ab-example

Use Case

Suppose we have a two tier application. The business logic (frontend) provides a customer facing application that recommends products to a user. The user can then buy a recommended product if desired. The frontend relies on a backend recommendation service. Given a set of options for the backend recommendation service, we would like to evaluate them to determine which gives us the greatest business benefit; for example, the greatest number of sales.

Note that the benefit of a backend cannot be determined in isolation from the frontend. The benefit comes from the results of (perhaps multiple) recommendations and can be determined only by the frontend service.

To address the challenge of associating a business metric computed by a frontend service with a backend service is addressed by the introduction of the Iter8 SDK and ABn service. The SDK, to be used to implement frontend services, provides two APIs:

• lookup() - identifies a version of the backend service that should be used for a request
• writeMetric() - exports a business metric and associated it with the associated backend service

Application

This project contains a sample two-tier application that demonstrates the use of the Iter8 SDK by the frontend service.

The frontend service provides two endpoints /getRecommendation and /buy. The /getRecommendation endpoint relies on a backend service endpoint /recommend:

To compare multiple versions of the backend service, use the Iter8 SDK to identify which version or track of the backend to send a request to and to export metrics to a metrics data:

An Iter8 experiment can then be written to evaluate the versions.

Sample implementations of the frontend service in go, python and node demonstrate the use of the Iter8 API. These are simplified code examples.

Prerequisite

A Kubernetes cluster with ABn service deployed:

helm install abn ../../iter8-tools/iter8/charts/abn-service-single/ \
--set image=$ABN_SERVICE_TAG \
--set resources='{deployments,services}' \
--set service.name=abn \
--set application=backend

Backend Service

Build:

docker build . -f backend/Dockerfile -t $BACKEND_TAG
docker push $BACKEND_TAG

Deploy two versions of the backend service. One, v1 is identified as the default version. The other, v2 is the candidate version. While the specific versions will change over time, we always evaluate a candidate version against a default version.

sed -e "s#BACKEND_TAG#$BACKEND_TAG#" backend/deploy.yaml | kubectl apply -f -

Comments:

In order to implement a lookup service, the Iter8 ABn service needs to be able to identify available versions of the backend service and be able to identify them as belonging either to the default or candidate track. To do this, the ABn service relies on resource labels and annotations as follows:

• resources associated with backend service, have the label app.kubernetes.io/name: backend
• resources associated with the backend service can be partitioned into versions via the label app.kubernetes.io/version; resources without this label are ignored
• a version is identified as either default or candidate by the annotation iter8.tool/track on a resource
• a version is available if the annotation iter8.tool/ready: True is set on some resource associated with the track

In backend/deploy.yaml, these labels and annotations are defined as required.

Frontend Service

Sample implementations are provided in:

• go
• python
• node

Build

Set FRONTEND_LANG to implementation language, one of go, python or node.

Set FRONTEND_TAG to the name of a docker image. Then build as follows:

docker build . -f frontend/$FRONTEND_LANG/Dockerfile -t $FRONTEND_TAG
docker push $FRONTEND_TAG

Deploy

Deploy the frontend service:

sed -e "s#FRONTEND_TAG#$FRONTEND_TAG#" frontend/deploy.yaml | kubectl apply -f -

Test

Port forward the frontend service:

kubectl port-forward deploy/frontend 8090:8090

Call (perhaps several times):

curl localhost:8090/getRecommendation -H 'X-User: foo'

Note that the returned recommendation is, in fact, the version of the backed service used to process the request.

Then:

curl localhost:8090/buy -H 'X-User: foo'

Currently, the metric is written to the ABn service log:

kubectl logs -f deploy/abn

data:
  versionname.metricname: <base64 encoded object - count, sum, min, max, ss, lut>
  ...

// great for writing

data:
  versionname:
    metricname:
      encodedmetric: <base64 encoded object - count, sum, min, max, ss>
      lastupdatetime:
    metricname:
    ...
    lastupdatetime: <max of all lut>
  versionname:
  ...

// best for reading, removing old version data


data:
  metricname:
    versionname: <base64 encoded object - count, sum, min, max, ss, lut>
    versionname:
    ...
  metricname:
  ...

// good for writing