After you set up the tracing library with your code and configure the Agent to collect APM data, optionally configure the tracing library as desired, including setting up Unified Service Tagging.

It is recommended to use DD_SERVICE, DD_ENV, and DD_VERSION to set env, service and version for your services. Refer to the Unified Service Tagging docummentation recommendations on which value to set for environment variables.

Environment variables

To configure the tracer using environment variables, set the variables before launching the instrumented application.

DD_SERVICE
Since: v0.1.0
Sets the service name.
DD_ENV
Since: v0.1.0
Example: prod, pre-prod, or staging
Adds the env tag with the specified value to all generated spans.
DD_VERSION
Since: v0.1.0
Example: 1.2.3, 6c44da20, 2020.02.13
Sets the version of the service.
DD_TAGS
Since: v0.1.0
Example: team:intake,layer:api,foo:bar
A comma separated list of key:value pairs to be added to all generated spans.
DD_AGENT_HOST
Since: v0.1.0
Default: localhost
Sets the host where traces are sent (the host running the Agent). Can be a hostname or an IP address. Ignored if DD_TRACE_AGENT_URL is set.
DD_TRACE_AGENT_PORT
Since: v0.1.0
Default: 8126
Sets the port where traces are sent (the port where the Agent is listening for connections). Ignored if DD_TRACE_AGENT_URL is set. If the Agent configuration sets receiver_port or DD_APM_RECEIVER_PORT to something other than the default 8126, then DD_TRACE_AGENT_PORT or DD_TRACE_AGENT_URL must match it.
DD_TRACE_AGENT_URL
Since: v0.1.0
Default: http://<DD_AGENT_HOST>:<DD_TRACE_AGENT_PORT> if they are set, or http://localhost:8126. Examples:
HTTP URL: http://localhost:8126
Unix Domain Socket: unix:///var/run/datadog/apm.socket

Sets the URL endpoint where traces are sent. Overrides DD_AGENT_HOST and DD_TRACE_AGENT_PORT if set. This URL supports HTTP, HTTPS, and Unix address schemes.
If the Agent configuration sets receiver_port or DD_APM_RECEIVER_PORT to something other than the default 8126, then DD_TRACE_AGENT_PORT or DD_TRACE_AGENT_URL must match it.
DD_TRACE_RATE_LIMIT
Since: 0.1.0
Default: 200
Maximum number of traces allowed to be submitted per second.
DD_TRACE_SAMPLE_RATE
Since: 0.1.0
Default: The Datadog Agent default rate or 1.0.
Sets the sampling rate for all generated traces. The value must be between 0.0 and 1.0 (inclusive). By default, the sampling rate is delegated to the Datadog Agent. If no sampling rate is set by the Datadog Agent, then the default is 1.0.
DD_TRACE_SAMPLING_RULES
Since: v0.1.0
Default: null
Examples:
Set the sample rate to 20%: [{"sample_rate": 0.2}]
Set the span sample rate to 50% for the service my-service and operation name http.request, up to 50 traces per second: '[{"service": "my-service", "name": "http.request", "sample_rate":0.5, "max_per_second": 50}]'

A JSON array of objects. Each object must have a sample_rate, and the name and service fields are optional. The sample_rate value must be between 0.0 and 1.0 (inclusive). Rules are applied in configured order to determine the trace’s sample rate.
For more information, see Ingestion Mechanisms.
DD_SPAN_SAMPLING_RULES
Version: v0.1.0
Default: null
A JSON array of objects. Rules are applied in configured order to determine the span’s sample rate. The sample_rate value must be between 0.0 and 1.0 (inclusive).
DD_SPAN_SAMPLING_RULES_FILE
Since: 0.1.0
Points to a JSON file that contains the span sampling rules. See DD_SPAN_SAMPLING_RULES for the rule format.
DD_PROPAGATION_STYLE
Since: 0.1.0
Comma separated list of propagation styles to use when extracting and injecting tracing context.
When multiple values are given, the order of matching is based on the order of values.
DD_TRACE_PROPAGATION_STYLE_INJECT
Since: v0.1.6
Default: datadog,tracecontext
Accepted values: datadog, tracecontext, b3
Comma separated list of propagation styles to use when injecting tracing context. When multiple values are given, the order of matching is based on the order of values.
DD_TRACE_PROPAGATION_STYLE_EXTRACT
Since: v0.1.6
Default: datadog,tracecontext
Accepted values: datadog, tracecontext, b3
Comma separated list of propagation styles to use when extracting tracing context. When multiple values are given, the order of matching is based on the order of values.
DD_TRACE_ENABLED
Since: 0.1.0
Default: true
Submit or not traces to the Datadog Agent.
When false, the library stop sending traces to the Datadog Agent. However, the library continues to generate traces, report telemetry and poll for remote configuration updates.
DD_TRACE_REPORT_HOSTNAME
Since: 0.1.0
Default: false
Adds the hostname tag with the result of gethostname.
DD_TRACE_STARTUP_LOGS
Since: 0.1.0
Default: true
Log the tracer configuration once the tracer is fully initialized.
DD_TRACE_128_BIT_TRACEID_GENERATION_ENABLED
Since: 0.1.6
Default: true
If true, the tracer will generate 128-bit trace IDs.
If false, the tracer will generate legacy 64-bit trace IDs.
DD_INSTRUMENTATION_TELEMETRY_ENABLED
Since: 0.1.12
Default: true
Datadog may collect environmental and diagnostic information about your system to improve the product. When false, telemetry data are not collected.
DD_REMOTE_CONFIGURATION_ENABLED
Since: 0.2.0
Default: true
Enable the capability that allows to remotely configure and change the behavior of the tracer.
When false this feature is disabled.
For more information, see Remote Configuration.
DD_REMOTE_CONFIG_POLL_INTERVAL_SECONDS
Since: 0.2.0
Default: 5
Sets how often, in seconds, the Datadog Agent is queried for Remote Configuration updates.
DD_TRACE_DELEGATE_SAMPLING
Version: 0.2.0
Default: false
If true, delegate trace sampling decision to a child service and prefer the resulting decision over its own, if appropriate.

Further Reading