# Hello World - Elixir

A simple web application written in [Elixir](https://elixir-lang.org/) using the
[Phoenix Framework](https://phoenixframework.org/). The application prints all
environment variables to the main page.

## Set up Elixir and Phoenix Locally

Following the
[Phoenix Installation Guide](https://hexdocs.pm/phoenix/installation.html) 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`](http://localhost:4000) from your browser.

## Recreating the sample code

1. Generate a new project.

    ```bash
    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`

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

   ```docker
   # 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"]
   ```

1. 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.

   ```yaml
   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.

    ```bash
    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
    ```

1.  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:

    ```bash
    # Build and push the container on your local machine.
    docker buildx build --platform linux/arm64,linux/amd64 -t "{username}/helloworld-elixir" --push .
    ```

1.  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`:

    ```bash
    kubectl apply --filename service.yaml
    ```

1.  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).

1.  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.sslip.io
    ```

1.  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.

        ```bash
        curl http://helloworld-elixir.default.1.2.3.4.sslip.io

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

    Here is the HTML returned from our deployed sample application:

    ```HTML
    <!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>

      <body>
        <div class="container">
          <header class="header">
            <nav role="navigation">

            </nav>
          </header>

          <p class="alert alert-info" role="alert"></p>
          <p class="alert alert-danger" role="alert"></p>

          <main role="main">

            <div class="jumbotron">
              <h2>Welcome to Knative and Elixir</h2>

              <p>$TARGET = elixir Sample v1</p>
            </div>

            <h3>Environment</h3>
            <ul>
              <li>BINDIR = /opt/app/erts-9.3.2/bin</li>
              <li>DEST_SYS_CONFIG_PATH = /opt/app/var/sys.config</li>
              <li>DEST_VMARGS_PATH = /opt/app/var/vm.args</li>
              <li>DISTILLERY_TASK = foreground</li>
              <li>EMU = beam</li>
              <li>ERL_LIBS = /opt/app/lib</li>
              <li>ERL_OPTS = </li>
              <li>ERTS_DIR = /opt/app/erts-9.3.2</li>
              <li>ERTS_LIB_DIR = /opt/app/erts-9.3.2/../lib</li>
              <li>ERTS_VSN = 9.3.2</li>
              <li>HELLOWORLD_ELIXIR_00001_SERVICE_PORT = tcp://10.35.241.50:80</li>
              <li>HELLOWORLD_ELIXIR_00001_SERVICE_PORT_80_TCP = tcp://10.35.241.50:80</li>
              <li>HELLOWORLD_ELIXIR_00001_SERVICE_PORT_80_TCP_ADDR = 10.35.241.50</li>
              <li>HELLOWORLD_ELIXIR_00001_SERVICE_PORT_80_TCP_PORT = 80</li>
              <li>HELLOWORLD_ELIXIR_00001_SERVICE_PORT_80_TCP_PROTO = tcp</li>
              <li>HELLOWORLD_ELIXIR_00001_SERVICE_SERVICE_HOST = 10.35.241.50</li>
              <li>HELLOWORLD_ELIXIR_00001_SERVICE_SERVICE_PORT = 80</li>
              <li>HELLOWORLD_ELIXIR_00001_SERVICE_SERVICE_PORT_HTTP = 80</li>
              <li>HELLOWORLD_ELIXIR_PORT = tcp://10.35.253.90:80</li>
              <li>HELLOWORLD_ELIXIR_PORT_80_TCP = tcp://10.35.253.90:80</li>
              <li>HELLOWORLD_ELIXIR_PORT_80_TCP_ADDR = 10.35.253.90</li>
              <li>HELLOWORLD_ELIXIR_PORT_80_TCP_PORT = 80</li>
              <li>HELLOWORLD_ELIXIR_PORT_80_TCP_PROTO = tcp</li>
              <li>HELLOWORLD_ELIXIR_SERVICE_HOST = 10.35.253.90</li>
              <li>HELLOWORLD_ELIXIR_SERVICE_PORT = 80</li>
              <li>HELLOWORLD_ELIXIR_SERVICE_PORT_HTTP = 80</li>
              <li>HOME = /root</li>
              <li>HOSTNAME = helloworld-elixir-00001-deployment-84f68946b4-76hcv</li>
              <li>KUBERNETES_PORT = tcp://10.35.240.1:443</li>
              <li>KUBERNETES_PORT_443_TCP = tcp://10.35.240.1:443</li>
              <li>KUBERNETES_PORT_443_TCP_ADDR = 10.35.240.1</li>
              <li>KUBERNETES_PORT_443_TCP_PORT = 443</li>
              <li>KUBERNETES_PORT_443_TCP_PROTO = tcp</li>
              <li>KUBERNETES_SERVICE_HOST = 10.35.240.1</li>
              <li>KUBERNETES_SERVICE_PORT = 443</li>
              <li>KUBERNETES_SERVICE_PORT_HTTPS = 443</li>
              <li>LD_LIBRARY_PATH = /opt/app/erts-9.3.2/lib:</li>
              <li>MIX_ENV = prod</li>
              <li>NAME = hello@127.0.0.1</li>
              <li>NAME_ARG = -name hello@127.0.0.1</li>
              <li>NAME_TYPE = -name</li>
              <li>OLDPWD = /opt/app</li>
              <li>OTP_VER = 20</li>
              <li>PATH = /opt/app/erts-9.3.2/bin:/opt/app/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin</li>
              <li>PORT = 8080</li>
              <li>PROGNAME = opt/app/releases/0.0.1/hello.sh</li>
              <li>PWD = /opt/app</li>
              <li>RELEASES_DIR = /opt/app/releases</li>
              <li>RELEASE_CONFIG_DIR = /opt/app</li>
              <li>RELEASE_ROOT_DIR = /opt/app</li>
              <li>REL_NAME = hello</li>
              <li>REL_VSN = 0.0.1</li>
              <li>REPLACE_OS_VARS = true</li>
              <li>ROOTDIR = /opt/app</li>
              <li>RUNNER_LOG_DIR = /var/log</li>
              <li>RUN_ERL_ENV = </li>
              <li>SHLVL = 1</li>
              <li>SRC_SYS_CONFIG_PATH = /opt/app/releases/0.0.1/sys.config</li>
              <li>SRC_VMARGS_PATH = /opt/app/releases/0.0.1/vm.args</li>
              <li>SYS_CONFIG_PATH = /opt/app/var/sys.config</li>
              <li>TARGET = elixir Sample v1</li>
              <li>TERM = xterm</li>
              <li>VMARGS_PATH = /opt/app/var/vm.args</li>
            </ul>
          </main>

        </div> <!-- /container -->
        <script src="/js/app-930ab1950e10d7b5ab5083423c28f06e.js?vsn=d"></script>

      </body>
    </html>
    ```

## Removing the sample app deployment

To remove the sample app from your cluster, delete the service record:

```bash
kubectl delete --filename service.yaml
```
