Web server with Redis

Demo running a simple web server backed by Redis on kind

With Imageless Kubernetes, you can run a container just like in any other Kubernetes deployment, but you don’t have to build a container image.

To demonstrate this, we’ll run a simple web server backed by Redis using two Flox environments.

Running the example

The entirety of this example can be run locally with the following commands:

git clone https://github.com/flox/flox-kind-demo.git &&
cd flox-kind-demo &&
flox activate -- just up

This starts a local Kubernetes cluster using kind and deploys a web server backed by Redis.

To fetch something from the web server, run:

curl localhost:3000/quotes/0

Quotes app environment

The example runs a deployment of flox/quotes-app, which is just like any other Kubernetes deployment, but with a few key differences. Here’s a snippet from the deployment manifest:

metadata:
  labels:
    app: quotes
  annotations:
    flox.dev/environment: "flox/quotes-app"
spec:
  runtimeClassName: flox
  containers:
    - name: quotes
      image: flox/empty:1.0.0
      command: ["quotes-app-go", "-r", "redis:6379"]

The full deployment manifest can be found in the flox-kind-demo repo.

There are two key lines needed to run the container using a Flox environment instead of a container image:

• Specifying runtimeClassName: flox runs the container using the Flox containerd shim.
• The annotation flox.dev/environment: "flox/quotes-app" specifies the Flox environment to use to bootstrap the container filesystem instead of a container image

Just as with any container, you can specify a startup command, which is ["quotes-app-go", "-r", "redis:6379"] in this case.

When the container starts, the flox/quotes-app Flox environment is pulled from FloxHub and bind mounted into the container. This environment contains the flox/quotes-app-go package, which is a simple web server published to FloxHub. When the container starts, the environment is activated, and then quotes-app-go is run inside the activated environment.

Redis environment

The quotes-app-go server uses a Redis instance running in a second deployment. Just like the first pod, rather than specifying a container image, the Redis deployment runs the environment flox/redis which is pulled from hub.flox.dev/flox/redis.

Here’s the relevant snippet from the Redis deployment manifest:

metadata:
  labels:
    app: redis
  annotations:
    flox.dev/environment: "flox/redis"
spec:
  runtimeClassName: flox
  containers:
    - name: redis
      image: flox/empty:1.0.0
      command: ["redis-server", "--daemonize", "no", "--dir", "/data", "--bind", "0.0.0.0", "--protected-mode", "no" ]
      volumeMounts:
        - name: redis-data
          mountPath: /data

The full deployment manifest can be found in the flox-kind-demo repo.

Updating the deployment

Because the environment is hosted on FloxHub, there’s no need to rebuild a container image to update the deployment. After a change to quotes-app-go, updating the deployment would require running a flox publish for quotes-app-go and a flox upgrade -r flox/quotes-app. After that, restarting a pod will pull the latest generation of the environment. This allows deploying software with the reproducibility of a container, but without the overhead of having to rebuild an entire container image when iterating.

Cleaning up

To tear down the local kind cluster, run:

just down