HotROD is a demo “ride sharing” application written in Golang. This is a demo application that consists of several microservices and illustrates the use of the OpenTracing API.

Start App

Start the app as a Docker Container with the following command:

docker run --rm -it \ --link jaeger -p8080-8083:8080-8083 \ jaegertracing/example-hotrod:1.3 \ --jaeger-agent.host-port=jaeger:6831

More details on the sample application can be found at https://github.com/jaegertracing/jaeger/tree/master/examples/hotrod

With HotROD started, view the application at https://[[HOST_SUBDOMAIN]]-8080-[[KATACODA_HOST]].environments.katacoda.com/

Within the application, by clicking one of the four buttons we summon a car to arrive to the customer’s location, perhaps to pick up a product and deliver it elsewhere. Once a request for a car is sent to the backend, it responds with the car’s license plate number and the expected time of arrival.

There are a few bits of debugging information we see on the screen.

1) In the top left corner there is a web client id: 9323. It is a random session ID assigned by Javascript UI; if we reload the page we get a different session ID.

2) In the line about the car we see a request ID req: 9323–1. It is a unique ID assigned by Javascript UI to each request it makes to the backend, composed of the session ID and a sequence number.

3) The last bit of debugging data, latency: 782ms, is measured by the Javascript UI and shows how long the backend took to respond.

This additional information has no impact on the behavior of the application, but will be useful when we look under the hood.

With cars requested by the application, tracing output will have been generated and stored within Jaeger.

View the Jaeger dashboard at https://[[HOST_SUBDOMAIN]]-16686-[[KATACODA_HOST]].environments.katacoda.com/

Under the Find Traces caption, the Services dropdown contains the names of the services we saw in the dependency diagram.

The frontend is the root service, choose this from the list and select Find Traces.

The system found one trace and displayed some meta-data about it, such as the names of different services that participated in the trace, and the number of spans each service emitted to Jaeger. The top level endpoint name is displayed in the title bar: HTTP GET /dispatch.

In the next step we'll explain the timeline view.

The timeline view shows a typical view of a trace as a time sequence of nested spans, where a span represents a unit of work within a single service. The top level span, also called the root span, represents the main HTTP request from Javascript UI to the frontend service, which in turn called customer service, which in turn called a MySQL database.