Continuing this short series of writing a simple echo service web API along with the docker and k8s requirements, we’re now going to turn our attention to a Elixir implementation.

Implementation

I’m going to be using Visual Code and dev containers, so I created a folder echo_service which has a folder named .devcontainer with the following devcontainer.json

{
    "image": "elixir",
    "forwardPorts": [3000]
}

Next I opened Visual Code in the echo_service folder and it should detect the devtonainer and ask if you want to reopen in the devcontainer. To which we do.

I’m going to use Phoenix Server (phx), so I open the terminal in Visual Code and run the following

• I needed to install phx installer, using

  mix archive.install hex phx_new
  

• Next I want to generate a minimal phx server, hence run the following

  mix phx.new echo_service --no-html --no-ecto --no-mailer --no-dashboard --no-assets --no-gettext
  

  When this prompt appears, type y

  Fetch and install dependencies? [Yn]
  

• Now cd into the newly created echo_service folder
• To check everything is working, run

  mix phx.server
  

Next we need to add a couple of controllers (well we could just use one but I’m going to create a Echo controller and a Health controller). So in lib/echo_service_web/controllers add the files echo_controller.ex and health_controller.ex

The echo_controller.ex looks like this

defmodule EchoServiceWeb.EchoController do
  use Phoenix.Controller, formats: [:html, :json]

  def index(conn, %{"text" => text}) do
    send_resp(conn, 200, "Elixir Echo: #{text}")
  end
end

The health_controller.exe should look like this

defmodule EchoServiceWeb.HealthController do
  use Phoenix.Controller, formats: [:html, :json]

  def livez(conn, _params) do
    send_resp(conn, 200, "Live")
  end

  def readyz(conn, _params) do
    send_resp(conn, 200, "Ready")
  end
end

In the parent folder (i.e. lib/echo_service_web) edit the router.exe so it looks like this

defmodule EchoServiceWeb.Router do
  use EchoServiceWeb, :router

  pipeline :api do
    plug :accepts, ["json"]
  end

  scope "/", EchoServiceWeb do
    # pipe_through :api
    get "/echo", EchoController, :index
    get "/livez", HealthController, :livez
    get "/readyz", HealthController, :readyz
  end
end

Now we can run mix phx.server again (ctrl+c twice to shut any existing running instance).

Dockerfile

Next up we need to create our Dockerfile

FROM elixir:latest

RUN mkdir /app
COPY . /app
WORKDIR /app

RUN mix local.hex --force
RUN mix do compile

ENV PORT=8080
EXPOSE 8080

CMD ["mix", "phx.server"]

Note: In Linux port 80 might be locked down, hence we use port 8080 – to override the default port in phx we also set the environment variable PORT.

To build this, run

docker build -t putridparrot.echo_service:v1 .

Don’t forget to change the name to your preferred name.

To test this, run

docker run -p 8080:8080 putridparrot.echo_service:v1

Kubernetes

If all wen well we’ve not tested our application and see it working from a docker image, so now we need to create the deployment etc. for Kubernete’s. Let’s assume you’ve pushed you image to Docker or another container registry such as Azure – I’m call my container registry putridparrotreg.

I’m also not going to use helm at this point as I just want a (relatively) simple yaml file to run from kubectl, so create a deployment.yaml file, we’ll store all the configurations, deployment, service and ingress in this one file jus for simplicity.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: echo
  namespace: dev
  labels:
    app: echo
spec:
  replicas: 1
  selector:
    matchLabels:
      app: echo
  template:
    metadata:
      labels:
        app: echo
    spec:
      containers:
      - name: echo
        image: putridparrotreg/putridparrot.echo_service:v1
        ports:
        - containerPort: 8080
        resources:
          requests:
            memory: "100Mi"
            cpu: "100m"
          limits:
            memory: "200Mi"
            cpu: "200m"
        livenessProbe:
          httpGet:
            path: /livez
            port: 8080
          initialDelaySeconds: 30
          periodSeconds: 10
        readinessProbe:
          httpGet:
            path: /readyz
            port: 8080
          initialDelaySeconds: 5
          periodSeconds: 5

---
apiVersion: v1
kind: Service
metadata:
  name: echo_service
  namespace: dev
  labels:
    app: echo
spec:
  type: ClusterIP
  selector:
    app: echo 
  ports:
  - name: http
    port: 80
    targetPort: 8080
    protocol: TCP
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: echo-ingress
  namespace: dev
  annotations:
    kubernetes.io/ingress.class: "nginx"
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  rules:
  - host: mydomain.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: echo_service
            port:
              number: 80

Don’t forget to change the “host” and image to suit, also this assume you created a namespace “dev” for your app. See Creating a local container registry for information on setting up your own container registry.