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ELB CloudWatch Metrics

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In this, we will understand the concepts of ELB CloudWatch Metrics.

SOA-C01 exam is updated to AWS Certified SysOps Administrator – Associate (SOA-C02).

Classic Load Balancer Metrics

The AWS/ELB namespace includes the following metrics.

MetricDescription
BackendConnectionErrorsThe number of connections that were not successfully established between the load balancer and the registered instances.
HealthyHostCountThe number of healthy instances registered with your load balancer. A newly registered instance is considered healthy after it passes the first health check. If cross-zone load balancing is enabled, the number of healthy instances for the LoadBalancerName dimension is calculated across all Availability Zones. Otherwise, it is calculated per Availability Zone.
HTTPCode_Backend_2XX, HTTPCode_Backend_3XX, HTTPCode_Backend_4XX, HTTPCode_Backend_5XX [HTTP listener] The number of HTTP response codes generated by registered instances. This count does not include any response codes generated by the load balancer.
HTTPCode_ELB_4XX[HTTP listener] The number of HTTP 4XX client error codes generated by the load balancer. Client errors are generated when a request is malformed or incomplete. 
HTTPCode_ELB_5XX [HTTP listener] The number of HTTP 5XX server error codes generated by the load balancer. This count does not include any response codes generated by the registered instances. The metric is reported if there are no healthy instances registered to the load balancer, or if the request rate exceeds the capacity of the instances (spillover) or the load balancer.
Latency[HTTP listener] The total time elapsed, in seconds, from the time the load balancer sent the request to a registered instance until the instance started to send the response headers. [TCP listener] The total time elapsed, in seconds, for the load balancer to successfully establish a connection to a registered instance.
RequestCount The number of requests completed or connections made during the specified interval (1 or 5 minutes).
SpilloverCount The total number of requests that were rejected because the surge queue is full. [HTTP listener] The load balancer returns an HTTP 503 error code. [TCP listener] The load balancer closes the connection.
SurgeQueueLength The total number of requests (HTTP listener) or connections (TCP listener) that are pending routing to a healthy instance. The maximum size of the queue is 1,024. Additional requests or connections are rejected when the queue is full. For more information, see SpilloverCount. 
UnHealthyHostCount The number of unhealthy instances registered with your load balancer. An instance is considered unhealthy after it exceeds the unhealthy threshold configured for health checks. An unhealthy instance is considered healthy again after it meets the healthy threshold configured for health checks.

Application Load Balancer Metrics

The AWS/ApplicationELB namespace includes the following metrics for load balancers.

MetricDescription
ActiveConnectionCount The total number of concurrent TCP connections active from clients to the load balancer and from the load balancer to targets.
ClientTLSNegotiationErrorCount The number of TLS connections initiated by the client that did not establish a session with the load balancer. Possible causes include a mismatch of ciphers or protocols.
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.
HTTP_Fixed_Response_Count The number of fixed-response actions that were successful.
HTTP_Redirect_Count The number of redirect actions that were successful.
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.
HTTPCode_ELB_3XX_Count The number of HTTP 3XX redirection codes that originate from the load balancer.
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 have not been received by the target.
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.
HTTPCode_ELB_500_Count The number of HTTP 500 error codes that originate from the load balancer.
HTTPCode_ELB_502_Count The number of HTTP 502 error codes that originate from the load balancer.
HTTPCode_ELB_503_Count The number of HTTP 503 error codes that originate from the load balancer.
HTTPCode_ELB_504_Count The number of HTTP 504 error codes that originate from the load balancer.
IPv6ProcessedBytes The total number of bytes processed by the load balancer over IPv6.
IPv6RequestCount The number of IPv6 requests received by the load balancer.
NewConnectionCount The total number of new TCP connections established from clients to the load balancer and from the load balancer to targets.
ProcessedBytes The total number of bytes processed by the load balancer over IPv4 and IPv6.
RejectedConnectionCount The number of connections that were rejected because the load balancer had reached its maximum number of connections.
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.
RuleEvaluations The number of rules processed by the load balancer given a request rate averaged over an hour.
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