feat(instrumentation): add profiler_enabled to gate the continuous profiler (opt-out)

[kamranf]

Why

The continuous profiler is gated on instrumentation.enabled — the same flag that turns on APM tracing. So there is no way to keep tracing while turning the profiler off. That matters because the profiler bills per host, and in shared dev environments it inflates continuous-profiler host usage across many short-lived instances.

What

Add a dedicated profiler_enabled setting so the profiler can be turned off independently of tracing:

• config.go: add ProfilerEnabled bool (mapstructure:"profiler_enabled"), and default it to true in NewConfig (SetDefault("profiler_enabled", true)).
• profiler.go: the profiler runs when Enabled && ProfilerEnabled. With the default, this is identical to today's behaviour (profiler on wherever instrumentation is enabled).
• Tests: gating matrix in profiler_test.go; default-true + APP_DATADOG_PROFILER_ENABLED opt-out coverage in config_test.go.
• README: documents the opt-out.

Opt-out, not opt-in (backwards compatible)

Per review feedback: profiling is a deliberate default in Go SDK (cheap, valuable in prod). So this is opt-out — profiler_enabled defaults to true, and upgrading go-sdk does not change behaviour for any service. To disable the profiler while keeping tracing, set per environment:

# config/settings/datadog.yml
development:
  enabled: true
  profiler_enabled: false

or via env var APP_DATADOG_PROFILER_ENABLED=false.

Rollout

After release, go-sdk upgrades reach services via Go Chassis parity (profiler stays on by default). To stop dev/devkube profiling for api-gateway, add APP_DATADOG_PROFILER_ENABLED=false to its devkube-config deployment.

Verification

• CI build (go build + go test ./...).

---

Note

Medium Risk
Touches shared configuration loading for all Viper-backed configs and changes profiler startup gating; default-on preserves prod behavior but mis-set env/YAML could unexpectedly disable profiling in some environments.

Overview
Adds profiler_enabled so the DataDog continuous profiler can be turned off while APM tracing stays on, via YAML (profiler_enabled: false) or APP_DATADOG_PROFILER_ENABLED=false. The flag defaults to true, so existing services keep profiler-on-when-instrumentation-is-on behavior after upgrading.

NewProfiler now enables profiling only when Enabled && ProfilerEnabled (previously profiler followed Enabled alone).

The shared Viper builder applies SetDefault before AllKeys / BindEnv, so keys that exist only as defaults (not in the YAML file) still get env binding—required for profiler_enabled overrides without adding the key to every datadog.yml.

README profiling section documents the opt-out; tests cover default-true config, env opt-out, and the profiler gating matrix.

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Manual Config disables profiler

Medium Severity

NewProfiler now requires both config.Enabled and config.ProfilerEnabled, but only NewConfig defaults profiler_enabled to true. A hand-built Config with Enabled: true and an unset ProfilerEnabled leaves profiling off, whereas before this change the profiler followed Enabled alone.

 

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[kamranf]

Valid observation, but it does not occur in practice: instrumentation.Config is always produced by NewConfig() — directly, or via configuration.NewConfig() (pkg/configuration/configuration.go) which every consumer uses — and NewConfig defaults profiler_enabled to true. So a real caller always follows Enabled; only tests construct a Config{} literal, where the zero value is expected. Keeping the Enabled && ProfilerEnabled gate (rather than reading ProfilerEnabled alone) is deliberate so profiling never turns on where instrumentation is disabled. If we want to be defensive about hand-built configs too, I can switch the field to *bool (nil → follow Enabled), but that adds complexity for a path we do not use.

[Neurostep]

LGTM 🚀