The SDK is an implementation of the OpenTelemetry API and should be included in your final deployable artifact (usually an OTP Release).
The SDK starts up its supervision tree on boot, so initial configuration must be
done through the Application or OS environment
variables.
The following example configurations show configuring the SDK to use the batch
span processor which then exports through the OpenTelemetry
Protocol
over HTTP to http://localhost:4318
, encoding the Spans with protobufs.
[
{opentelemetry,
[{span_processor, batch},
{traces_exporter, otlp}]},
{opentelemetry_exporter,
[{otlp_protocol, http_protobuf},
{otlp_endpoint, "http://localhost:4318"}]}]}
].
config :opentelemetry,
span_processor: :batch,
traces_exporter: :otlp
config :opentelemetry_exporter,
otlp_protocol: :http_protobuf,
otlp_endpoint: "http://localhost:4318"
If your exporting pipeline is not ready, you may disable trace exporting to prevent memory overflows.
This can be done by setting traces_exporter
's value to the atom none
.
[
{opentelemetry,
[{traces_exporter, none}]}
].
config :opentelemetry, traces_exporter: :none
The following sections detail the available SDK options and how to configure them through either the OS or Application environment.
Spans are created by Tracers and each Tracer is associated with a name and version. The name and version can be anything, but the macros provided by the API will always use a Tracer with name/version of the OTP Application the macro is used in. To facilitate this a Tracer is created for each available Application when the SDK boots. It relies on mapping modules to Applications, so if there is a huge number of modules in a Release the time to create all these Tracers can become more than you want to wait on boot.
OS | Application | Default | Type |
---|---|---|---|
OTEL_CREATE_APPLICATION_TRACERS | create_application_tracers | true | boolean |
Disabling the creation of Tracers at start-up means when the macros are used to start Spans the name and version of the Tracer creating those Spans will be undefined, but everything will continue to work as before.
Sampling is a mechanism to control the number of traces collected and sent to the backend. A Sampler is responsible for making a decision on whether to sample a trace or not.
This decision happens when starting a span. For this reason, only the initial attributes passed to with_span
or start_span
are available to the Sampler. Attributes added within with_span
or between start_span
and end_span
calls don't affect the outcome as the decision to sample or not has already been made.
There are several built-in samplers available, and it's possible to create custom samplers.
OS | Application | Default | Type |
---|---|---|---|
OTEL_TRACES_SAMPLER | sampler | parentbased_always_on | always_on, always_off, traceidratio, parentbased_always_on, parentbased_always_off, parentbased_traceidratio |
OTEL_TRACES_SAMPLER_ARG | sampler | String. Each Sampler type defines its own expected input, if any. |
To create a custom sampler, implement a module with behaviour otel_sampler
, and then install your custom sampler when configuring the opentelemetry
application
defmodule MySampler do
require OpenTelemetry.Tracer, as: Tracer
@behaviour :otel_sampler
@impl :otel_sampler
def setup(_sampler_opts) do
[]
end
@impl :otel_sampler
def description(_sampler_config) do
"MySampler"
end
@impl :otel_sampler
def should_sample(
ctx,
_trace_id,
_links,
_span_name,
_span_kind,
_attributes,
_sampler_config
) do
sample_decision = ... # custom logic to determine whether to sample or not
tracestate = Tracer.current_span_ctx(ctx) |> OpenTelemetry.Span.tracestate()
case sample_decision do
true -> {:record_and_sample, [], tracestate}
false -> {:drop, [], tracestate}
end
end
end
config :opentelemetry,
sampler: {:parent_based, %{root: {MySampler, %{my_config_arg: 1}}}},
span_processor: :batch,
traces_exporter: :otlp
Propagators define how to inject and extract context in requests to or from
external services. A propagator that works on key/value pairs of text, like HTTP
headers, can be any module that implements the otel_propagator_text_map
behaviour. There are 4 built-in propagators that are part of the API:
- tracecontext: Encodes the Trace
context as headers
traceparent
andtracestate
. - baggage: Encodes
baggage
elements as a comma delimited list under header key
baggage
. - b3multi: The
propagation format from Zipkin that breaks the context across multiple
headers,
X-B3-TraceId
,X-B3-SpanId
andX-B3-Sampled
. - b3: The
propagation format from Zipkin that encodes to a single header
b3
.
