Environment Variable Specification

Status: Mixed

The goal of this specification is to unify the environment variable names between different OpenTelemetry SDK implementations. SDKs MAY choose to allow configuration via the environment variables in this specification, but are not required to. If they do, they SHOULD use the names listed in this document.

Parsing empty value

Status: Stable

The SDK MUST interpret an empty value of an environment variable the same way as when the variable is unset.

Special configuration types

Status: Stable

Boolean value

Any value that represents a Boolean MUST be set to true only by the case-insensitive string "true", meaning "True" or "TRUE" are also accepted, as true. An SDK MUST NOT extend this definition and define additional values that are interpreted as true. Any value not explicitly defined here as a true value, including unset and empty values, MUST be interpreted as false. If any value other than a true value, case-insensitive string "false", empty, or unset is used, a warning SHOULD be logged to inform users about the fallback to false being applied. All Boolean environment variables SHOULD be named and defined such that false is the expected safe default behavior. Renaming or changing the default value MUST NOT happen without a major version upgrade.

Numeric value

If an SDK chooses to support an integer-valued environment variable, it SHOULD support nonnegative values between 0 and 2³¹ − 1 (inclusive). Individual SDKs MAY choose to support a larger range of values.

The following paragraph was added after stabilization and the requirements are thus qualified as “SHOULD” to allow SDKs to avoid breaking changes. For new implementations, these should be treated as MUST requirements.

For variables accepting a numeric value, if the user provides a value the SDK cannot parse, or which is outside the valid range for the configuration item, the SDK SHOULD generate a warning and gracefully ignore the setting, i.e., treat them as not set. In particular, SDKs SHOULD NOT assign a custom interpretation e.g. to negative values if a negative value does not naturally apply to a configuration and does not have an explicitly specified meaning, but treat it like any other invalid value.

For example, a value specifying a buffer size must naturally be non-negative. Treating a negative value as “buffer everything” would be an example of such a discouraged custom interpretation. Instead the default buffer size should be used.

Note that this could make a difference even if the custom interpretation is identical with the default value, because it might reset a value set from other configuration sources with the default.

Enum value

For variables which accept a known value out of a set, i.e., an enum value, SDK implementations MAY support additional values not listed here. For variables accepting an enum value, if the user provides a value the SDK does not recognize, the SDK MUST generate a warning and gracefully ignore the setting.

If a null object (empty, no-op) value is acceptable, then the enum value representing it MUST be "none".

Duration

Any value that represents a duration, for example a timeout, MUST be an integer representing a number of milliseconds. The value is non-negative - if a negative value is provided, the SDK MUST generate a warning, gracefully ignore the setting and use the default value if it is defined.

For example, the value 12000 indicates 12000 milliseconds, i.e., 12 seconds.

General SDK Configuration

Status: Stable

Name Description Default Notes
OTEL_SDK_DISABLED Disable the SDK for all signals false Boolean value. If “true”, a no-op SDK implementation will be used for all telemetry signals. Any other value or absence of the variable will have no effect and the SDK will remain enabled. This setting has no effect on propagators configured through the OTEL_PROPAGATORS variable.
OTEL_RESOURCE_ATTRIBUTES Key-value pairs to be used as resource attributes See Resource semantic conventions for details. See Resource SDK for more details.
OTEL_SERVICE_NAME Sets the value of the service.name resource attribute If service.name is also provided in OTEL_RESOURCE_ATTRIBUTES, then OTEL_SERVICE_NAME takes precedence.
OTEL_LOG_LEVEL Log level used by the SDK logger “info”
OTEL_PROPAGATORS Propagators to be used as a comma-separated list “tracecontext,baggage” Values MUST be deduplicated in order to register a Propagator only once.
OTEL_TRACES_SAMPLER Sampler to be used for traces “parentbased_always_on” See Sampling
OTEL_TRACES_SAMPLER_ARG String value to be used as the sampler argument The specified value will only be used if OTEL_TRACES_SAMPLER is set. Each Sampler type defines its own expected input, if any. Invalid or unrecognized input MUST be logged and MUST be otherwise ignored, i.e. the SDK MUST behave as if OTEL_TRACES_SAMPLER_ARG is not set.

Known values for OTEL_PROPAGATORS are:

Known values for OTEL_TRACES_SAMPLER are:

  • "always_on": AlwaysOnSampler
  • "always_off": AlwaysOffSampler
  • "traceidratio": TraceIdRatioBased
  • "parentbased_always_on": ParentBased(root=AlwaysOnSampler)
  • "parentbased_always_off": ParentBased(root=AlwaysOffSampler)
  • "parentbased_traceidratio": ParentBased(root=TraceIdRatioBased)
  • "parentbased_jaeger_remote": ParentBased(root=JaegerRemoteSampler)
  • "jaeger_remote": JaegerRemoteSampler
  • "xray": AWS X-Ray Centralized Sampling (third party)

Depending on the value of OTEL_TRACES_SAMPLER, OTEL_TRACES_SAMPLER_ARG may be set as follows:

  • For traceidratio and parentbased_traceidratio samplers: Sampling probability, a number in the [0..1] range, e.g. “0.25”. Default is 1.0 if unset.
  • For jaeger_remote and parentbased_jaeger_remote: The value is a comma separated list:
    • endpoint: the endpoint in form of scheme://host:port of gRPC server that serves the sampling strategy for the service (sampling.proto).
    • pollingIntervalMs: in milliseconds indicating how often the sampler will poll the backend for updates to sampling strategy.
    • initialSamplingRate: in the [0..1] range, which is used as the sampling probability when the backend cannot be reached to retrieve a sampling strategy. This value stops having an effect once a sampling strategy is retrieved successfully, as the remote strategy will be used until a new update is retrieved.
    • Example: endpoint=http://localhost:14250,pollingIntervalMs=5000,initialSamplingRate=0.25

