OpenTelemetry instrumentation for cowboy.

Semantic Conventions

All required and recommended Server HTTP Span semantic conventions are implemented. Supported opt-in attributes can be configured using the opt_in_attrs option.

Options

Opt-in Semantic Convention Attributes

Otel SemConv requires users to explicitly opt in for any attribute with a requirement level of opt-in. To ensure compatability, always use the SemConv attribute.

Example:

OptInAttrs = [{?HTTP_REQUEST_BODY_SIZE, true}]`
opentelemetry_cowboy:setup(#{opt_in_attrs => OptInAttrs)

Request and Response Headers as Opt-in Attributes

Request and response header attributes are opt-in and can be set with the request_headers and response_headers options. Values should be lower-case.

opentelemetry_cowboy:setup(#{request_headers => ["x-customer-id"]})

Public Endpoint

Setting an endpoint as public will result in any propagated trace to be added as a link, rather than a continuation of an existing trace. The public_endpoint option should be set to true if an endpoint only accepts public traffic to prevent missing root spans. By default, the endpoint is handled as non-public, resulting in traces being continued rather than linked.

In a mixed traffic environment, an MFA can be supplied to determine whether to treat a request as public. This function is executed on every request, so refrain from expensive operations such as lookups to external systems. The function must be a predicate function of arity-2, accepting the Req from the request as the first argument and user-supplied options as the second. Any dynamic information used in comparisons should be supplied at setup time for efficiency.

Example:

-module(public_endpoint).

is_public_request(Req, Opts) ->
    # return true if request was public

opentelemetry_cowboy:setup(#{public_endpoint_fn => {public_endpoint, fun is_public_request/2, []}}).