Hello everyone,

I am learning Phoenix/Elixir and I am trying to dockerize my app so that I can deploy to AWS, but I keep getting all kinds of errors.

I am getting this error:

Recreating myapp_web_1_f59b1c3a118c ... done
Attaching to myapp_web_1_f59b1c3a118c
web_1_f59b1c3a118c | "ecto://postgres:alejandro1@localhost/appexo_prod"
web_1_f59b1c3a118c | 18:45:11.435 [error] Postgrex.Protocol (#PID<0.2424.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
...
web_1_f59b1c3a118c | 18:45:11.438 [error] Postgrex.Protocol (#PID<0.2417.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (localhost:5432): connection refused - :econnrefused
web_1_f59b1c3a118c | 18:45:11.443 [info] Running MyappWeb.Endpoint with cowboy 2.6.3 at :::4000 (http)
web_1_f59b1c3a118c | 18:45:11.443 [info] Access MyappWeb.Endpoint at http://localhost:4000
^CGracefully stopping... (press Ctrl+C again to force)
Stopping myapp_web_1_f59b1c3a118c   ... 
Killing myapp_web_1_f59b1c3a118c    ... done

The Endpoint is wrong and connection is refused.
Here is my prod.exs

use Mix.Config

config :myapp, MyappWeb.Endpoint,
  http: [:inet6, port: System.get_env("PORT") || 4000],
  url: [host: "localhost", port: System.get_env("PORT")],
  cache_static_manifest: "priv/static/cache_manifest.json",
  secret_key_base: System.get_env("SECRET_KEY_BASE"),
  server: true,
  root: "."

# Do not print debug messages in production
config :logger, level: :info

# Configure your database
config :myapp, Myapp.Repo,
  adapter: Ecto.Adapters.Postgres,
  # hostname: System.get_env("DATABASE_HOST"),
  # username: System.get_env("DATABASE_USER"),
  # password: System.get_env("DATABASE_PASS"),
  # database: System.get_env("DATABASE_NAME"),
  url: System.get_env("DATABASE_URL"),
  pool_size: 10

# import_config "prod.secret.exs"

My docker-compose.yml

version: '3.5'

services:
  web:
    image: "myapp:latest"
    ports:
      - "80:4000" # In our .env file above, we chose port 4000
    env_file:
      - config/docker.env

My config/config.exs

use Mix.Config

config :myapp,
  ecto_repos: [Myapp.Repo]

# Configures the endpoint
config :myapp, MyappWeb.Endpoint,
  url: [host: "localhost"],
  secret_key_base: "RXyklAFqTajbz7dePdeEHa/sLLbMORcUeY/GshZsKnXJIZ7eSTnKQq22DRoCkTO/",
  render_errors: [view: AppexoWeb.ErrorView, accepts: ~w(json)],
  pubsub: [name: Appexo.PubSub, adapter: Phoenix.PubSub.PG2]
.........
import_config "#{Mix.env()}.exs"

My Dockerfile:

# The version of Alpine to use for the final image
# This should match the version of Alpine that the `elixir:1.7.2-alpine` image uses
ARG ALPINE_VERSION=3.9

FROM elixir:1.8.2-alpine AS builder

# The following are build arguments used to change variable parts of the image.
# The name of your application/release (required)
ARG APP_NAME=myapp
# Database Url
ARG DATABASE_URL=ecto://postgres:xxxxxxxxxx@localhost/my_db
# The version of the application we are building (required)
ARG APP_VSN=0.1.0
# The environment to build with
ARG MIX_ENV=prod
# Set this to true if this release is not a Phoenix app
ARG SKIP_PHOENIX=false
# If you are using an umbrella project, you can change this
# argument to the directory the Phoenix app is in so that the assets
# can be built
ARG PHOENIX_SUBDIR=.

