MEP for adding OpenTelemetry tracing to minikube

enhancements/proposed/20201030-tracing/README.md

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+# Tracing minikube
+
+* First proposed: Oct 30 2020
+* Authors: Priya Wadhwa (priyawadhwa@)
+
+## Reviewer Priorities
+
+Please review this proposal with the following priorities:
+
+*   Does this fit with minikube's [principles](https://minikube.sigs.k8s.io/docs/concepts/principles/)?
+*   Are there other approaches to consider?
+*   Could the implementation be made simpler?
+*   Are there usability, reliability, or technical debt concerns?
+
+Please leave the above text in your proposal as instructions to the reader.
+
+## Summary
+
+This proposal covers using the [OpenTelemetry](https://github.com/open-telemetry/opentelemetry-go) API to provide tracing data for minikube.
+This data would be useful for maintainers to identify areas for performance improvements.
+This data would also be used to create a dashboard of current performance and would allow us to catch performance regressions more quickly.
+
+## Goals
+
+*   Trace data is can be collected and exported for `minikube start`
+*   `minikube start` can either create a new Trace or can read from a file and append data to an existing Trace
+*   It is easy for users to add their own exporters if they wish to export data to their own service
+*   We are able to create dashboards around `minikube start` performance that will alert maintainers if regressions happen
+
+## Non-Goals
+
+*   Collecting trace data for the minikube cluster while it is running
+
+## Design Details
+
+There are two pieces to the design: collecting the data and exporting the data.
+
+### Collecting Data
+Luckily, we already have a lot of this infrastructure set up for JSON output.
+We know when a new substep of `minikube start` has started, because we call it explictly via `register.SetStep`.
+We also know that substep has ended when a new substep begins.
+
+We can start new spans whenever `register.SetStep` is called, and thus collect tracing data.
+
+### Exporting Data
+OpenTelemetry supports a variety of [user-contributed exporters](https://github.com/open-telemetry/opentelemetry-go-contrib/tree/master/instrumentation).
+It would be a lot of work to implement all of them ourselves.
+
+Instead, I propose writing a simple `GetExporter` function that would return whatever exporter is requested via a `--trace` flag.
+
+So, something like this would tell minikube to use the `stackdriver` exporter:
+
+```
+minikube start --trace=stackdriver
+```
+
+Users can then contribute to minikube if they need to use an exporter that isn't currently provided.
+
+Exporters also will require additional information to make sure data is sent to the correct place.
+This could include things like, but not limited to:
+* project ID
+* zone
+
+Since it could get messy passing in these things as flags to `minikube start`, I propose that these values are set via environment variable.
+All environment variables will be of the form:
+
+```
+MINIKUBE_TRACE_PROJECT_ID
+```
+and the user-contributed code is responsible for parsing the environment variables correctly and returning the exporter.
+
+### Testing Plan
+
+I will set up a dashboard and alerting system in the minikube GCP project.
+If we are collecting data at a consistent rate, and the dashboard is populated, we will know that this has worked.
+
+
+## Alternatives Considered
+
+### Building a Wrapper Binary
+A wrapper binary could run `minikube start --output json` and collect the same data, and then export it to whatever service we need.
+
+A large advantage of this is that the minikube code doesn't have to be changed at all for this to work.
+
+However, I decided against this in case other tools that consume minikube or users want to collect this data as well -- it is much easier to pass in a flag to minikube than to download another binary.