diff-web

A proxy to A/B test web services.

A common pattern to test web services is to deploy a copy of the server with the new code under a different host/ELB while the baseline/control instance is left untouched. During this time, various manual and automated tests are run to ensure the new instance of the service meets QA acceptance.

While some changes are expected (addition of new fields, removal of deprecated ones), most day to day bug fixes and under the hood improvements are not expected to change the final output of the service. diff-web is a proxy that forwards your requests to 2 endpoints before diff-ing the response body.

Installation

NOTE: We require the diff command to be available in the $PATH.

Build from source

Get stack

Clone this repository

git clone git@github.com:naushadh/diff-web.git

From repository folder, build

stack build --pedantic --ghc-options '-O2'

Install
```
stack install diff-web-exe
```

Usage

Settings

The following settings can be set via ENV

DIFF_PORT=8080

Launch

$ diff-web-exe
... should print port listened on

Proxy requests

Send all desired requests to the app
Ensure the following headers are set for forward endpoints
```
DIFF_HOST_A: app.com
DIFF_HOST_B: dev.app.com
```
When responses are the same, you get the response from host B
When responses differ, you get a 400 error with the diff in the body.

TODO

In no particular order

Add a simple HTML UI for better user-friendliness (esp: very large diffs).
Add tests
Add Dockerfile for build+deployment convenience
Find a pure haskell diff alternative and/or ship it with the app to ensure we're fully self contained.