Hello World - Elixir

A simple web application written in Elixir using the Phoenix Framework. The application prints all environment variables to the main page.

Set up Elixir and Phoenix Locally

Following the Phoenix Installation Guide is the best way to get your computer set up for developing, building, running, and packaging Elixir Web applications.

Running Locally

To start your Phoenix server:

  • Install dependencies with mix deps.get
  • Install Node.js dependencies with cd assets && npm install
  • Start Phoenix endpoint with mix phx.server

Now you can visit localhost:4000 from your browser.

Recreating the sample code

  1. Generate a new project.
mix phoenix.new helloelixir

When asked, if you want to Fetch and install dependencies? [Yn] select y

  1. Follow the direction in the output to change directories into start your local server with mix phoenix.server

  2. In the new directory, create a new Dockerfile for packaging your application for deployment

    # Start from a base image for elixir
# Phoenix works best on pre 1.7 at the moment.
FROM elixir:1.6.6-alpine

# Set up Elixir and Phoenix
ARG APP_NAME=hello
ARG PHOENIX_SUBDIR=.
ENV MIX_ENV=prod REPLACE_OS_VARS=true TERM=xterm
WORKDIR /opt/app

# Update nodejs, rebar, and hex.
RUN apk update \
    && apk --no-cache --update add nodejs nodejs-npm \
    && mix local.rebar --force \
    && mix local.hex --force
COPY . .

# Download and compile dependencies, then compile Web app.
RUN mix do deps.get, deps.compile, compile
RUN cd ${PHOENIX_SUBDIR}/assets \
    && npm install \
    && ./node_modules/brunch/bin/brunch build -p \
    && cd .. \
    && mix phx.digest

# Create a release version of the application
RUN mix release --env=prod --verbose \
    && mv _build/prod/rel/${APP_NAME} /opt/release \
    && mv /opt/release/bin/${APP_NAME} /opt/release/bin/start_server

# Prepare final layer
FROM alpine:latest
RUN apk update && apk --no-cache --update add bash openssl-dev ca-certificates

# Add a user so the server will run as a non-root user.
RUN addgroup -g 1000 appuser && \
    adduser -S -u 1000 -G appuser appuser
# Pre-create necessary temp directory for erlang and set permissions.
RUN mkdir -p /opt/app/var
RUN chown appuser /opt/app/var
# Run everything else as 'appuser'
USER appuser

ENV MIX_ENV=prod REPLACE_OS_VARS=true
WORKDIR /opt/app
COPY --from=0 /opt/release .
ENV RUNNER_LOG_DIR /var/log

# Command to execute the application.
CMD ["/opt/app/bin/start_server", "foreground", "boot_var=/tmp"]

  3. Create a new file, service.yaml and copy the following Service definition into the file. Make sure to replace {username} with your Docker Hub username.

    apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: helloworld-elixir
  namespace: default
spec:
  template:
    spec:
      containers:
        - image: docker.io/{username}/helloworld-elixir
          env:
            - name: TARGET
              value: "elixir Sample v1"

Building and deploying the sample

The sample in this directory is ready to build and deploy without changes. You can deploy the sample as is, or use you created version following the directions above.

  1. Generate a new secret_key_base in the config/prod.secret.exs file. Phoenix applications use a secrets file on production deployments and, by default, that file is not checked into source control. We have provides shell of an example on config/prod.secret.exs.sample and you can use the following command to generate a new prod secrets file.

    SECRET_KEY_BASE=$(elixir -e ":crypto.strong_rand_bytes(48) |> Base.encode64 |> IO.puts")
sed "s|SECRET+KEY+BASE|$SECRET_KEY_BASE|" config/prod.secret.exs.sample >config/prod.secret.exs

  2. Use Docker to build the sample code into a container. To build and push with Docker Hub, run these commands replacing {username} with your Docker Hub username:

     # Build the container on your local machine
 docker build -t {username}/helloworld-elixir .

 # Push the container to docker registry
 docker push {username}/helloworld-elixir

  3. After the build has completed and the container is pushed to docker hub, you can deploy the app into your cluster. Ensure that the container image value in service.yaml matches the container you built in the previous step. Apply the configuration using kubectl:

    kubectl apply --filename service.yaml

  4. Now that your service is created, Knative will perform the following steps:

    • Create a new immutable revision for this version of the app.
    • Network programming to create a route, ingress, service, and load balance for your app.
    • Automatically scale your pods up and down (including to zero active pods).

  5. To find the URL for your service, use

    kubectl get ksvc helloworld-elixir --output=custom-columns=NAME:.metadata.name,URL:.status.url

NAME                URL
helloworld-elixir   http://helloworld-elixir.default.1.2.3.4.xip.io

  6. Now you can make a request to your app to see the results. Replace {IP_ADDRESS} with the address you see returned in the previous step.

    ```shell
curl http://helloworld-elixir.default.1.2.3.4.xip.io

...
# HTML from your application is returned.
```

    Here is the HTML returned from our deployed sample application:

    <!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="utf-8">
 <meta http-equiv="X-UA-Compatible" content="IE=edge">
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <meta name="description" content="">
 <meta name="author" content="">

 <title>Hello Knative</title>
 <link rel="stylesheet" type="text/css" href="/css/app-833cc7e8eeed7a7953c5a02e28130dbd.css?vsn=d">
</head>