Browsersync within a Docker container

I've got a Wordpress/MySQL docker container, which I use for developing themes & plugins. I access this on localhost:8000.

It uses a Gulp build process & I am trying to add browsersync to the mix. I'm having a hard time getting the browsersync to actually proxy out of the container. From the Gulp output I can see that its generating the changes, just not actually making any changes in the browser.

Heres my docker-compose.yml, gulpfile, dockerfile & shell script.

version: '2'

services:
    wordpress_db:
        image: mariadb
        restart: 'always'
        ports:
            - 3360:3306
        volumes:
            - ./db_data:/docker-entrypoint-initdb.d
        environment:
            MYSQL_ROOT_PASSWORD: wordpress
            MYSQL_DATABASE: wordpress

    wordpress:
        depends_on:
            - wordpress_db
        image: wordpress
        restart: 'always'
        environment:
            WORDPRESS_DB_NAME: wordpress
            WORDPRESS_DB_USER: root
            WORDPRESS_DB_PASSWORD: wordpress
        ports:
            - 8000:3000
        volumes:
            - ./uploads:/var/www/html/wp-content/uploads
            - ./plugins:/var/www/html/wp-content/plugins
            - ./theme:/var/www/html/wp-content/themes/theme
        links:
            - wordpress_db:mysql

    composer:
        image: composer/composer:php7
        depends_on:
            - wordpress
        restart: 'no'
        environment:
            ACF_PRO_KEY: this_would_be_my_ACF_pro_key_:)
        volumes_from:
            - wordpress
        working_dir: /var/www/html/wp-content/themes/theme
        command: install

    node:
        restart: 'no'
        image: node:slim
        depends_on:
            - wordpress
        volumes_from:
            - wordpress
        working_dir: /var/www/html/wp-content/themes/theme
        build:
            context: .
            dockerfile: WordpressBuild
            args:
                - SITE_VERSION=0.0.1

var browserSync  = require('browser-sync');
var reload      = browserSync.reload;
var watchify     = require('watchify');
var browserify   = require('browserify');
var source       = require('vinyl-source-stream');
var buffer       = require('vinyl-buffer');
var gulp         = require('gulp');
var gutil        = require('gulp-util');
var gulpSequence = require('gulp-sequence');
var processhtml  = require('gulp-minify-html');
var sass         = require('gulp-sass');
var autoprefixer = require('gulp-autoprefixer');
var watch        = require('gulp-watch');
var cleanCSS    = require('gulp-clean-css');
var uglify       = require('gulp-uglify');
var streamify    = require('gulp-streamify');
var sourcemaps   = require('gulp-sourcemaps');
var concat       = require('gulp-concat');
var babel        = require('gulp-babel');
var fontawesome  = require('node-font-awesome');
var prod         = gutil.env.prod;

var onError = function(err) {
  console.log(err.message);
  this.emit('end');
};

// bundling js with browserify and watchify
var b = watchify(browserify('./src/js/app', {
  cache: {},
  packageCache: {},
  fullPaths: true
}));

gulp.task('js', bundle);
b.on('update', bundle);
b.on('log', gutil.log);

function bundle() {
  return b.bundle()
    .on('error', onError)
    .pipe(source('app.js'))
    .pipe(buffer())
    .pipe(sourcemaps.init())
    .pipe(prod ? babel({
      presets: ['es2015']
    }) : gutil.noop())
    .pipe(concat('app.js'))
    .pipe(!prod ? sourcemaps.write('.') : gutil.noop())
    .pipe(prod ? streamify(uglify()) : gutil.noop())
    .pipe(gulp.dest('./assets/js'))
    .pipe(browserSync.stream());
}

// fonts
gulp.task('fonts', function() {
  gulp.src(fontawesome.fonts)
    .pipe(gulp.dest('./assets/fonts'));
});

// sass
gulp.task('sass', function() {
  return gulp.src('./src/scss/**/*.scss')
    .pipe(sourcemaps.init())
      .pipe(sass({
        includePaths: [].concat(require('node-bourbon').includePaths, ['node_modules/foundation-sites/scss', 'node_modules/motion-ui/src', fontawesome.scssPath])
      }))
      .on('error', onError)
      .pipe(prod ? cleanCSS() : gutil.noop())
      .pipe(prod ? autoprefixer({
        browsers: ['last 2 versions'],
        cascade: false
      }) : gutil.noop())
    .pipe(!prod ? sourcemaps.write('.') : gutil.noop())
    .pipe(gulp.dest('./assets/css'))
    .pipe(browserSync.stream());
});

gulp.task('watch', function(){
  gulp.watch('./src/scss/**/*.scss', ['sass']);
  gulp.watch('./src/js/**/*.js', ['js']);
});

// browser-sync task for starting the server.
gulp.task('serve', function() {
    //watch files
    var files = [
    './assets/css/*.scss',
    './*.php'
    ];

    //initialize browsersync
    browserSync.init(files, {
    //browsersync with a php server
    proxy: "localhost",
    notify: false
  });
  gulp.watch('./src/scss/**/*.scss', ['sass']);

    // gulp.task('default', gulpSequence(['fonts', 'sass', 'js', 'watch']));
});

// use gulp-sequence to finish building html, sass and js before first page load
gulp.task('default', gulpSequence(['fonts', 'sass', 'js'], 'serve'));

The docker-compose.yml refers to the following dockerfile:

FROM node

# Grab our version variable from the yml file
ARG SITE_VERSION

# Install gulp globally
RUN npm install -g gulp node-gyp node-sass

# Install dependencies
COPY ./gulp-build.sh /
RUN chmod 777 /gulp-build.sh
ENTRYPOINT ["/gulp-build.sh"]
CMD ["run"]

which installs gulp and node-sass, and also copies the following gulp-guild.sh script into the container:

#!/bin/bash

cd /var/www/html/wp-content/themes/theme
# npm rebuild node-sass && npm install && gulp --dev
npm rebuild node-sass && npm install && gulp

The primary problem with your configuration is that you're pointing to localhost in the gulpfile. This points to the local container, not your host machine, so browsersync won't be able to connect to Wordpress.

You first need to update the gulpfile to point to the wordpress service, on its internal port:

browserSync.init(files, {
    // The hostname is the name of your service in docker-compose.yml.
    // The port is what's defined in your Dockerfile.
    proxy: "wordpress:3000",
    notify: false,
    // Do not open browser on start
    open: false
})

Then you need to add a port mapping to expose the browsersync server from your node service. In your docker-compose.yml file:

node:
    ports:
        - "3000:3000"
        - "3001:3001"

You should now be able to access the browsersync proxy on localhost:3001.

P.S. In case you have more than one site serving in one ngninx docker container, you can edit nginx config file for specific site in /etc/nginx/conf.d/somesite.conf and add new line: listen: 3000;