Structuring the Docker setup for PHP Projects

... folder structure, Dockerfile templates and general fundamentals

Posted by Pascal Landau on 2019-05-20 10:00:00

In the third part of this tutorial series on developing PHP on Docker we'll lay the fundamentals to build a complete development infrastructure and explain how to "structure" the Docker setup as part of a PHP project. Structure as in

  • folder structure ("what to put where")
  • Dockerfile templates
  • solving common problems (file permissions, runtime configuration, ...)

We will also create a minimal container setup consisting of php-fpm, nginx and a workspace container that we refactor from the previous parts of this tutorial.

Published parts of the Docker PHP Tutorial

All code samples are publicly available in my Docker PHP Tutorial repository on github. The branch for this tutorial is part_3_structuring-the-docker-setup-for-php-projects.

If you want to follow along, please subscribe to the RSS feed or via email to get automatic notifications when the next part comes out :)


Shout out to Nils Meyer for giving the final "[...] nichts offensichtlich falsch" ("nothing obviously wrong") :)

Table of contents


When I started my current role as Head of Marketing Technology at ABOUT YOU back in 2016, we heavily relied on Vagrant (namely: Homestead) as our development infrastructure. Though that was much better than working on our local machines, we've run into a couple of problems along the way (e.g. diverging software, bloated images, slow starting times, complicated readme for onboarding, upgrading php, ...).

Today, everything that we need for the infrastructure is under source control and committed in the same repository that we use for our main application. In effect we get the same infrastructure for every developer including automatic updates "for free". It is extremely easy to tinker around with updates / new tools due to the ephemeral nature of docker as tear down and rebuild only take one command and a couple of minutes.

To get a feeling for how the process feels like, simply execute the following commands.

git clone
cd docker-php-tutorial
git checkout part_3_structuring-the-docker-setup-for-php-projects
make docker-clean
make docker-init
make docker-build-from-scratch
make docker-test

You should now have a running docker environment to develop PHP on docker (unless something is blocking your port 80/443 or you don't have make installed ;))

Structuring the repository

While playing around with docker I've tried different ways to "structure" files and folders and ended up with the following concepts:

  • everything related to docker is placed in a .docker directory on on the same level as the main application
  • in this directory
    • each service gets its own subdirectory for configuration
    • is a .shared folder containing scripts and configuration required by multiple services
    • is an .env.example file containing variables for the docker-compose.yml
    • is a file containing high level tests to validate the docker containers
  • a Makefile with common instructions to control Docker is placed in the repository root

The result looks roughly like this:

├── .docker/
|   ├── .shared/
|   |   ├── config/
|   |   └── scripts/
|   ├── php-fpm/
|   |   └── Dockerfile
|   ├── ... <additional services>/
|   ├── .env.example
|   ├── docker-compose.yml
|   └──
├── Makefile
├── index.php
└──  ... <additional app files>/

The .docker folder

As I mentioned, for me it makes a lot of sense to keep the infrastructure definition close to the codebase, because it is immediately available to every developer. For bigger projects with multiple components there will be a code-infrastructure-coupling anyways (e.g. in my experience it is usually not possible to simply switch MySQL for PostgreSQL without any other changes) and for a library it is a very convenient (although opinionated) way to get started.

I personally find it rather frustrating when I want to contribute to an open source project but find myself spending a significant amount of time setting the environment up correctly instead of being able to just work on the code.

Ymmv, though (e.g. because you don't want everybody with write access to your app repo also to be able to change your infrastructure code). We actually went a different route previously and had a second repository ("-inf") that would contain the contents of the .docker folder:

├── .shared/
|   ├── config/
|   └── scripts/
├── php-fpm/
|   └── Dockerfile
├── ... <additional services>/
├── .env.example
└──  docker-compose.yml

├── index.php
└──  ... <additional app files>/

Worked as well, but we often ran into situations where the contents of the repo would be stale for some devs, plus it was simply additional overhead with not other benefits to us at that point. Maybe git submodules will enable us to get the best of both worlds - I'll blog about it once we try ;)

The .shared folder

When dealing with multiple services, chances are high that some of those services will be configured similarly, e.g. for

  • installing common software
  • setting up unix users (with the same ids)
  • configuration (think php-cli for workers and php-fpm for web requests)

To avoid duplication, I place scripts (simple bash files) and config files in the .shared folder and make it available in the build context for each service. I'll explain the process in more detail under providing the correct build context.

Is really just a simple bash script that includes some high level tests to make sure that the containers are built correctly. See section Testing if everything works.

.env.example and docker-compose.yml

docker-compose uses a .env file for a convenient way to define and substitute environment variables. Since this .env file is environment specific, it is NOT part of the repository (i.e. ignored via .gitignore). Instead, we provide a .env.example file that contains the required environment variables including reasonable default values. A new dev would usually run cp .env.example .env after checking out the repository for the first time. See section .env.example.

