JAEGER- DISTRIBUTED TRACING
===========================

Jaeger provides ready-to-use tracing services for distributed systems. 

BASIC ARCHITECTURE AND TERMINOLOGY
----------------------------------

* TRACE: A trace shows the data/execution path through a system.
* SPAN: A single unit of a trace. A data structure that stores information such
  as the operation name, timestamps, and the ordering within a trace.
* JAEGER CLIENT: Language-specific implementations of the OpenTracing API.
* JAEGER AGENT: A daemon that listens for spans sent over User Datagram
  Protocol. The agent is meant to be placed on the same host as the
  instrumented application. (The Jaeger agent acts like a sidecar listener.)
* JAEGER COLLECTOR: A daemon that receives spans sent by the Jaeger agent. The
  Jaeger collector then stitches the spans together to form a trace. (A databse
  can be enabled to persist a database for these traces).
* JAEGER QUERY AND CONSOLE FRONTEND: The UI-based frontend that presents
  reports of the jaeger traces. Accessible at  http://<jaeger frontend host>:16686.

Read more about jaeger tracing:.

  https://www.jaegertracing.io/docs/

JAEGER DEPLOYMENT
-----------------

Jaeger can be deployed using cephadm, and Jaeger can be deployed manually.

Refer to one of the following:

`Cephadm Jaeger Services Deployment <../cephadm/services/tracing/>`_

`Jaeger Deployment <https://www.jaegertracing.io/docs/1.25/deployment/>`_

`Jaeger Performance Tuning <https://www.jaegertracing.io/docs/1.25/performance-tuning/>`_


Important Notes:
^^^^^^^^^^^^^^^^

- The Jaeger agent must be running on each host (and not running in all-in-one
  mode). This is because spans are sent to the local Jaeger agent. Spans of
  hosts that do not have active Jaeger agents will be lost.

- Ceph tracers are configured to send tracers to agents that listen to port
  6799. Use the option "--processor.jaeger-compact.server-host-port=6799" for
  manual Jaeger deployments. 


HOW TO ENABLE TRACING IN CEPH
-----------------------------

Tracing in Ceph is disabled by default.

Tracing can be enabled globally, and tracing can also be enabled separately for
each entity (for example, for rgw).

Enable tracing globally:

.. prompt:: bash $

   ceph config set global jaeger_tracing_enable true


Enable tracing for each entity:

.. prompt:: bash $

   ceph config set <entity> jaeger_tracing_enable true


TRACES IN RGW
-------------

Traces run on RGW can be found under the Service `rgw` in the Jaeger Frontend.

REQUESTS
^^^^^^^^
Every user request is traced. Each trace contains tags for `Operation name`,
`User id`, `Object name` and `Bucket name`.

There is also an `Upload id` tag for Multipart upload operations.

The names of request traces have the following format: `<command> <transaction
id>`.

MULTIPART UPLOAD
^^^^^^^^^^^^^^^^
There is a kind of trace that consists of a span for each request made by a
multipart upload, and it includes all `Put Object` requests.

The names of multipart traces have the following format: `multipart_upload
<upload id>`.


rgw service in Jaeger Frontend:

.. image:: ./rgw_jaeger.png
  :width: 400


osd service in Jaeger Frontend:

.. image:: ./osd_jaeger.png
  :width: 400
