Tailwind not working in production (no styles just plain html)

Hey folks!
I deployed phoenix 1.6.5 app with tailwindcss to fly.io.
Deploying itself went successfully, but when i visit the app, i got no style. I got just plain html pages.
In the local Machine, tailwindcss works completely fine though.

About deploying, I followed offical guide.
About Tailwindcss, I used Chris Mccord’s library.

I read docs carefully, but I have no clue how to make tailwindcss work properly in production after all.

Dockerfile is like below.

# Find eligible builder and runner images on Docker Hub. We use Ubuntu/Debian instead of
# Alpine to avoid DNS resolution issues in production.
# https://hub.docker.com/r/hexpm/elixir/tags?page=1&name=ubuntu
# https://hub.docker.com/_/ubuntu?tab=tags
# This file is based on these images:
#   - https://hub.docker.com/r/hexpm/elixir/tags - for the build image
#   - https://hub.docker.com/_/debian?tab=tags&page=1&name=bullseye-20210902-slim - for the release image
#   - https://pkgs.org/ - resource for finding needed packages
#   - Ex: hexpm/elixir:1.13.1-erlang-24.2-debian-bullseye-20210902-slim
ARG BUILDER_IMAGE="hexpm/elixir:1.13.1-erlang-24.2-debian-bullseye-20210902-slim"
ARG RUNNER_IMAGE="debian:bullseye-20210902-slim"

FROM ${BUILDER_IMAGE} as builder

# install build dependencies
RUN apt-get update -y && apt-get install -y build-essential git \
    && apt-get clean && rm -f /var/lib/apt/lists/*_*

# prepare build dir

# install hex + rebar
RUN mix local.hex --force && \
    mix local.rebar --force

# set build ENV
ENV MIX_ENV="prod"

# install mix dependencies and tailwind
COPY mix.exs mix.lock ./
RUN mix deps.get --only $MIX_ENV
RUN mkdir config

# copy compile-time config files before we compile dependencies
# to ensure any relevant config change will trigger the dependencies
# to be re-compiled.
COPY config/config.exs config/${MIX_ENV}.exs config/
RUN mix deps.compile

COPY priv priv

# note: if your project uses a tool like https://purgecss.com/,
# which customizes asset compilation based on what it finds in
# your Elixir templates, you will need to move the asset compilation
# step down so that `lib` is available.
COPY assets assets

# compile assets
RUN mix assets.deploy

# Compile the release
COPY lib lib

RUN mix compile

# Changes to config/runtime.exs don't require recompiling the code
COPY config/runtime.exs config/

COPY rel rel
RUN mix release

# start a new build stage so that the final image will only contain
# the compiled release and other runtime necessities

RUN apt-get update -y && apt-get install -y libstdc++6 openssl libncurses5 locales \
  && apt-get clean && rm -f /var/lib/apt/lists/*_*

# Set the locale
RUN sed -i '/en_US.UTF-8/s/^# //g' /etc/locale.gen && locale-gen


WORKDIR "/app"
RUN chown nobody /app

# Only copy the final release from the build stage
COPY --from=builder --chown=nobody:root /app/_build/prod/rel/lv18 ./

USER nobody

CMD ["/app/bin/server"]

# Appended by flyctl
ENV ERL_AFLAGS "-proto_dist inet6_tcp"

fly.toml is like below.

# fly.toml file generated for divine-frog-1067 on 2022-01-12T20:44:28+09:00

app = "divine-frog-1067"

kill_signal = "SIGTERM"
kill_timeout = 5
processes = []

  release_command = "/app/bin/migrate"

  # PHX_HOST = "divine-frog-1067.fly.dev"
  # PORT = "8080"

  allowed_public_ports = []
  auto_rollback = true

  http_checks = []
  internal_port = 4000
  processes = ["app"]
  protocol = "tcp"
  script_checks = []

    hard_limit = 25
    soft_limit = 20
    type = "connections"

    handlers = ["http"]
    port = 80

    handlers = ["tls", "http"]
    port = 443

    grace_period = "30s"
    interval = "15s"
    restart_limit = 0
    timeout = "2s"

runtime.exs is like below.

import Config

# config/runtime.exs is executed for all environments, including
# during releases. It is executed after compilation and before the
# system starts, so it is typically used to load production configuration
# and secrets from environment variables or elsewhere. Do not define
# any compile-time configuration in here, as it won't be applied.
# The block below contains prod specific runtime configuration.
if config_env() == :prod do
  database_url =
    System.get_env("DATABASE_URL") ||
      raise """
      environment variable DATABASE_URL is missing.
      For example: ecto://USER:PASS@HOST/DATABASE
  app_name =
    System.get_env("FLY_APP_NAME") ||
      raise "FLY_APP_NAME not available"

  config :lv18, Lv18.Repo,
    # ssl: true,
    socket_options: [:inet6],
    url: database_url,
    pool_size: String.to_integer(System.get_env("POOL_SIZE") || "10")

