CloudWatch Metric Guide
Application Load Balancer CloudWatch AlarmsThresholds, failures, and debugging guides
3 CloudWatch metrics covered for Application Load Balancer. Each guide includes the recommended alarm threshold, common root causes, and how Nuberio automatically diagnoses it when it fires.
3
metrics covered
AWS/ApplicationELB
namespace
5 min
to run a free audit
Application Load Balancer metrics
HTTPCode_ELB_5XX_Count
HTTPCode_ELB_5XX_Count counts HTTP 5XX response codes generated by the load balancer itself — not by the registered targets. These indicate the ALB could not deliver the request to a healthy target.
Threshold
> 0 in any 5-minute window
TargetResponseTime
TargetResponseTime measures the time elapsed from when the ALB sent the request to a registered target until the target started sending a response, in seconds. CloudWatch exposes this as p50, p90, p95, and p99 percentiles.
Threshold
p99 TargetResponseTime > your defined SLA threshold (typically 1s for APIs, 3s for pages)
UnHealthyHostCount
UnHealthyHostCount reports the number of targets (EC2 instances, ECS tasks, Lambda functions) registered with the ALB target group that are currently failing health checks.
Threshold
> 0 (any unhealthy host in a production target group)
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Looking for alarms across other AWS services? View the full CloudWatch metric guide — thresholds and debugging guides for RDS, Lambda, ECS, ALB, EC2, DynamoDB, SQS, API Gateway, S3, CloudFront, ElastiCache, and EKS.