Pass through Datadog environment variables to Nginx when EnableOpentracing+DatadogCollectorHost set

[ellieayla]

Is this a request for help? (If yes, you should use our troubleshooting guide and community support channels, see https://kubernetes.io/docs/tasks/debug-application-cluster/troubleshooting/.):

What keywords did you search in NGINX Ingress controller issues before filing this one? (If you have found any duplicates, you should instead reply there.):

---

Is this a BUG REPORT or FEATURE REQUEST? (choose one): Feature

NGINX Ingress controller version: 0.26.0

Kubernetes version (use kubectl version):

Environment:

• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release):
• Kernel (e.g. uname -a):
• Install tools:
• Others:

What happened:

After #4371 merged, the dd-opentracing-cpp module detects several environment variables and configures tracer behaviour based on their values.

• Added DD_ENV environment variable DataDog/dd-opentracing-cpp#103 enabled DD_ENV
• Add support for setting trace analytics via environment variables. DataDog/dd-opentracing-cpp#104 enabled DD_GLOBAL_ANALYTICS_SAMPLE_RATE and DD_TRACE_ANALYTICS_ENABLED

Setting those environment variables in the dd-opentracing-cpp requires setting them in the ingress-nginx pod (very reasonable) and requires whitelisting them for passthrough in a custom nginx template or main-snippet like

main-snippet: |
    env DD_ENV;
    env DD_TRACE_ANALYTICS_ENABLED;

What you expected to happen:

Generate nginx.conf correctly without repeating config in multiple places.

How to reproduce it (as minimally and precisely as possible):

Build ingress-nginx from master after #4371 merged, set environment variable DD_TRACE_ANALYTICS_ENABLED=true on the ingress-nginx Pod, don't see trace-analytics enabled in dd-opentracing-cpp because nginx doesn't pass it through by default. Read http://nginx.org/en/docs/ngx_core_module.html#env and define a custom main-snippet as above. Be happier.

Anything else we need to know:

I'm going to make a PR for this, unless someone beats me to it.

[ellieayla]

On further investigation, it looks like all of these configuration options can also be set in /etc/nginx/opentracing.json, read by https://github.com/DataDog/dd-opentracing-cpp/blob/11311abc9160ceee63cfdb2e027e82f48a5348a0/src/tracer_factory.cpp#L14-L86

Some of those options are exposed by the existing

ingress-nginx/internal/ingress/controller/nginx.go

Lines 1055 to 1060 in 771fc9f

	const datadogTmpl = `{
	"service": "{{ .DatadogServiceName }}",
	"agent_host": "{{ .DatadogCollectorHost }}",
	"agent_port": {{ .DatadogCollectorPort }},
	"operation_name_override": "{{ .DatadogOperationNameOverride }}"
	}`

The correct approach is probably to populate the remaining options here, and not deal in environment variables.

[ellieayla]

Hang on, is DD_TRACE_ANALYTICS_ENABLED configurable via json file at all, or only by environment variable? Sure looks like the latter. That's unexpected.

[cgilmour]

Correct. In some cases, it's only via environment variable instead of config file or tracer options (code that initializes a tracer). No strong reason for it, but the intention was to make things easier for users and projects consuming the tracer. Eg. avoiding the need to add new code.

In this case though, it's making things harder.

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[k8s-ci-robot]

@fejta-bot: Closing this issue.

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