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Cow Demo Application

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Cow Demo is a nice web application, written in Go, used for demonstrating Kubernetes and load balancing.

💡 This is a hard fork of oskapt/rancher-demo who hasn't been updated since 2021. It also took the updates from bashofmann/rancher-demo.

Presentation

It will create a colored icon for each replica within a ReplicaSet and indicate which one most recently served a response. Replicas which haven't been heard from will begin to fade out, until after a configurable number of seconds they will disappear. This is useful for demonstrating scaling up/down an upgraded application.

Quickstart with a container

If you have a container engine running, you can start right away with the image:

docker run --rm -p 8080:8080 ghcr.io/suse/cow-demo

Open the web application and enjoy the interactive display!

Deploy in an environment

The recommanded way to run the application is to deploy in a Kubernetes cluster with with the Helm chart.

Configuration

Environment variables:

  • TITLE: sets title in demo app
  • SHOW_VERSION: show version of app in ui (VERSION env var)
  • REFRESH_INTERVAL: interval in milliseconds for page to refresh (default: 1000)
  • EXPIRE_INTERVAL: how long a replica can go without being seen before we remove it from the display (default: 10s)
  • REMOVE_INTERVAL: how long after EXPIRE_INTERVAL until we remove the icon (default: 20s)
  • SKIP_ERRORS: set this to prevent errors from counting
  • METADATA: extra text at bottom of info area
  • CONTAINER_COLOR: what color the container background should be (default: black). Valid options are any color from the CSS pallet, including:
    • red
    • orange
    • yellow
    • olive
    • green
    • teal
    • blue
    • violet
    • purple
    • pink
    • black
  • PETS: The kind of pet shown in each container. Valid options are:
    • cows
    • chameleons
    • cowmeleons

Local development

How to test

Run in a terminal:

go test -v ./...

How to run locally

Update the dependencies (if a change has been made):

go mod tidy

Build the application:

go build

Build web content files (not working for the moment):

cd ui && npm install
cp -f semantic.theme.config semantic/src/theme.config && mkdir -p semantic/src/themes/app && cp -rf semantic.theme/* semantic/src/themes/app
cd semantic && npx gulp build
mkdir -p ../../static/dist/themes/default/ && cp -f dist/semantic.min.css ../../static/dist/semantic.min.css && cp -f dist/semantic.min.js ../../static/dist/semantic.min.js && cp -r dist/themes/default/assets ../../static/dist/themes/default/
cd ../..

Start the web server:

PETS=chameleons CONTAINER_COLOR=purple ./cow-demo

Open localhost:8080

How to run in a container

The container image is using SUSE BCI (Base Container Images).

Build a local image:

docker build -t cow-demo .

Start a container:

docker run --rm -p 8080:8080 -e COW_COLOR:purple cow-demo

Open localhost:8080

Paths

By default the loaded page will reach back to /demo every REFRESH_INTERVAL and use the returned information to update the display. Other paths are:

  • /info - returns some additional information about the replica serving the request
  • /load - adds a 2s delay to the response from /info - use this for putting artificial load on the system and watching the replicas scale

Backlog

  • Upgrade semantic-ui ("2.2.13") to 2.4 and make dist folder creation works (to be removed from git)
  • Publish arm and arm64 container images

Dependencies

This application is using urfave/cli and semantic-ui.