Tracing in the Apollo Router

The Apollo Router supports OpenTelemetry, with exporters for:

• Jaeger
• Zipkin
• Datadog
• OpenTelemetry Protocol (OTLP) over HTTP or gRPC

The Apollo Router generates spans that include the various phases of serving a request and associated dependencies. This is useful for showing how response time is affected by:

• Sub-request response times
• Query shape (sub-request dependencies)
• Apollo Router post-processing

Span data is sent to a collector such as Jaeger, which can assemble spans into a gantt chart for analysis.

Common configuration

Trace config

In your router's YAML config file, the trace_config section contains common configuration that's used by all exporters. This section is optional, and it falls back on the values of environment variables specified by the OpenTelemetry spec if service_name is not set.

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telemetry:
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  tracing:
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    trace_config:
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      service_name: "router"
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      service_namespace: "apollo"
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      # Optional. Either a float between 0 and 1 or 'always_on' or 'always_off'
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      sampler: 0.1
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      # Optional. Use a parent based sampler. This enables remote spans help make a decision on if a span is sampeld or not.
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      # https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/trace/sdk.md#parentbased
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      parent_based_sampler: false
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      # Optional limits
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      max_attributes_per_event: 10
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      max_attributes_per_link: 10
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      max_attributes_per_span: 10
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      max_events_per_span: 10
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      max_links_per_span: 10
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      # Attributes particular to an exporter that have not
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      # been explicitly handled in Router configuration.
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      attributes:
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        some.config.attribute: "config value"

If service_name is set, then environment variables are not used. However, you can embed environment variables into your router config using Unix ${key:default} syntax.

If no environment variable is set and service_name is not present then router is used as the default service name.

Propagation

The propagation section allows you to configure which propagators are active in addition to those automatically activated by using an exporter.

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telemetry:
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  tracing:
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    propagation:
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      # https://www.w3.org/TR/baggage/
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      baggage: false
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      # https://www.datadoghq.com/
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      datadog: false
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      # https://www.jaegertracing.io/ (compliant with opentracing)
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      jaeger: false
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      # https://www.w3.org/TR/trace-context/
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      trace_context: false
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      # https://zipkin.io/ (compliant with opentracing)
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      zipkin: false
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      # If you have your own way to generate a trace id and you want to pass it via a custom request header
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      request:
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        header_name: my-trace-id

Specifying explicit propagation is generally only required if you're using an exporter that supports multiple trace ID formats (e.g., OpenTelemetry Collector, Jaeger, or OpenTracing compatible exporters).

Trace ID

If you want to expose in response headers the generated trace ID or the one you provided using propagation headers you can use this configuration:

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telemetry:
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  tracing:
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    experimental_response_trace_id:
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      enabled: true # default: false
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      header_name: "my-trace-id" # default: "apollo-trace-id"

Using this configuration you will have a response header called my-trace-id containing the trace ID. It could help you to debug a specific query if you want to grep your log with this trace id to have more context.

Batch Processor

All trace exporters (apollo|datadog|zipkin|jaeger|otlp) have batch span processor configuration, it will be necessary to tune this if you see the following in your logs:

OpenTelemetry trace error occurred: cannot send span to the batch span processor because the channel is full

• scheduled_delay The delay from receiving the first span to the batch being sent.
• max_concurrent_exports The maximum number of overlapping export requests. For instance if ingest is taking a long time to respond there may be several overlapping export requests.
• max_export_batch_size The number of spans to include in a batch. Your ingest may have max message size limits.
• max_export_timeout The timeout for sending spans before dropping the data.
• max_queue_size The maximum number of spans to be buffered before dropping span data.

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telemetry:
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  # Apollo tracing
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  apollo:
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    batch_processor:
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      scheduled_delay: 100ms
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      max_concurrent_exports: 1000
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      max_export_batch_size: 10000
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      max_export_timeout: 100s
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      max_queue_size: 10000
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  tracing:
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    # Datadog
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    datadog:
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      batch_processor:
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        scheduled_delay: 100ms
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        max_concurrent_exports: 1000
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        max_export_batch_size: 10000
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        max_export_timeout: 100s
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        max_queue_size: 10000
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      endpoint: default
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    # Jaeger
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    # Otlp
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    # Zipkin

You will need to experiment to find the setting that are appropriate for your use case.

Using Datadog

The Apollo Router can be configured to connect to either the default agent address or a URL.

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telemetry:
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  tracing:
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    datadog:
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      # Either 'default' or a URL
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      endpoint: default

Using Jaeger

The Apollo Router can be configured to export tracing data to Jaeger either via an agent or http collector.

Agent config

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telemetry:
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  tracing:
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    jaeger:
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      agent:
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        # Either 'default' or a URL
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        endpoint: docker_jaeger:14268

Collector config

If you're using Kubernetes, you can inject your secrets into configuration via environment variables:

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telemetry:
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  tracing:
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    jaeger:
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      collector:
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        endpoint: "http://my-jaeger-collector"
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        username: "${env.JAEGER_USERNAME}"
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        password: "${env.JAEGER_PASSWORD}"

OpenTelemetry Collector via OTLP

OpenTelemetry Collector is a horizontally scalable collector that you can use to receive, process, and export your telemetry data in a pluggable way.

If you find that the built-in telemetry features of the Apollo Router are missing some desired functionality (e.g., exporting to Kafka), then it's worth considering this option.

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telemetry:
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  tracing:
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    otlp:
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      # Either 'default' or a URL
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      endpoint: default
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      # Optional protocol (Defaults to grpc)
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      protocol: grpc
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      # Optional Grpc configuration
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      grpc:
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        domain_name: "my.domain"
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        key: ""
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        ca: ""
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        cert: ""
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        metadata:
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          foo: bar
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      # Optional Http configuration
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      http:
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        headers:
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          foo: bar

Remember that file. and env. prefixes can be used for expansion in config yaml. e.g. ${file.ca.txt}.

Using Zipkin

The Apollo Router can be configured to export tracing data to either the default collector address or a URL:

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telemetry:
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  tracing:
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    zipkin:
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      # Either 'default' or a URL
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      endpoint: http://my_zipkin_collector.dev