Opentelemetry: OTLP metric exported to cloudwatch but with empty Namespace

[mgshirali]

Bug Report

Describe the bug
I am using opentelemetry input plugin along with cloudwatch_logs output. One of my applications is sending an OTLP formatted metric to fluent-bit.
I see that fluent-bit is exporting this metric to cloudwatch in aws/emf format. However, the namespace in the payload seems to be missing. This even after I have specified metric_namespace in the output.

To Reproduce

    [INPUT]
        Name Opentelemetry
        Listen 0.0.0.0
        Port 4318

[OUTPUT]
        Name cloudwatch_logs
        Match v1_metrics
        region eu-west-1
        log_group_name /fluent-poc-cluster
        log_stream_prefix fluent-poc-metrics
        auto_create_group On
        log_format json/emf
        metric_namespace "fluent-bit-metric"

Cloudwatch log

{
    "_aws": {
        "Timestamp": 1754322754701,
        "CloudWatchMetrics": [
            {
                "Namespace": "", <=== Missing!!!
                "Dimensions": [
                    []
                ],
                "Metrics": [
                    {
                        "Name": "sdk_custom_metric",
                        "StorageResolution": 60
                    }
                ]
            }
        ]
    },
    "prom_metric_type": "gauge",
    "sdk_custom_metric": 42
}

• Steps to reproduce the problem:
• Install fluent-bit as deployment using helm chart with input and output as defined above
• Send OTLP metric
• Check logs in AWS console

Expected behavior
Namespace should be present in aws/emf log. That will allow AWS to dynamically build the metric which is not happening at the moment.

Your Environment

• Version used: 4.0.4
• Configuration: OTLP input plugin and cloudwatch_logs output
• Environment name and version (e.g. Kubernetes? What version?): Kubernetes 1.32
• Server type and version: k8s
• Operating System and version: k8s
• Filters and plugins: NA

Additional context
Unable to view metrics on AWS console using Fluent Bit