ENV SKIP_PHOENIX=${SKIP_PHOENIX} \
    APP_NAME=${APP_NAME} \
    APP_VSN=${APP_VSN} \
    MIX_ENV=${MIX_ENV} \
    DATABASE_URL=${DATABASE_URL}

# By convention, /opt is typically used for applications
WORKDIR /opt/app

# This step installs all the build tools we'll need
RUN apk update && \
  apk upgrade --no-cache && \
  apk add --no-cache \
    nodejs \
    yarn \
    git \
    build-base && \
  mix local.rebar --force && \
  mix local.hex --force

# This copies our app source code into the build container
COPY . .

RUN mix do deps.get, deps.compile, compile

# This step builds assets for the Phoenix app (if there is one)
# If you aren't building a Phoenix app, pass `--build-arg SKIP_PHOENIX=true`
# This is mostly here for demonstration purposes
RUN if [ ! "$SKIP_PHOENIX" = "true" ]; then \
  cd ${PHOENIX_SUBDIR}/assets && \
  yarn install && \
  yarn deploy && \
  cd - && \
  mix phx.digest; \
fi

RUN \
  mkdir -p /opt/built && \
  mix distillery.release --verbose && \
  cp _build/${MIX_ENV}/rel/${APP_NAME}/releases/${APP_VSN}/${APP_NAME}.tar.gz /opt/built && \
  cd /opt/built && \
  tar -xzf ${APP_NAME}.tar.gz && \
  rm ${APP_NAME}.tar.gz

# From this line onwards, we're in a new image, which will be the image used in production
FROM alpine:${ALPINE_VERSION}

# The name of your application/release (required)
ARG APP_NAME=myapp
# Database Url
ARG DATABASE_URL=ecto://postgres:xxxxxxx@localhost/mydb

RUN apk update && \
    apk add --no-cache \
      bash \
      openssl-dev

ENV REPLACE_OS_VARS=true \
    APP_NAME=${APP_NAME} \
    DATABASE_URL=${DATABASE_URL}

WORKDIR /opt/app

COPY --from=builder /opt/built .

CMD trap 'exit' INT; DATABASE_URL=${DATABASE_URL} /opt/app/bin/${APP_NAME} foreground

My repo.ex

defmodule Myapp.Repo do
  use Ecto.Repo,
    otp_app: :myapp,
    adapter: Ecto.Adapters.Postgres

  def init(_type, config) do
    database_url = System.get_env("DATABASE_URL")
    IO.inspect(database_url)

    if database_url == nil do
      {:ok, config}
    else
      {:ok, Keyword.put(config, :url, database_url)}
    end
  end
end

rel/config.exs

...

environment :prod do
  set include_erts: true
  set include_src: false
  set cookie: :"..................."
  # set vm_args: "rel/vm.args"
end

release :myapp do
  set version: current_version(:appexo)
  set applications: [
    :runtime_tools
  ]

  set config_providers: [
    {Distillery.Releases.Config.Providers.Elixir, ["${RELEASE_ROOT_DIR}/etc/config.exs"]}
  ]
  set overlays: [
    {:copy, "rel/config/config.exs", "etc/config.exs"}
  ]
end

And my rel/config/config.exs

use Mix.Config

config :myapp, Myapp.Repo,
  # username: System.get_env("DATABASE_USER"),
  # password: System.get_env("DATABASE_PASS"),
  # database: System.get_env("DATABASE_NAME"),
  # hostname: System.get_env("DATABASE_HOST"),
  url: System.get_env("DATABASE_URL"),
  pool_size: 10

port = String.to_integer(System.get_env("PORT") || "8080")
config :appexo, Appexo.Endpoint,
  http: [port: port],
  url: [host: "localhost", port: port],
  root: ".",
  secret_key_base: System.get_env("SECRET_KEY_BASE")

Also docker.env

HOSTNAME=localhost
SECRET_KEY_BASE="u1QXlca4XEZKb1o3HL/aUlznI1qstCNAQ6yme/lFbFIs0Iqiq/annZ+Ty8JyUCDc"
DATABASE_HOST=db
DATABASE_USER=postgres
DATABASE_PASS=xxxxxxx
DATABASE_NAME=my_db
DATABASE_URL=ecto://postgres:xxxxxxx@localhost/my_db
PORT=4000
LANG=en_US.UTF-8
REPLACE_OS_VARS=true

I have tried a lot of things… What am I doing wrong??