Otel declarative config

OpenTelemetry Declarative Configuration

Declarative configuration replaces scattered OTEL_* environment variables and language-specific programmatic SDK setup with a single YAML file. One file configures all SDK components: tracer provider, meter provider, logger provider, propagators, and resource.

For the current per-language SDK status, fetch the SDK compatibility matrix (see Sources of Truth). Use it to understand implementation coverage, not as the only source for YAML literals.

Sources of Truth

This skill teaches concepts. The schema itself, valid file_format strings, field names, and SDK compatibility evolve per release — fetch from upstream rather than relying on embedded copies. Cache results for the conversation; refetch only on schema-related errors.

Fact	Fetch
Latest schema release tag	gh release view --repo open-telemetry/opentelemetry-configuration --json tagName,publishedAt
SDK ↔ schema compatibility matrix (coverage advisory, not authoritative for literal file_format)	WebFetch https://raw.githubusercontent.com/open-telemetry/opentelemetry-configuration/main/language-support-status.md
Field-by-field docs for the latest release	WebFetch https://raw.githubusercontent.com/open-telemetry/opentelemetry-configuration/<schema-release-tag>/schema-docs.md
Compiled JSON Schema (validate generated YAML against this)	WebFetch https://raw.githubusercontent.com/open-telemetry/opentelemetry-configuration/<schema-release-tag>/opentelemetry_configuration.json
Canonical full example	WebFetch https://raw.githubusercontent.com/open-telemetry/opentelemetry-configuration/<schema-release-tag>/examples/otel-sdk-config.yaml
Migration template (every option, with comments)	WebFetch https://raw.githubusercontent.com/open-telemetry/opentelemetry-configuration/<schema-release-tag>/examples/otel-sdk-migration-config.yaml
Schema CHANGELOG (breaking-change history with migration steps)	WebFetch https://raw.githubusercontent.com/open-telemetry/opentelemetry-configuration/<schema-release-tag>/CHANGELOG.md

Workflow when generating YAML:

1. Identify the exact runtime/package/agent version that will parse the file.
2. Fetch that runtime/package source, docs, or test fixtures and confirm the accepted file_format literal. If this conflicts with language-support-status.md, the runtime/package wins.
3. Fetch examples/otel-sdk-config.yaml → use as the structural template only after adapting the file_format and fields to the selected runtime/package.
4. Overlay the user's specific values (service name, endpoint, sampling, headers).
5. If validation matters, fetch opentelemetry_configuration.json and validate the result, then still verify against the selected runtime/package because SDK implementations may lag or differ from the schema repository.

Replace <schema-release-tag> with the tag returned by the first fetch. Keep the compatibility matrix on main: it tracks language implementation coverage independently of schema releases and may include work not yet released by an implementation. Do not use schema files or examples from main to generate released-version guidance.

The "Latest supported file format" values in language-support-status.md are schema/version coverage metadata. Do not mechanically copy them into YAML unless the target SDK parser, agent docs, or package fixtures prove that exact literal is accepted.

Terminology trap: schema coverage identifiers and YAML file_format literals are related, but not interchangeable. A matrix entry uses a full semver-shaped coverage value (e.g. 1.0.0, or a pre-release such as 1.0.0-rc.3 for implementations still tracking an older schema), while stable schema examples use a MAJOR.MINOR string such as 1.0 or 1.1. Older implementations may accept or require a pre-release literal, and released parsers do not all enforce versions identically. Generated YAML must use the literal verified in the target runtime. Schema release v1.1.0 examples use file_format: "1.1"; treat that as release-specific, not a permanent default, and confirm the latest release with the gh release fetch above.

For language-specific package versions and SDK API surface, see the Sources of Truth section in each language's otel-<lang> skill (otel-go, otel-java, otel-js, otel-python). otel-dotnet is listed in Cross-References below but does not support declarative YAML config yet — see the .NET note.

Python note: declarative config was introduced in opentelemetry-sdk 1.43.0. As of Python 1.44.0 / 0.65b0, it lives in the experimental opentelemetry-configuration package; install that package directly for new setups. The opentelemetry-sdk[file-configuration] extra remains as a deprecated compatibility alias. Released Python SDKs honor OTEL_CONFIG_FILE through the SDK configurator; when set, the file is authoritative and the env-var initialization path is skipped. Programmatic loading is available from the public opentelemetry.configuration namespace. See the otel-python skill and its declarative-setup.md reference.

.NET note: declarative YAML config is not yet implemented in OpenTelemetry .NET (tracked by open-telemetry/opentelemetry-dotnet#6380). .NET configures via the DI/builder API, OTEL_* env vars, and IConfiguration. Do not use OTEL_CONFIG_FILE with .NET runtimes. See the otel-dotnet skill and its setup.md reference.

Activation

The standard environment variable is OTEL_CONFIG_FILE:

export OTEL_CONFIG_FILE=/app/configs/otel.yaml

Setting the variable alone does not bootstrap every language. When the selected language's declarative bootstrap or autoconfigure path runs, it reads this file at startup. In file-config mode, SDKs ignore OTEL_* environment variables except those referenced through environment-variable substitution inside the config file.

Language-specific activation varies — see the language sdk-setup skills for details.

Environment Variable Substitution

The table and rules below describe the stable file-format specification. Runtime implementations can lag the specification, so test substitution behavior with the exact SDK release that will load the file.

Syntax	Behavior
${VAR}	Substitute with value of VAR
${env:VAR}	Same as ${VAR} (explicit prefix)
${VAR:-default}	Use default if VAR is unset or empty
$$	Escape sequence, resolves to literal $

Rules:

• Substitution applies only to scalar values, not mapping keys
• Type coercion happens after substitution (${BOOL} where BOOL=true becomes boolean)
• No recursive substitution
• Invalid references produce a parse error

Released implementation qualifications: Go otelconf 0.24.0 expands references in mapping keys. OpenTelemetry Java 1.64.0 still leaves scalar sequence items unsubstituted and treats invalid references such as ${VAR&} as literal text. Python opentelemetry-configuration 0.65b0 does not recognize ${env:VAR}, expands references in mapping keys, and leaves invalid references as literal text. Keep substitutions in scalar values, prefer ${VAR} for portable files, and verify the target SDK parser; structural schema validation does not prove these behaviors.

Configuration Interaction

Declarative configuration is a file-config mode, not a lower-precedence layer under OTEL_* environment variables:

Mode	Behavior
File config (OTEL_CONFIG_FILE, -Dotel.config.file, or programmatic loader)	The file supplies SDK configuration. OTEL_* env vars are ignored unless the file explicitly references them with substitution such as ${OTEL_SERVICE_NAME}.
Env-var config	Applies only when the selected SDK/runtime is not parsing a declarative config file.
Programmatic setup	Application code can still decide whether to load a file, override parsed values, or build providers directly. Treat the programmatic code path as the runtime source of truth.

Cross-References

• Language-specific setup: otel-go, otel-java, otel-js, otel-python (each loads its own references/declarative-setup.md); otel-dotnet (declarative YAML config not yet supported — see .NET note above).