DDOT: ecs_cluster_name holds the cluster ARN, disagreeing with the Agent's ECS Fargate check

[tetienne]

Agent Environment

Datadog Agent 7.82.2 (public.ecr.aws/datadog/agent:7.82.2-full), DDOT collector v0.155.0, running as a sidecar in an ECS Fargate task (eu-west-1, Datadog EU site).

Describe what happened

Telemetry exported through DDOT gets ecs_cluster_name set to the full ECS cluster ARN, while the Agent's own ECS Fargate check reports the bare cluster name for the same tasks. Both land in the same org, under the same tag key.

OTLP spans from the sidecar:

ecs_cluster_name:arn:aws:ecs:eu-west-1:<account>:cluster/my-cluster

ecs.fargate.* metrics from the Agent, same tasks, same cluster:

ecs_cluster_name:my-cluster

Any dashboard, monitor or grouping on ecs_cluster_name splits into two values for one cluster.

The cause looks like a mapping that copies the value unchanged:

https://github.com/DataDog/datadog-agent/blob/main/pkg/opentelemetry-mapping-go/otlp/attributes/attributes.go

string(semconv1_27.AWSECSClusterARNKey):   "ecs_cluster_name",

The upstream resourcedetection ECS detector only exposes aws.ecs.cluster.arn; there is no cluster-name attribute available to map instead (documentation.md). So the ARN is the only input, and the tag ends up holding an ARN despite its name.

Describe what you expected

ecs_cluster_name to hold the cluster name on both paths, i.e. the segment after :cluster/ extracted from the ARN when mapping aws.ecs.cluster.arn, matching what the ECS Fargate check already produces.

Steps to reproduce the issue

1. Run the Agent as an OTLP sidecar in an ECS Fargate task, with resource_detection (detectors: [env, ecs]) and the datadog exporter.
2. Send any span through it.
3. Compare ecs_cluster_name on the resulting spans with the same tag on ecs.fargate.* metrics from the Agent check in the same task.

Additional environment details

Current workaround on our side, a transform processor before export:

transform/ecs_cluster_name:
  error_mode: ignore
  trace_statements:
    - replace_pattern(resource.attributes["aws.ecs.cluster.arn"], "^.*:cluster/", "")

This works, but it means every DDOT user on ECS has to know about the mismatch and repeat it in three pipelines. Extracting the name inside the mapping would make the two collection paths agree by default.