The Makefile

make and Makefiles are among those things that I've heard about occasionally but never really cared to understand (mostly because I associated them with C). Boy, did I miss out. I was comparing different strategies to provide code quality tooling (style checkers, static analyzers, tests, ...) and went from custom bash scripts over composer scripts to finally end up at Makefiles.

The Makefile serves as a central entry point and simplifies the management of the docker containers, e.g. for (re-)building, starting, stopping, logging in, etc. See section Makefile and .bashrc.

Defining services: php-fpm, nginx and workspace

Let's have a look at a real example and "refactor" the php-cli, php-fpm and nginx containers from the first part of this tutorial series.

This is the folder structure:

├── .docker/
|   ├── .shared/
|   |   ├── config/
|   |   |   └── php/ 
|   |   |       └── conf.d/
|   |   |           └── zz-app.ini
|   |   └── scripts/
|   |       └── docker-entrypoint/
|   |           └──
|   ├── nginx/
|   |   ├── sites-available/
|   |   |   └── default.conf
|   |   ├── Dockerfile
|   |   └── nginx.conf
|   ├── php-fpm/
|   |   ├── php-fpm.d/
|   |   |   └── pool.conf
|   |   └── Dockerfile
|   ├── workspace/ (formerly php-cli)
|   |   ├── .ssh/
|   |   |   └── insecure_id_rsa
|   |   |   └──
|   |   └── Dockerfile
|   ├── .env.example
|   ├── docker-compose.yml
|   └──
├── Makefile
└── index.php


Click here to see the full php-fpm Dockerfile.

Since we will be having two PHP containers, we need to place the common .ini settings in the .shared directory.

|   ├── .shared/
|   |   ├── config/
|   |   |   └── php/ 
|   |   |       └── conf.d/
|   |   |           └── zz-app.ini

For now, zz-app.ini will only contain our opcache setup:

; enable opcache
opcache.enable_cli = 1
opcache.enable = 1
opcache.fast_shutdown = 1
; revalidate everytime (effectively disabled for development)
opcache.validate_timestamps = 0

The pool configuration is only relevant for php-fpm, so it goes in the directory of the service. Btw. I highly recommend this video on PHP-FPM Configuration if your php-fpm foo isn't already over 9000.

|   ├── php-fpm/
|   |   ├── php-fpm.d/
|   |   |   └── pool.conf

Modifying the pool configuration

We're using the script to set the user and group that owns the php-fpm processes.

# php-fpm pool config
COPY ${SERVICE_DIR}/php-fpm.d/* /usr/local/etc/php-fpm.d
RUN /tmp/scripts/ /usr/local/etc/php-fpm.d/zz-default.conf \
    "__APP_USER" \
    "${APP_USER}" \
 && /tmp/scripts/ /usr/local/etc/php-fpm.d/zz-default.conf \
    "__APP_GROUP" \
    "${APP_GROUP}" \


Since php-fpm needs to be debuggable, we need to ensure that the host.docker.internal DNS entry exists, so we'll use the corresponding ENTRYPOINT to do that.

# entrypoint
RUN mkdir -p /bin/docker-entrypoint/ \
 && cp /tmp/scripts/docker-entrypoint/* /bin/docker-entrypoint/ \
 && chmod +x -R /bin/docker-entrypoint/ \

ENTRYPOINT ["/bin/docker-entrypoint/","php-fpm"]


Click here to see the full nginx Dockerfile.

The nginx setup is even simpler. There is no shared config, so that everything we need resides in

|   ├── nginx/
|   |   ├── sites-available/
|   |   |   └── default.conf
|   |   ├── Dockerfile
|   |   └── nginx.conf

Please note, that nginx only has the nginx.conf file for configuration (i.e. there is no conf.d directory or so), so we need to define the full config in there.

worker_processes 4;
pid /run/;
daemon off;

http {
  # ...

  include /etc/nginx/sites-available/*.conf;

  # ...

There are two things to note:

  • user and group are modified dynamically
  • we specify /etc/nginx/sites-available/ as the directory that holds the config files for the individual files via include /etc/nginx/sites-available/*.conf;

We need to keep the last point in mind, because we must use the same directory in the Dockerfile:

# nginx app config
COPY ${SERVICE_DIR}/sites-available/* /etc/nginx/sites-available/

The site's config file default.conf has a variable (__NGINX_ROOT) for the root directive and we "connect" it with the fpm-container via fastcgi_pass php-fpm:9000;

server {
    # ...
    root __NGINX_ROOT;
    # ...

    location ~ \.php$ {
        # ...
        fastcgi_pass php-fpm:9000;

php-fpm will resolve to the php-fpm container, because we use php-fpm as the service name in the docker-compose file, so it will be automatically used as the hostname:

Other containers on the same network can use either the service name or [an] alias to connect to one of the service’s containers.

