Clarify default sampler (#284)

Author: seemk

CHANGELOG.md

@@ -12,12 +12,19 @@
 
 #### Enhancements
 
-- Require a CLA Assistant GitHub workflow. (#269)
-- Update the CLA notice in `CONTRIBUTING.md` template. (#269, #274)
-- Add Renovate as an acceptable alternative to Dependabot. (#271)
+- Clarify the default sampling algorithm.
+  [#284](https://github.com/signalfx/gdi-specification/pull/284)
+- Require a CLA Assistant GitHub workflow.
+  [#269](https://github.com/signalfx/gdi-specification/pull/269)
+- Update the CLA notice in `CONTRIBUTING.md` template.
+  [#269](https://github.com/signalfx/gdi-specification/pull/269)
+  [#274](https://github.com/signalfx/gdi-specification/pull/274)
+- Add Renovate as an acceptable alternative to Dependabot.
+  [#271](https://github.com/signalfx/gdi-specification/pull/271)
 - Add disk buffering configuration options for RUM mobile instrumentation
-  libraries. (#275)
-- Update telemetry resource attributes (#277):
+  libraries. [#275](https://github.com/signalfx/gdi-specification/pull/275)
+- Update telemetry resource attributes
+  [#277](https://github.com/signalfx/gdi-specification/pull/277):
   - Deprecate `splunk.distro.version`,
   - Change `telemetry.auto.version` to `telemetry.distro.version`,
   - Add `telemetry.distro.name` resource attribute.

specification/configuration.md

@@ -244,6 +244,10 @@ are required.
     telemetry directly to Splunk Observability Cloud.
     ```
 
+- `OTEL_TRACES_SAMPLER`
+  - Distribution MUST default to `always_on`
+    (not OpenTelemetry default)
+
 In addition to environment variables, other ways of defining configuration also exist:
 
 - [Java System