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+# Hot R.O.D. - Rides on Demand
+
+This is a demo application that consists of several microservices and illustrates
+the use of the OpenTelemetry API & SDK. It can be run standalone, but requires Jaeger backend
+to view the traces. A tutorial / walkthrough is available:
+  * as a blog post [Take Jaeger for a HotROD ride][hotrod-tutorial],
+  * as a video [OpenShift Commons Briefing: Distributed Tracing with Jaeger & Prometheus on Kubernetes][hotrod-openshift].
+
+As of Jaeger v1.42.0 this application was upgraded to use the OpenTelemetry SDK for traces.
+
+## Features
+
+* Discover architecture of the whole system via data-driven dependency diagram
+* View request timeline & errors, understand how the app works
+* Find sources of latency, lack of concurrency
+* Highly contextualized logging
+* Use baggage propagation to
+  * Diagnose inter-request contention (queueing)
+  * Attribute time spent in a service
+* Use [opentelemetry-go-contrib](https://github.com/open-telemetry/opentelemetry-go-contrib) open source libraries to instrument HTTP and gRPC requests with minimal code changes
+
+## Running
+
+### Run everything via `docker-compose`
+
+* Download `docker-compose.yml` from https://github.com/jaegertracing/jaeger/blob/main/examples/hotrod/docker-compose.yml
+* Optional: find the latest Jaeger version (see https://www.jaegertracing.io/download/) and pass it via environment variable `JAEGER_VERSION`. Otherwise `docker compose` will use the `latest` tag, which is fine for the first time you download the images, but once they are in your local registry the `latest` tag is never updated and you may be running stale (and possibly incompatible) verions of Jaeger and the HotROD app.
+* Run Jaeger backend and HotROD demo, e.g.:
+  * `JAEGER_VERSION=1.52 docker-compose -f path-to-yml-file up`
+* Access Jaeger UI at http://localhost:16686 and HotROD app at http://localhost:8080
+* Shutdown / cleanup with `docker-compose -f path-to-yml-file down`
+
+Alternatively, you can run each component separately as described below.
+
+### Run everything in Kubernetes
+
+```bash
+kustomize build ./kubernetes | kubectl apply -f -
+kubectl port-forward -n example-hotrod service/example-hotrod 8080:frontend
+# In another terminal
+kubectl port-forward -n example-hotrod service/jaeger 16686:frontend
+
+# To cleanup
+kustomize build ./kubernetes | kubectl delete -f -
+```
+
+Access Jaeger UI at http://localhost:16686 and HotROD app at http://localhost:8080
+
+### Run Jaeger backend
+
+An all-in-one Jaeger backend is packaged as a Docker container with in-memory storage.
+
+```bash
+docker run \
+  --rm \
+  --name jaeger \
+  -p6831:6831/udp \
+  -p16686:16686 \
+  -p14268:14268 \
+  jaegertracing/all-in-one:latest
+```
+
+Jaeger UI can be accessed at http://localhost:16686.
+
+### Run HotROD from source
+
+```bash
+git clone git@github.com:jaegertracing/jaeger.git jaeger
+cd jaeger
+go run ./examples/hotrod/main.go all
+```
+
+### Run HotROD from docker
+```bash
+docker run \
+  --rm \
+  --link jaeger \
+  --env OTEL_EXPORTER_JAEGER_ENDPOINT=http://jaeger:14268/api/traces \
+  -p8080-8083:8080-8083 \
+  jaegertracing/example-hotrod:latest \
+  all
+```
+
+Then open http://127.0.0.1:8080
+
+## Metrics
+
+The app exposes metrics in either Go's `expvar` format (by default) or in Prometheus format (enabled via `-m prometheus` flag).
+  * `expvar`: `curl http://127.0.0.1:8083/debug/vars`
+  * Prometheus: `curl http://127.0.0.1:8083/metrics`
+
+## Linking to traces
+
+The HotROD UI can generate links to the Jaeger UI to find traces corresponding
+to each executed request. By default it uses the standard Jaeger UI address
+http://localhost:16686, but if your Jaeger UI is running at a different address,
+it can be customized via `-j <address>` flag passed to HotROD, e.g.
+
+```
+go run ./examples/hotrod/main.go all -j http://jaeger-ui:16686
+```
+
+[hotrod-tutorial]: https://medium.com/jaegertracing/take-jaeger-for-a-hotrod-ride-233cf43e46c2
+[hotrod-openshift]: https://blog.openshift.com/openshift-commons-briefing-82-distributed-tracing-with-jaeger-prometheus-on-kubernetes/