In the Dockerfile, we use

RUN /tmp/scripts/ /etc/nginx/sites-available/default.conf \
    "__NGINX_ROOT" \
    "${APP_CODE_PATH}" \

APP_CODE_PATH will be passed via docker-compose when we build the container and mounted as a shared directory from the host system.

workspace (formerly php-cli)

Click here to see the full workspace Dockerfile.

We will use the former php-cli container and make it our workspace as introduced in part 2 of this tutorial under Preparing the "workspace" container.

This will be the container we use to point our IDE to, e.g. to execute tests. Its Dockerfile looks almost identical to the one of the php-fpm service, apart from the SSH setup:

# set up ssh
RUN apt-get update -yqq && apt-get install -yqq openssh-server \
 && mkdir /var/run/sshd \

# add default public key to authorized_keys
COPY ${SERVICE_DIR}/.ssh/ /tmp/
RUN mkdir -p ~/.ssh \
 && cat /tmp/ >> ~/.ssh/authorized_keys \
 && chown -R ${APP_USER}: ~/.ssh \
 && chmod 700 ~/.ssh \
 && chmod 600 ~/.ssh/authorized_keys \
USER root

Setting up docker-compose

In order to orchestrate the build process, we'll use docker-compose.


See the full docker-compose.yml file in the repository

Things to note:

  • each service uses context: . so it has access to the .shared folder. The context is always relative to the location of the first docker-compose.yml file
  • all arguments that we used in the Dockerfiles are defined in the args: section via
    - TZ=${TIMEZONE}
  • the codebase is synced from the host in all containers via
  • the nginx service exposes ports on the host machine so that we can access the containers from "outside" via
    - "${NGINX_HOST_HTTP_PORT}:80"
    - "${NGINX_HOST_HTTPS_PORT}:443"
  • all services are part of the backend network so they can talk to each other. The nginx service has an additional alias that allows us to define an arbitrary host name via
        - ${APP_HOST}

    I prefer to have a dedicated hostname per project (e.g. docker-php-tutorial.local) instead of using or localhost directly


To fill in all the required variables / arguments, we're using a .env.example file with the following content:

# Default settings for docker-compose

# build

# application

# required so we can reach the nginx server from other containers via that hostname

# nginx

# workspace

The COMPOSE_ variables in the beginning set some reasonable defaults for docker-compose.

Building and running the containers

By now, we should have everything we need set up to get our dockerized PHP development up and running. If you haven't done it already, now would be a great time to clone the repository and checkout the part_3_structuring-the-docker-setup-for-php-projects branch:

git clone
cd docker-php-tutorial
git checkout part_3_structuring-the-docker-setup-for-php-projects

Now copy the .env.exmaple to .env. All the default values should work out of the box - unless you already have something running on port 80 or 443. In that case you have to change NGINX_HOST_HTTP_PORT / NGINX_HOST_HTTP_PORT to a free port.

cp .env.example .env

We can examine the "final" docker-compose.yml after the variable substitution via

docker-compose -f .docker/docker-compose.yml --project-directory .docker config
    driver: bridge
        APP_CODE_PATH: /var/www/current
        APP_GROUP: www-data
        APP_GROUP_ID: '1000'
        APP_USER: www-data
        APP_USER_ID: '1000'
        TZ: UTC
      context: D:\codebase\docker-php-tutorial\.docker
      dockerfile: ./nginx/Dockerfile
    image: php-docker-tutorial/nginx
        - docker-php-tutorial.local
    - published: 80
      target: 80
    - published: 443
      target: 443
    - /d/codebase/docker-php-tutorial:/var/www/current:rw
// ...

Note, that this command is run from ./docker-php-tutorial. If we would run this from ./docker-php-tutorial/.docker, we could simply use docker-compose config - but since we'll define that in a Makefile later anyway, the additional "verbosity" won't matter ;)

This command is also a great way to check the various paths that are resolved to their absolute form, e.g.

context: D:\codebase\docker-php-tutorial\.docker


- /d/codebase/docker-php-tutorial:/var/www/current:rw

The actual build is triggered via

docker-compose -f .docker/docker-compose.yml --project-directory .docker build --parallel

Since we have more than one container, it makes sense to build with --parallel.

To start the containers, we use

docker-compose -f .docker/docker-compose.yml --project-directory .docker up -d

and should see

$ docker-compose -f .docker/docker-compose.yml --project-directory .docker up -d
Starting docker-php-tutorial_nginx_1     ... done
Starting docker-php-tutorial_workspace_1 ... done
Starting docker-php-tutorial_php-fpm_1   ... done

Testing if everything works

After rewriting our own docker setup a couple of times, I've come to appreciate a structured way to test if "everything" works. Everything as in:

  • are all containers running?
  • does "host.docker.internal" exist?
  • do we see the correct output when sending a request to nginx/php-fpm?
  • are all required php extensions installed?

