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Tracing

Tracing across the stack follows, as much as possible, the Open Telemetry specifications. Configuration environment variables are specified in the OpenTelemetry Environment Variable Specification.

We use the opentelemetry-go package, which currently does not have default support for the OTEL_TRACES_EXPORTER environment variables. Therefore, we provide some helper functions under boxo/tracing to support these.

In this document, we document the quirks of our custom support for the OTEL_TRACES_EXPORTER, as well as examples on how to use tracing, create traceable headers, and how to use the Jaeger UI. The Gateway examples fully support Tracing.

Environment Variables

For advanced configurations, such as ratio-based sampling, please see also the OpenTelemetry Environment Variable Specification.

OTEL_TRACES_EXPORTER

Specifies the exporters to use as a comma-separated string. Each exporter has a set of additional environment variables used to configure it. The following values are supported:

  • otlp
  • zipkin
  • stdout
  • file -- appends traces to a JSON file on the filesystem

Default: "" (no exporters)

OTLP Exporter

Unless specified in this section, the OTLP exporter uses the environment variables documented in OpenTelemetry Protocol Exporter.

OTEL_EXPORTER_OTLP_PROTOCOL

Specifies the OTLP protocol to use, which is one of:

  • grpc
  • http/protobuf

Default: "grpc"

Zipkin Exporter

See Zipkin Exporter.

File Exporter

OTEL_EXPORTER_FILE_PATH

Specifies the filesystem path for the JSON file.

Default: "$PWD/traces.json"

OTEL_PROPAGATORS

See General SDK Configuration.

Using Jaeger UI

One can use the jaegertracing/all-in-one Docker image to run a full Jaeger stack and configure the Kubo daemon, or gateway examples, to publish traces to it. Here, in an ephemeral container:

$ docker run -d --rm --name jaeger \
  -e COLLECTOR_OTLP_ENABLED=true \
  -e COLLECTOR_ZIPKIN_HOST_PORT=:9411 \
  -p 5775:5775/udp \
  -p 6831:6831/udp \
  -p 6832:6832/udp \
  -p 5778:5778 \
  -p 16686:16686 \
  -p 14250:14250 \
  -p 14268:14268 \
  -p 14269:14269 \
  -p 4317:4317 \
  -p 4318:4318 \
  -p 9411:9411 \
  jaegertracing/all-in-one

Then, in other terminal, start the app that uses boxo/tracing internally (e.g., a Kubo daemon), with Jaeger exporter enabled:

$ OTEL_EXPORTER_OTLP_INSECURE=true OTEL_TRACES_EXPORTER=otlp ipfs daemon --init

Finally, the Jaeger UI is available at http://localhost:16686.

Generate traceparent Header

If you want to trace a specific request and want to have its tracing ID, you can generate a Traceparent header. According to the Trace Context specification, the header is formed as follows:

version-format   = trace-id "-" parent-id "-" trace-flags
trace-id         = 32HEXDIGLC  ; 16 bytes array identifier. All zeroes forbidden
parent-id        = 16HEXDIGLC  ; 8 bytes array identifier. All zeroes forbidden
trace-flags      = 2HEXDIGLC   ; 8 bit flags. Currently, only one bit is used. See below for details

To generate a valid Traceparent header value, the following script can be used:

version="00" # fixed in spec at 00
trace_id="$(cat /dev/urandom | tr -dc 'a-f0-9' | fold -w 32 | head -n 1)"
parent_id="00$(cat /dev/urandom | tr -dc 'a-f0-9' | fold -w 14 | head -n 1)"
trace_flag="01"   # sampled
traceparent="$version-$trace_id-$parent_id-$trace_flag"
echo $traceparent

NOTE: the tr command behaves differently on macOS. You may want to install the GNU tr (gtr) and use it instead.

Then, the value can be passed onto the request with curl -H "Traceparent: $traceparent" URL. If using Jaeger, you can now search by the trace with ID $trace_id and see the complete trace of this request.