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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 timeseries 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 60second 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.
Contents
The AWS/ApplicationELB
namespace includes the following metrics for load balancers.
Metric  Description 

ActiveConnectionCount 
The total number of concurrent TCP connections active from clients to the load balancer and from the load balancer to targets. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

ClientTLSNegotiationErrorCount 
The number of TLS connections initiated by the client that did not establish a session with the load balancer due to a TLS error. Possible causes include a mismatch of ciphers or protocols or the client failing to verify the server certificate and closing the connection. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

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 Reporting criteria: Always reported Statistics: All Dimensions

DroppedInvalidHeaderRequestCount 
The number of requests where the load balancer removed HTTP headers with header
fields that are not valid before routing the request. The load balancer removes
these headers only if the Reporting criteria: Always reported Statistics: All Dimensions

ForwardedInvalidHeaderRequestCount 
The number of requests routed by the load balancer that had HTTP headers with
header fields that are not valid. The load balancer forwards requests with these
headers only if the Reporting criteria: Always reported Statistics: All Dimensions

HTTP_Fixed_Response_Count 
The number of fixedresponse actions that were successful. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

HTTP_Redirect_Count 
The number of redirect actions that were successful. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

HTTP_Redirect_Url_Limit_Exceeded_Count 
The number of redirect actions that couldn't be completed because the URL in the response location header is larger than 8K. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

HTTPCode_ELB_3XX_Count 
The number of HTTP 3XX redirection codes that originate from the load balancer. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

HTTPCode_ELB_4XX_Count 
The number of HTTP 4XX client error codes that originate from the load balancer. Client errors are generated when requests are malformed or incomplete. These requests were not received by the target, other than in the case where the load balancer returns an HTTP 460 error code. This count does not include any response codes generated by the targets. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

HTTPCode_ELB_5XX_Count 
The number of HTTP 5XX server error codes that originate from the load balancer. This count does not include any response codes generated by the targets. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

HTTPCode_ELB_500_Count 
The number of HTTP 500 error codes that originate from the load balancer. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

HTTPCode_ELB_502_Count 
The number of HTTP 502 error codes that originate from the load balancer. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

HTTPCode_ELB_503_Count 
The number of HTTP 503 error codes that originate from the load balancer. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

HTTPCode_ELB_504_Count 
The number of HTTP 504 error codes that originate from the load balancer. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

IPv6ProcessedBytes 
The total number of bytes processed by the load balancer over IPv6. This count is
included in
Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

IPv6RequestCount 
The number of IPv6 requests received by the load balancer. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

NewConnectionCount 
The total number of new TCP connections established from clients to the load balancer and from the load balancer to targets. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

ProcessedBytes 
The total number of bytes processed by the load balancer over IPv4 and IPv6. This count includes traffic to and from clients and Lambda functions, and traffic from an Identity Provider (IdP) if user authentication is enabled. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

RejectedConnectionCount 
The number of connections that were rejected because the load balancer had reached its maximum number of connections. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

RequestCount 
The number of requests processed over IPv4 and IPv6. This count includes only the requests with a response generated by a target of the load balancer. Reporting criteria: Always reported Statistics: The most useful statistic is Dimensions

RuleEvaluations 
The number of rules processed by the load balancer given a request rate averaged over an hour. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

The AWS/ApplicationELB
namespace includes the following metrics for targets.
Metric  Description 

HealthyHostCount 
The number of targets that are considered healthy. Reporting criteria: Reported if health checks are enabled Statistics: The most useful statistics are Dimensions

HTTPCode_Target_2XX_Count ,
HTTPCode_Target_3XX_Count ,
HTTPCode_Target_4XX_Count ,
HTTPCode_Target_5XX_Count 
The number of HTTP response codes generated by the targets. This does not include any response codes generated by the load balancer. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

NonStickyRequestCount 
The number of requests where the load balancer chose a new target because it couldn't use an existing sticky session. For example, the request was the first request from a new client and no stickiness cookie was presented, a stickiness cookie was presented but it did not specify a target that was registered with this target group, the stickiness cookie was malformed or expired, or an internal error prevented the load balancer from reading the stickiness cookie. Reporting criteria: Stickiness is enabled on the target group. Statistics: The only meaningful statistic is Dimensions

RequestCountPerTarget 
The average number of requests received by each target in a target group. You must
specify the target group
using the Reporting criteria: Always reported Statistics: The only valid statistic is Dimensions

TargetConnectionErrorCount 
The number of connections that were not successfully established between the load balancer and target. This metric does not apply if the target is a Lambda function. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

TargetResponseTime 
The time elapsed, in seconds, after the request leaves the load balancer
until a response from the target is received. This is equivalent to the
Reporting criteria: There is a nonzero value Statistics: The most useful statistics are Dimensions

TargetTLSNegotiationErrorCount 
The number of TLS connections initiated by the load balancer that did not establish a session with the target. Possible causes include a mismatch of ciphers or protocols. This metric does not apply if the target is a Lambda function. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

UnHealthyHostCount 
The number of targets that are considered unhealthy. Reporting criteria: Reported if health checks are enabled Statistics: The most useful statistics are Dimensions

The AWS/ApplicationELB
namespace includes the following metrics for Lambda functions
that are registered as targets.
Metric  Description 

LambdaInternalError 
The number of requests to a Lambda function that failed because of an issue internal to the load balancer or AWS Lambda. To get the error reason codes, check the error_reason field of the access log. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

LambdaTargetProcessedBytes 
The total number of bytes processed by the load balancer for requests to and responses from a Lambda function. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