  # The secret key base is used to sign/encrypt cookies and other secrets.
  # A default value is used in config/dev.exs and config/test.exs but you
  # want to use a different value for prod and you most likely don't want
  # to check this value into version control, so we use an environment
  # variable instead.
  secret_key_base =
    System.get_env("SECRET_KEY_BASE") ||
      raise """
      environment variable SECRET_KEY_BASE is missing.
      You can generate one by calling: mix phx.gen.secret

  config :lv18, Lv18Web.Endpoint,
    server: true,
    url: [host: "#{app_name}.fly.dev", port: 80],
    http: [
      # Enable IPv6 and bind on all interfaces.
      # Set it to  {0, 0, 0, 0, 0, 0, 0, 1} for local network only access.
      # See the documentation on https://hexdocs.pm/plug_cowboy/Plug.Cowboy.html
      # for details about using IPv6 vs IPv4 and loopback vs public addresses.
      ip: {0, 0, 0, 0, 0, 0, 0, 0},
      port: String.to_integer(System.get_env("PORT") || "4000")
    secret_key_base: secret_key_base

  # ## Using releases
  # If you are doing OTP releases, you need to instruct Phoenix
  # to start each relevant endpoint:
  #     config :lv18, Lv18Web.Endpoint, server: true
  # Then you can assemble a release by calling `mix release`.
  # See `mix help release` for more information.

  # ## Configuring the mailer
  # In production you need to configure the mailer to use a different adapter.
  # Also, you may need to configure the Swoosh API client of your choice if you
  # are not using SMTP. Here is an example of the configuration:
  #     config :lv18, Lv18.Mailer,
  #       adapter: Swoosh.Adapters.Mailgun,
  #       api_key: System.get_env("MAILGUN_API_KEY"),
  #       domain: System.get_env("MAILGUN_DOMAIN")
  # For this example you need include a HTTP client required by Swoosh API client.
  # Swoosh supports Hackney and Finch out of the box:
  #     config :swoosh, :api_client, Swoosh.ApiClient.Hackney
  # See https://hexdocs.pm/swoosh/Swoosh.html#module-installation for details.

config.exs is like below.

import Config

# For production, don't forget to configure the url host
# to something meaningful, Phoenix uses this information
# when generating URLs.
# Note we also include the path to a cache manifest
# containing the digested version of static files. This
# manifest is generated by the `mix phx.digest` task,
# which you should run after static files are built and
# before starting your production server.
config :lv18, Lv18Web.Endpoint,
  url: [host: "example.com", port: 80],
  cache_static_manifest: "priv/static/cache_manifest.json"

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

# ## SSL Support
# To get SSL working, you will need to add the `https` key
# to the previous section and set your `:url` port to 443:
#     config :lv18, Lv18Web.Endpoint,
#       ...,
#       url: [host: "example.com", port: 443],
#       https: [
#         ...,
#         port: 443,
#         cipher_suite: :strong,
#         keyfile: System.get_env("SOME_APP_SSL_KEY_PATH"),
#         certfile: System.get_env("SOME_APP_SSL_CERT_PATH")
#       ]
# The `cipher_suite` is set to `:strong` to support only the
# latest and more secure SSL ciphers. This means old browsers
# and clients may not be supported. You can set it to
# `:compatible` for wider support.
# `:keyfile` and `:certfile` expect an absolute path to the key
# and cert in disk or a relative path inside priv, for example
# "priv/ssl/server.key". For all supported SSL configuration
# options, see https://hexdocs.pm/plug/Plug.SSL.html#configure/1
# We also recommend setting `force_ssl` in your endpoint, ensuring
# no data is ever sent via http, always redirecting to https:
#     config :lv18, Lv18Web.Endpoint,
#       force_ssl: [hsts: true]
# Check `Plug.SSL` for all available options in `force_ssl`.

Thanks! :smiley:

You need to move this line above the assets.deploy one:

COPY lib lib

We do this on master now when generating the Dockerfile for phx.gen.release --docker, but the tldr; is tailwind needs to have access to the lib/app_web directory to build the styles from your file patterns in the tailwind config. Since lib is copied after running assets.deploy in your docker file, it won’t see any of your files and thus won’t produce any included classes. Move that to after the deploy command and you are golden!


Thank you for replying!

I changed Dockerfile as you described and deployed it to fly.io couple of times, but still tailwindcss doesn’t work properly.


# Compile the release
COPY lib lib

# compile assets
RUN mix assets.deploy

# Compile the release
# COPY lib lib

I am really grateful that you are working on this by the way!

Hi @amadeus,

Your issue sounds like something I have encountered in the past… Can you please share your tailwind.config.js file?

1 Like


I recently updated my Phoenix app to use Tailwind without NPM, here is what I did Removing NPM from Phoenix and using Tailwind.

Hope it helps, if not let me know and I will see if I can help.



Hi, @trisolaran !

My tailwind.config.js is here! i didn’t change anything!

// See the Tailwind configuration guide for advanced usage
// https://tailwindcss.com/docs/configuration
module.exports = {
  content: [
  theme: {
    extend: {},
  plugins: [

Hi, @andrewb !

Your post looks super helpful, i am going to give it a try from now on! Thank you for sharing!!

Did you also remove the app.css import from app.js? Does the tailwind build work locally?

1 Like

Please also make sure you are on the latest tailwind

1 Like

Hi, @chrismccord !

After I removed import app.css from app.js, EVERYTHING works properly finally!!!

Thank you so so so much!!

@trisolaran , @andrewb
Thank you so much for replying me! This is my first topic on elixirforum!
This experience is priceless!