Configuring the SDK with Environment Variables and Files: OTCA practice questions

Every SDK must offer programmatic configuration, and most also read a common set of environment variables. Support for these variables varies by language, so the compliance matrix is the place to check a specific SDK. Values are parsed in a fixed way. An empty value counts as unset. Booleans become true only for the case-insensitive string true, so setting OTEL_SDK_DISABLED=1 leaves the SDK enabled. Enum values are case-insensitive, and unknown values produce a warning and are ignored.

The resource is usually set first. OTEL_SERVICE_NAME sets service.name and wins over a service.name entry in OTEL_RESOURCE_ATTRIBUTES. That second variable takes comma-separated key=value pairs whose values are strings; commas and equals signs inside keys or values must be percent-encoded. Resource data provided in code has higher priority than the environment variable. If no service name is configured, the semantic conventions require unknown_service: followed by the executable name.

Sampling is controlled by OTEL_TRACES_SAMPLER, which defaults to parentbased_always_on. Other values include always_on, always_off, traceidratio and parentbased_traceidratio. OTEL_TRACES_SAMPLER_ARG supplies an argument such as a ratio between 0 and 1, but it is used only when OTEL_TRACES_SAMPLER is also set. Exporters are chosen per signal with OTEL_TRACES_EXPORTER, OTEL_METRICS_EXPORTER and OTEL_LOGS_EXPORTER, which all default to otlp. The value none turns off the automatically configured exporter for that signal, while console prints to standard output. For periodic metric export, OTEL_METRIC_EXPORT_INTERVAL defaults to 60000 milliseconds and OTEL_METRIC_EXPORT_TIMEOUT to 30000.

The OTLP exporter has its own family of variables. OTEL_EXPORTER_OTLP_PROTOCOL accepts grpc, http/protobuf and http/json, and the spec says the default should be http/protobuf unless an SDK keeps grpc for backward compatibility. Default endpoints are localhost on port 4317 for gRPC and 4318 for HTTP. With OTLP/HTTP, OTEL_EXPORTER_OTLP_ENDPOINT is a base URL to which v1/traces, v1/metrics or v1/logs is appended, but the signal-specific endpoint variables are used exactly as written. Headers use the key1=value1,key2=value2 format, and the default export timeout is ten seconds.

Limits protect memory. OTEL_ATTRIBUTE_COUNT_LIMIT defaults to 128 attributes, and attribute value length is unlimited unless configured. Model-specific variables such as OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT are checked before the general one.

Declarative configuration describes the whole SDK in a YAML file named by OTEL_CONFIG_FILE, which replaces the deprecated OTEL_EXPERIMENTAL_CONFIG_FILE. The schema is marked stable, but SDK support is still experimental. Once the file is in use, other environment variables are ignored unless the file references them with substitution syntax such as ${OTEL_EXPORTER_OTLP_ENDPOINT}.