Service Preview

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How do you verify that the code you've written actually works? Ambassador's Service Preview lets developers see exactly how their service works in a realistic environment -- without impacting other developers or end-users. Service Preview integrates Telepresence, the popular CNCF project for local development and debugging on Kubernetes.

Install apictl

apictl is the command client for Ambassador.

Download the latest version of the client:

Mac 64-bit |Linux 64-bit

Make sure the client is somewhere on your PATH. In addition, place your license key in ~/.ambassador.key.

Information about open-source code used in apictl can be found by running apictl --version.

Getting Started

In this quick start, we're going to preview a change we make to the backend service of the quote application, without impacting normal users of the application. Before getting started, make sure the quote application is installed on your cluster and you've installed the apictl command-line tool, as explained above.

  1. We're first going to get the quote backend service running locally. Clone the quote repository and build a local image.

    git clone
    cd quote

    Note that Preview doesn't depend on a locally running container; you can just run a service locally on your laptop. We're using a container in this tutorial to minimize environmental issues with different Golang environments.

    In the make command above, we build the backend application in a docker container named localhost:31000/quote:backend-latest and run it on port 8080.

  2. Now, in another terminal window, redeploy the quote application with the Preview sidecar. The sidecar is a special process that will route requests to your local machine or the production cluster. The apictl traffic inject command will automatically create the appropriate YAML to inject the sidecar. In the quote directory, pass the file name of the QOTM deployment:

    apictl traffic inject k8s/tour.yaml -d tour -s tour -p 8080 > k8s/tour-traffic-sidecar.yaml

    This will create a YAML file called qotm-sidecar.yaml. The file will look like the following:

    kind: Mapping
    name: quote-backend
    prefix: /backend/
    service: quote:8080
    - request_label:
    - backend
    apiVersion: v1
    kind: Service
    name: quote
    - name: backend
    port: 8080
    targetPort: 9900
    app: quote
    apiVersion: apps/v1
    kind: Deployment
    name: quote
    replicas: 1
    app: quote
    type: RollingUpdate
    app: quote
    - image:
    name: quote
    - containerPort: 8080
    name: http
    cpu: "0.1"
    memory: 100Mi
    - env:
    - name: APPNAME
    value: quote
    - name: APPPORT
    value: "8080"
    value: eJcbGciOiaIUzI1NiIsInR5cCkpXVCJ9.eCI6Im5rcmF1c2UiLCJleHAiOjE1Nzg0MTg4ODZ9.S_6-zdPyy4z1N4Jmo5e4A7fME4CbQVL_13ikw
    name: traffic-sidecar
    - containerPort: 9900

    If you examine this file, you will notice a couple of important difference:

    • The traffic-sidecar container has been added to the deployment
    • In the service, targetPort for the backend port mapping has been changed to point to port 9900 which is the port the traffic-sidecar container is listening on
  3. Redeploy quote with the sidecar:

    kubectl apply -f k8s/quote-traffic-sidecar.yaml
  4. Test to make sure that both your production and development instances of QOTM work:

    curl $AMBASSADOR_IP/backend/ # test production
    curl localhost:8080/ # test development
  5. Initialize the traffic manager for the cluster.

    apictl traffic initialize
  6. We need to create an intercept rule that tells Ambassador where to route specific requests. The following command will tell Ambassador to route any traffic for the quote deployment where the header x-service-preview is dev to go to port 8080 on localhost:

    apictl traffic intercept quote -n x-service-preview -m dev -t 8080
  7. Requests with the header x-service-preview: dev will now get routed locally:

    curl -H "x-service-preview: dev" $AMBASSADOR_IP/backend/` # will go to local Docker instance
    curl $AMBASSADOR_IP/backend/ # will go to production instance
  8. Make a change to the backend source code. In backend/main.go, uncomment out line 85, and comment out line 84, so it reads like so:

    //quote := s.random.RandomSelectionFromStringSlice(s.quotes)
    quote := "Service Preview Rocks!"

    This will ensure that the backend service will return a quote of "Service Preview rocks" every time.

  9. Rebuild the docker container and rerun the curl above, which will now route to your (modified) local copy of the QOTM service:

    make -C backend/
    curl -H "x-service-preview: dev" $AMBASSADOR_IP/qotm/` # will go to local Docker instance

    To recap: With Preview, we can now see test and visualize changes to our service that we've made locally, without impacting other users of the stable version of that service.

Using Service Preview

Service Preview will match HTTP headers based on the headers that are seen by the sidecar and not the edge gateway. Matches are made on the whole header, e.g., a match rule of dev will not match in the example above, while /backend/dev will match.

While any HTTP header will match, in practice, using host-based routing (i.e., the :authority header), a custom HTTP header (e.g., the x-service-preview header used above), or an authentication header is recommended.