OS | Application | Default | Type |
---|---|---|---|
OTEL_PROPAGATORS | text_map_propagators | [tracecontext,baggage] | List of propagators (tracecontext , baggage , b3multi , b3 ) |
Span
processors
are invoked when a Span is started and when it ends. The default processor is
the batch processor (otel_batch_processor
) -- also available is the simple
processor (otel_simple_processor
) which blocks on every finished Span until it
is exported.
The batch processor waits bsp_scheduled_delay_ms
milliseconds or until the buffer of
finished Spans reaches bsp_max_queue_size
and then exports the spans together.
The export is canceled if it takes longer than bsp_exporting_timeout_ms
.
OS | Application | Default | Type |
---|---|---|---|
OTEL_BSP_SCHEDULE_DELAY_MILLIS | bsp_scheduled_delay_ms | 5000 | integer |
OTEL_BSP_EXPORT_TIMEOUT_MILLIS | bsp_exporting_timeout_ms | 30000 | integer |
OTEL_BSP_MAX_QUEUE_SIZE | bsp_max_queue_size | 2048 | integer |
Resources capture information about the environment the program is running in. For example, a process producing telemetry that is running in a container on Kubernetes has a Pod name, it is in a namespace and possibly is part of a Deployment which also has a name. All three of these attributes can be included in the Resource.
OS | Application | Default | Type |
---|---|---|---|
OTEL_RESOURCE_DETECTORS | resource_detectors | [otel_resource_env_var, otel_resource_app_env] | list of modules |
OTEL_RESOURCE_DETECTOR_TIMEOUT | resource_detector_timeout | 5000 | integer |
The default detectors read resource attributes from the OS environment variable
OTEL_RESOURCE_ATTRIBUTES
and Application environment variable resource
.
The number of Attributes, Events and Links on a Span are limited, as well as the length of an Attribute's value. When the limit is reached any additional Attributes, Events or Links are dropped and Attribute values larger than the length limit are truncated.
OS | Application | Default | Type |
---|---|---|---|
OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT | attribute_count_limit | 128 | integer |
OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT | attribute_value_length_limit | infinity | integer | infinity |
OTEL_SPAN_EVENT_COUNT_LIMIT | event_count_limit | 128 | integer |
OTEL_SPAN_LINK_COUNT_LIMIT | link_count_limit | 128 | integer |
OTEL_EVENT_ATTRIBUTE_COUNT_LIMIT | attribute_per_event_limit | 128 | integer |
OTEL_LINK_ATTRIBUTE_COUNT_LIMIT | attribute_per_link_limit | 128 | integer |
Read more in the specification about Span limits and Attribute limits.
Because of Erlang's "Let It Crash" philosophy it is possible that at some point
a Span will never have end_span
called. To handle these cases the SDK includes
a process that will periodically check the active Span table for Spans that are
older than the span_ttl
and will drop or end the Span depending on the
configured strategy
. The failed_attribute_and_end_span
strategy will add the
attribute finished_by_sweeper
with value true
to the Span before calling
end_span
.
The sweeper's configuration is a map under environment key sweeper
.
OS | Application | Default | Type |
---|---|---|---|
OTEL_SPAN_SWEEPER_INTERVAL | interval | 600000 | integer | infinity |
OTEL_SPAN_SWEEPER_STRATEGY | strategy | drop | drop | end_span | failed_attribute_and_end_span | fun/1 |
OTEL_SPAN_SWEEPER_SPAN_TTL | span_ttl | 1800000 | integer | infinity |
OTEL_SPAN_SWEEPER_STORAGE_SIZE | storage_size | infinity | integer | infinity |
Read OpenTelemetry project contributing guide for general information about the project.