add tep for jaeger tracing

Signed-off-by: Jayadeep KM <kmjayadeep@gmail.com>

teps/0124-distributed-tracing-for-tasks-and-pipelines.md

@@ -0,0 +1,72 @@
+---
+status: proposed
+title: Distributed tracing for Tasks and Pipelines
+creation-date: '2022-09-30'
+last-updated: '2022-09-30'
+authors:
+- '@kmjayadeep'
+---
+
+# TEP-0124: Distributed tracing for Tasks and Pipelines
+
+<!-- toc -->
+- [Summary](#summary)
+  - [Goals](#goals)
+  - [Non-Goals](#non-goals)
+  - [Use Cases](#use-cases)
+- [Proposal](#proposal)
+  - [PipelineRun controller](#pipelinerun-controller)
+  - [TaskRun controller](#taskrun-controller)
+  - [Test Plan](#test-plan)
+<!-- /toc -->
+
+## Summary
+
+With distributed tracing, we can track the time taken by each action in the pipeline like reconciling logic, fetching resources, pulling images etc.
+This allows the developers to improve the reconciliation logic and also allow end users to monitor and optimize the pipelines.
+
+### Goals
+
+* Implementation of opentelemetry tracing with Jaeger
+* Instrumentation of pipelinerun and taskrun reconciliation logic
+* Able to visualize pipeline and task reconciliation steps in jaeger
+
+### Non-Goals
+
+* Instrumentation of sidecars and initcontainers
+* Support for more tracing backends
+* Instrumentation of individual steps in each task
+* Adding events to each span to indicate what is happening inside each
+  method. This is an improvement task, and it can be done later once the
+  basic setup for tracing is in place. The scope of this proposal is
+  only to get the plumbing done by covering only the method boundaries.
+
+### Use Cases
+
+Pipeline and Task User:
+* I would like to understand the duration of each task in my pipeline so that I can optimize the slow taks to improve the pipeline execution speed
+
+Tekton Developer:
+* I would like to understand the duration of each reconciliation step, so that I can optimize the code to improve reconciliation performance
+* When the pipelines are failing due to a bug, I would like to understand which reconciliation logic caused the issue so that I can easily fix the problem
+
+## Proposal
+
+Initialize a tracer provider with jaeger as the backend for each reconciler. The jaeger collector URL can be passed as an argument to the controller.
+
+### PipelineRun controller
+A new trace will be initialized in the pipelineRun controller when a new PipelineRun CR is created. The span context will be propogated through the reconciliation methods
+to instrument the actions and steps included in the reconciliation logic. The span context will be saved back to the PipelineRun CR as an annotation `tekton/pipelinerun-span-context`. This span context can
+be retrieved during the next reconciliation loop for the same CR. This way, we will have a single parent span for the entire reconciliation logic for a single PipelineRun CR. This makes it easy to visualize
+the multiple reconciliation steps involved for each PipelineRun.
+
+When a TaskRun is created by the PipelineRun reconciler, the parent span context is passed as an annotation `tekton/taskrun-span-context` so that TaskRun reconciler use the same span as its parent.
+
+### TaskRun controller
+TaskRun reconciler retrieves the parent span context propogated by PipelineRun controller. If it is not present (TaskRun is created by user in this case), a new span will be created. It will be used to 
+instrument the logic similar to PipelineRun controller.
+The spancontext should be also made available as environment variables containers (using downward api) running the tasks. So that the task containers can continue the span if it supports it.
+
+### Test Plan
+
+There must be unit tests for recording of spans and e2e tests for context propogation through custom resources. 

teps/README.md

@@ -286,3 +286,4 @@ This is the complete list of Tekton teps:
 |[TEP-0118](0118-matrix-with-explicit-combinations-of-parameters.md) | Matrix with Explicit Combinations of Parameters | implementable | 2022-08-08 |
 |[TEP-0119](0119-add-taskrun-template-in-pipelinerun.md) | Add taskRun template in PipelineRun | implementable | 2022-09-01 |
 |[TEP-0120](0120-canceling-concurrent-pipelineruns.md) | Canceling Concurrent PipelineRuns | proposed | 2022-08-19 |
+|[TEP-0124](0124-distributed-tracing-for-tasks-and-pipelines.md) | Distributed tracing for Tasks and Pipelines | proposed | 2022-09-30 |