Batch Span Processor

Status: Stable

Name Description Default Notes
OTEL_BSP_SCHEDULE_DELAY Delay interval (in milliseconds) between two consecutive exports 5000
OTEL_BSP_EXPORT_TIMEOUT Maximum allowed time (in milliseconds) to export data 30000
OTEL_BSP_MAX_QUEUE_SIZE Maximum queue size 2048
OTEL_BSP_MAX_EXPORT_BATCH_SIZE Maximum batch size 512 Must be less than or equal to OTEL_BSP_MAX_QUEUE_SIZE

Batch LogRecord Processor

Status: Stable

Name Description Default Notes
OTEL_BLRP_SCHEDULE_DELAY Delay interval (in milliseconds) between two consecutive exports 1000
OTEL_BLRP_EXPORT_TIMEOUT Maximum allowed time (in milliseconds) to export data 30000
OTEL_BLRP_MAX_QUEUE_SIZE Maximum queue size 2048
OTEL_BLRP_MAX_EXPORT_BATCH_SIZE Maximum batch size 512 Must be less than or equal to OTEL_BLRP_MAX_QUEUE_SIZE

Attribute Limits

SDKs SHOULD only offer environment variables for the types of attributes, for which that SDK implements truncation mechanism.

See the SDK Attribute Limits section for the definition of the limits.

Name Description Default Notes
OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT Maximum allowed attribute value size no limit
OTEL_ATTRIBUTE_COUNT_LIMIT Maximum allowed attribute count 128

Span Limits

Status: Stable

See the SDK Span Limits section for the definition of the limits.

Name Description Default Notes
OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT Maximum allowed attribute value size no limit
OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT Maximum allowed span attribute count 128
OTEL_SPAN_EVENT_COUNT_LIMIT Maximum allowed span event count 128
OTEL_SPAN_LINK_COUNT_LIMIT Maximum allowed span link count 128
OTEL_EVENT_ATTRIBUTE_COUNT_LIMIT Maximum allowed attribute per span event count 128
OTEL_LINK_ATTRIBUTE_COUNT_LIMIT Maximum allowed attribute per span link count 128

LogRecord Limits

Status: Stable

See the SDK LogRecord Limits section for the definition of the limits.

Name Description Default Notes
OTEL_LOGRECORD_ATTRIBUTE_VALUE_LENGTH_LIMIT Maximum allowed attribute value size no limit
OTEL_LOGRECORD_ATTRIBUTE_COUNT_LIMIT Maximum allowed log record attribute count 128

OTLP Exporter

See OpenTelemetry Protocol Exporter Configuration Options.

Zipkin Exporter

Status: Stable

Name Description Default
OTEL_EXPORTER_ZIPKIN_ENDPOINT Endpoint for Zipkin traces http://localhost:9411/api/v2/spans
OTEL_EXPORTER_ZIPKIN_TIMEOUT Maximum time (in milliseconds) the Zipkin exporter will wait for each batch export 10000

Additionally, the following environment variables are reserved for future usage in Zipkin Exporter configuration:

  • OTEL_EXPORTER_ZIPKIN_PROTOCOL

This will be used to specify whether or not the exporter uses v1 or v2, json, thrift or protobuf. As of 1.0 of the specification, there is no specified default, or configuration via environment variables.

Prometheus Exporter

Status: Experimental

Name Description Default
OTEL_EXPORTER_PROMETHEUS_HOST Host used by the Prometheus exporter “localhost”
OTEL_EXPORTER_PROMETHEUS_PORT Port used by the Prometheus exporter 9464

Exporter Selection

Status: Stable

We define environment variables for setting one or more exporters per signal.

Name Description Default
OTEL_TRACES_EXPORTER Trace exporter to be used “otlp”
OTEL_METRICS_EXPORTER Metrics exporter to be used “otlp”
OTEL_LOGS_EXPORTER Logs exporter to be used “otlp”

The SDK MAY accept a comma-separated list to enable setting multiple exporters.

Known values for OTEL_TRACES_EXPORTER are:

  • "otlp": OTLP
  • "zipkin": Zipkin (Defaults to protobuf format)
  • "none": No automatically configured exporter for traces.

Known values for OTEL_METRICS_EXPORTER are:

  • "otlp": OTLP
  • "prometheus": Prometheus
  • "none": No automatically configured exporter for metrics.

Known values for OTEL_LOGS_EXPORTER are:

  • "otlp": OTLP
  • "none": No automatically configured exporter for logs.

Metrics SDK Configuration

Status: Mixed

Exemplar

Status: Experimental

Name Description Default Notes
OTEL_METRICS_EXEMPLAR_FILTER Filter for which measurements can become Exemplars. "trace_based"

Known values for OTEL_METRICS_EXEMPLAR_FILTER are:

Periodic exporting MetricReader

Status: Stable

Environment variables specific for the push metrics exporters (OTLP, stdout, in-memory) that use periodic exporting MetricReader.

Name Description Default Notes
OTEL_METRIC_EXPORT_INTERVAL The time interval (in milliseconds) between the start of two export attempts. 60000
OTEL_METRIC_EXPORT_TIMEOUT Maximum allowed time (in milliseconds) to export data. 30000

Language Specific Environment Variables

To ensure consistent naming across projects, this specification recommends that language specific environment variables are formed using the following convention:

OTEL_{LANGUAGE}_{FEATURE}