Cross application tracing

Important

A distributed tracing feature is now available. Distributed tracing improves on cross application tracing and is recommended for monitoring activity in complex distributed systems.

Cross application tracing is supported by the Python agent through built in instrumentation and through the use of APIs for custom instrumentation.

The protocol used to communicate between applications involves attaching metadata to requests and responses. The metadata is processed by each application and the resulting data is reported by the agent.

Requirements

You must have Python agent version 2.92.0.78 or higher.

Custom client (HTTP)

These APIs are used for custom HTTP communication libraries that are not instrumented as part of the built in instrumentation.

HTTP cross application tracing uses HTTP headers to transport transaction metadata across applications. To generate outbound cross application tracing headers, use the generate_request_headers API on the ExternalTrace class. To process inbound cross application tracing headers, use the process_response_headers API on the ExternalTrace class.

import newrelic.agent
transaction = newrelic.agent.current_transaction()
# returns a list of tuples in the form (header_name, header_value)
outgoing_headers = newrelic.agent.ExternalTrace.generate_request_headers(transaction)
for header_name, header_value in outgoing_headers:
    ...request.putheader(header_name, header_value) # code to be instrumented
...make_request(request) # code to be instrumented

import newrelic.agent
transaction = newrelic.agent.current_transaction()
trace = newrelic.agent.ExternalTrace(transaction, 'library', 'http://example.com', 'get')
with trace:
    response = fetch_example_dot_com() # code to be instrumented
    trace.process_response_headers(...response.headers)

Custom client (non-HTTP)

These APIs are used to instrument libraries that do not use the HTTP transport (and therefore may not be able to use headers as a metadata transport) and are not instrumented as part of the built in instrumentation.

Example Instrumentation

import newrelic.agent
transaction = newrelic.agent.current_transaction()
# returns a string value
outgoing_metadata = newrelic.agent.ExternalTrace.get_request_metadata(transaction)
...request.add_metadata(outgoing_metadata) # code to be instrumented
...make_request(request) # code to be instrumented

import newrelic.agent
transaction = newrelic.agent.current_transaction()
trace = newrelic.agent.ExternalTrace(transaction, 'library', 'myproto://service', 'fetch')
with trace:
    ...response = fetch_from_service() # code to be instrumented
    # extract the metadata string sent from the service
    metadata_value = response.metadata # code to be instrumented
    trace.process_response_metadata(metadata_value)

WSGI server

Tip

The agent will automatically handle processing and sending responses to cross application trace metadata for all WSGI servers.

For information on instrumenting WSGI servers, see the wsgi_application API documentation for details.

Custom non-HTTP server

Custom servers that are not WSGI based or do not use HTTP as a transport will have to process incoming cross application tracing metadata and generate cross application trace responses.

The following APIs allow processing of cross application tracing metadata sent on non-HTTP requests and generating response metadata to send back to the caller.

import newrelic.agent
def handle_incoming_request(request):
    transaction = newrelic.agent.current_transaction()
    if transaction:
        transaction.process_request_metadata(...request.metadata)
    response = generate_response() # code to be instrumented
    if transaction:
        # get_response_metadata returns a string
        ...response.metadata = transaction.get_response_metadata()
    return response

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Important

Requirements

Custom client (HTTP)

Outgoing requests

Incoming response

Custom client (non-HTTP)

Example Instrumentation

Outgoing requests

Incoming response

WSGI server

Tip

Custom non-HTTP server

Example instrumentation

For more help

Cross application tracing

Important

Requirements

Custom client (HTTP)

Incoming response

Custom client (non-HTTP)

Example Instrumentation

Outgoing requests

Incoming response

WSGI server

Tip

Custom non-HTTP server

Example instrumentation

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For more help