LambdaUserError 
The number of requests to a Lambda function that failed because of an issue with the Lambda function. For example, the load balancer did not have permission to invoke the function, the load balancer received JSON from the function that is malformed or missing required fields, or the size of the request body or response exceeded the maximum size of 1 MB. To get the error reason codes, check the error_reason field of the access log. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

The AWS/ApplicationELB
namespace includes the following metrics for user authentication.
Metric  Description 

ELBAuthError 
The number of user authentications that could not be completed because an authenticate action was misconfigured, the load balancer couldn't establish a connection with the IdP, or the load balancer couldn't complete the authentication flow due to an internal error. To get the error reason codes, check the error_reason field of the access log. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

ELBAuthFailure 
The number of user authentications that could not be completed because the IdP denied access to the user or an authorization code was used more than once. To get the error reason codes, check the error_reason field of the access log. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

ELBAuthLatency 
The time elapsed, in milliseconds, to query the IdP for the ID token and user info. If one or more of these operations fail, this is the time to failure. Reporting criteria: There is a nonzero value Statistics: All statistics are meaningful. Dimensions

ELBAuthRefreshTokenSuccess 
The number of times the load balancer successfully refreshed user claims using a refresh token provided by the IdP. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

ELBAuthSuccess 
The number of authenticate actions that were successful. This metric is incremented at the end of the authentication workflow, after the load balancer has retrieved the user claims from the IdP. Reporting criteria: There is a nonzero value Statistics: The most useful statistic is Dimensions

ELBAuthUserClaimsSizeExceeded 
The number of times that a configured IdP returned user claims that exceeded 11K bytes in size. Reporting criteria: There is a nonzero value Statistics: The only meaningful statistic is Dimensions

To filter the metrics for your Application Load Balancer, use the following dimensions.
Dimension  Description 

AvailabilityZone 
Filters the metric data by Availability Zone. 
LoadBalancer 
Filters the metric data by load balancer. Specify the load balancer as follows: app/loadbalancername/1234567890123456 (the final portion of the load balancer ARN). 
TargetGroup 
Filters the metric data by target group. Specify the target group as follows: targetgroup/targetgroupname/1234567890123456 (the final portion of the target group ARN). 
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 namevalue 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.
A percentile indicates the relative standing of a value in a data set. You can specify any percentile, using up to two decimal places (for example, p95.45). For example, the 95th percentile means that 95 percent of the data is below this value and 5 percent is above. Percentiles are often used to isolate anomalies. For example, suppose that an application serves the majority of requests from a cache in 12 ms, but in 100200 ms if the cache is empty. The maximum reflects the slowest case, around 200 ms. The average doesn't indicate the distribution of the data. Percentiles provide a more meaningful view of the application's performance. By using the 99th percentile as an Auto Scaling trigger or a CloudWatch alarm, you can target that no more than 1 percent of requests take longer than 2 ms to process.
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
Open the Amazon EC2 console at
https://console.aws.amazon.com/ec2/
To view metrics filtered by target group, do the following:
In the navigation pane, choose Target Groups.
Select your target group, and then choose the Monitoring tab.
(Optional) To filter the results by time, select a time range from Showing data for.
To get a larger view of a single metric, select its graph.
To view metrics filtered by load balancer, do the following:
In the navigation pane, choose Load Balancers.
Select your load balancer, and then choose the Monitoring tab.
(Optional) To filter the results by time, select a time range from Showing data for.
To get a larger view of a single metric, select its graph.
To view metrics using the CloudWatch console
Open the CloudWatch console at
https://console.aws.amazon.com/cloudwatch/
In the navigation pane, choose Metrics.
Select the ApplicationELB namespace.
(Optional) To view a metric across all dimensions, type its name in the search field.
(Optional) To filter by dimension, select one of the following:
To display only the metrics reported for your load balancers, choose Per AppELB Metrics. To view the metrics for a single load balancer, type its name in the search field.
To display only the metrics reported for your target groups, choose Per AppELB, per TG Metrics. To view the metrics for a single target group, type its name in the search field.
To display only the metrics reported for your load balancers by Availability Zone, choose Per AppELB, per AZ Metrics. To view the metrics for a single load balancer, type its name in the search field. To view the metrics for a single Availability Zone, type its name in the search field.
To display only the metrics reported for your load balancers by Availability Zone and target group, choose Per AppELB, per AZ, per TG Metrics. To view the metrics for a single load balancer, type its name in the search field. To view the metrics for a single target group, type its name in the search field. To view the metrics for a single Availability Zone, type its name in the search field.
To view metrics using the AWS CLI
Use the following listmetrics command to list the available metrics:
aws cloudwatch listmetrics namespace AWS/ApplicationELB
To get the statistics for a metric using the AWS CLI
Use the following getmetricstatistics 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.
aws cloudwatch getmetricstatistics namespace AWS/ApplicationELB \ metricname UnHealthyHostCount statistics Average period 3600 \ dimensions Name=LoadBalancer,Value=app/myloadbalancer/50dc6c495c0c9188 \ Name=TargetGroup,Value=targetgroup/mytargets/73e2d6bc24d8a067 \ starttime 20160418T00:00:00Z endtime 20160421T00:00:00Z
The following is example output:
{
"Datapoints": [
{
"Timestamp": "20160418T22:00:00Z",
"Average": 0.0,
"Unit": "Count"
},
{
"Timestamp": "20160418T04:00:00Z",
"Average": 0.0,
"Unit": "Count"
},
...
],
"Label": "UnHealthyHostCount"
}