:

    1. In the navigation pane, choose Load Balancers.

    2. Select your load balancer and choose Monitoring.

    3. (Optional) To filter the results by time, select a time range from Showing data for.

    4. To get a larger view of a single metric, select its graph. The following metrics are available:

      • Active flow count — ActiveFlowCount

      • New flow count — NewFlowCount

      • Load balancer reset count — TCP_ELB_Reset_Count

      • Client reset count — TCP_Client_Reset_Count

      • Target reset count — TCP_Target_Reset_Count

      • Processed bytes — ProcessedBytes

To view metrics using the CloudWatch console

  1. Open the CloudWatch console at https://console.aws.amazon.com/cloudwatch/.

  2. In the navigation pane, choose Metrics.

  3. Select the NetworkELB namespace.

  4. (Optional) To view a metric across all dimensions, type its name in the search field.

To view metrics using the AWS CLI

Use the following list-metrics command to list the available metrics:

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aws cloudwatch list-metrics --namespace AWS/NetworkELB

To get the statistics for a metric using the AWS CLI

Use the following get-metric-statistics command get statistics for the specified metric and dimension. Note that CloudWatch treats each unique combination of dimensions as a separate metric. You can't retrieve statistics using combinations of dimensions that were not specially published. You must specify the same dimensions that were used when the metrics were created.

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aws cloudwatch get-metric-statistics --namespace AWS/NetworkELB \ --metric-name UnHealthyHostCount --statistics Average --period 3600 \ --dimensions Name=LoadBalancer,Value=net/my-load-balancer/50dc6c495c0c9188 \ Name=TargetGroup,Value=targetgroup/my-targets/73e2d6bc24d8a067 \ --start-time 2017-04-18T00:00:00Z --end-time 2017-04-21T00:00:00Z

The following is example output:

{
    "Datapoints": [
        {
            "Timestamp": "2017-04-18T22:00:00Z",
            "Average": 0.0,
            "Unit": "Count"
        },
        {
            "Timestamp": "2017-04-18T04:00:00Z",
            "Average": 0.0,
            "Unit": "Count"
        },
        ...
    ],
    "Label": "UnHealthyHostCount"
}