Default resource not included in v0.32.0 compared to v0.31.0

[jsign]

Description

Between versions v0.31.0 and v0.32.0, the attributes from the default resource changed their behavior.

Environment

• OS: Linux
• Architecture: amd64
• Go Version: 1.10
• opentelemetry-go version:v0.31.0 -> v0.32.0

Steps To Reproduce

• git checkout metric/v0.31.0
• cd example/prometheus && go run main.go
• See the output of loalhost:2222/metrics

Do the same with metric/v0.32.0 and compare the third bullet step output.

Expected behavior

The v0.31.0 version outputs:

# HELP ex_com_one 
# TYPE ex_com_one gauge
ex_com_one{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0"} 1
# HELP ex_com_three 
# TYPE ex_com_three counter
ex_com_three{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0"} 12
# HELP ex_com_two 
# TYPE ex_com_two histogram
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0",le="1"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0",le="2"} 0
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0",le="5"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0",le="10"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0",le="20"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0",le="50"} 1
ex_com_two_bucket{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0",le="+Inf"} 1
ex_com_two_sum{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0"} 2
ex_com_two_count{A="1",B="2",C="3",ex_com_lemons="10",service_name="unknown_service:main",telemetry_sdk_language="go",telemetry_sdk_name="opentelemetry",telemetry_sdk_version="1.8.0"} 1

So we see the service_name, telemetry_sdk_language, and other default attributes from the default resource.

When running in v0.32.0:

# HELP bar a fun little gauge
# TYPE bar counter
bar{A="B",C="D"} 75
# HELP baz a very nice histogram
# TYPE baz histogram
baz_bucket{A="B",C="D",le="0"} 0
baz_bucket{A="B",C="D",le="5"} 0
baz_bucket{A="B",C="D",le="10"} 1
baz_bucket{A="B",C="D",le="25"} 1
baz_bucket{A="B",C="D",le="50"} 0
baz_bucket{A="B",C="D",le="75"} 0
baz_bucket{A="B",C="D",le="100"} 0
baz_bucket{A="B",C="D",le="250"} 2
baz_bucket{A="B",C="D",le="500"} 0
baz_bucket{A="B",C="D",le="1000"} 0
baz_bucket{A="B",C="D",le="+Inf"} 4
baz_sum{A="B",C="D"} 236
baz_count{A="B",C="D"} 4
# HELP foo a simple counter
# TYPE foo counter
foo{A="B",C="D"} 5

We don't see the attributes of the default resource.

I'm unsure if this is a bug or an undocumented change. If isn't a bug, which is the right way to add the original default resource?

[MrAlias]

The old way of adding those labels to every metric was indeed a bug. It is specifically called out as something that MUST NOT be done in the specification:

In SDK Prometheus (pull) exporters, resource attributes SHOULD be converted to a single target_info metric; otherwise, they MUST be dropped, and MUST NOT be attached as labels to other metric families. The target_info metric MUST be an info-typed metric whose labels MUST include the resource attributes, and MUST NOT include any other labels. There MUST be at most one target_info metric exposed on an SDK Prometheus endpoint.

It seems like a good addition to add a target_info metric to expose the resource information in the exporter.

[fatsheep9146]

@MrAlias Could I take this issue?

[fatsheep9146]

@Aneurysm9
I have talked with @paivagustavo in slack and found that he has already completed the coding of this pr, since this is duplicate of #3166.
Could you assign this work to @paivagustavo?