This might seem superfluous (after all, we just defined excatly that in the Dockerfiles), but there will come a time when you (or someone else) need to make changes (new PHP version, new extensions, etc.) and having something that runs automatically and informs you about obvious flaws is a real time saver.

You can see the full test file in the repository. Since my bash isn't the best, I try to keep it as simple as possible. The tests can be run via

sh .docker/

and should yield something like this:

Testing service 'workspace'
Checking if 'workspace' has a running container
Testing PHP version '7.3' on 'workspace' for 'php' and expect to see 'PHP 7.3'
Testing PHP module 'xdebug' on 'workspace' for 'php'
Testing PHP module 'Zend OPcache' on 'workspace' for 'php'
Checking 'host.docker.internal' on 'workspace'

Testing service 'php-fpm'

Makefile and .bashrc

In the previous sections I have introduced a couple of commands, e.g. for building and running containers. And to be honest, I find it kinda challenging to keep them in mind without having to look up the exact options and arguments. I would usually create a helper function or an alias in my local .bashrc file in a situation like that - but that wouldn't be available to other members of the team then and it would be very specific to this one project. Instead we'll provide a Makefile as a central reference point.

Using make as central entry point

Please refer to the repository for the full Makefile.

Going into the details of make is a little out of scope for this article, so I kindly refer to some articles that helped me get started:

Both are written with a PHP context in mind. Tip: If you are using PhpStorm, give the Makefile support plugin a try. And don't forget the number one rule: A Makefile requires tabs!

Note: If you are using Windows, make is probably not available. See Install make on Windows (MinGW) for instructions to set it up.

The Makefile ist located in the root of the application. Since we use a help target that makes the Makefile self-documenting, we can simply run make to see all the available commands:

$ make

  make <target>

[Docker] Build / Infrastructure
  docker-clean                 Remove the .env file for docker
  docker-init                  Make sure the .env file exists for docker
  docker-build-from-scratch    Build all docker images from scratch, without cache etc. Build a specific image by providing the service name via: make docker-build CONTAINER=<service>
  docker-build                 Build all docker images. Build a specific image by providing the service name via: make docker-build CONTAINER=<service>
  docker-up                    Start all docker containers. To only start one container, use CONTAINER=<service>
  docker-down                  Stop all docker containers. To only stop one container, use CONTAINER=<service>
  docker-test                  Run the infrastructure tests for the docker setup

As a new developer, your "onboarding" to get a running infrastructure should now look like this:

make docker-clean
make docker-init
make docker-build-from-scratch
make docker-test

Install make on Windows (MinGW)

make doesn't exist on Windows and is also not part of the standard installation of MinGW (click here to learn how to setup MinGW) Setting is up is straight forward but as with "everything UI" it's easier if you can actually "see what I'm doing" - so here's a video:

The steps are as follows:

Easy container access via din .bashrc helper

I've got one last goodie for working with Docker that I use all the time:

Logging into a running container via docker exec and the din / dshell helper.

Log into any running docker container via din helper

To make this work, put the following code in your .bashrc file

function din() {

  if [[ -n "$2" ]];
    user="--user $2"

  if [[ -n "$3" ]];

  if [[ "$(expr substr $(uname -s) 1 5)" == "MINGW" ]]; then
  ${prefix} docker exec -it ${user} $(docker ps --filter name=${filter} -q | head -1) ${shell}

The $(docker ps --filter name=${filter} -q | head -1) part will find partial matches on running containers for the first argument and pass the result to the docker exec command. In effect, we can log into any container by only providing a minimal matching string on the container name. E.g. to log in the workspace container I can now simply type din works from anywhere on my system.

Fundamentals on building the containers

Since we have now "seen" the end result, let's take a closer look behind the scenes. I assume that you are already somewhat familiar with Dockerfiles and have used docker-compose to orchestrate multiple services (if not, check out Persisting image changes with a Dockerfile and Putting it all together: Meet docker-compose). But there are some points I would like to cover in a little more detail.

Understanding build context

There are two essential parts when building a container:

  • the Dockerfile
  • the build context

You can read about the official description in the Dockerfile reference. You'll usually see something like this:

docker build .

which assumes that you use the current directory as build context and that there is a Dockerfile in the same directory.

But you can also start the build via

docker build .docker -f .docker/nginx/Dockerfile
                 |      |
                 |      └── use the Dockerfile at ".docker/nginx/Dockerfile"
                 └── use the .docker subdirectory as build context

For me, the gist is this: The build context defines the files and folders (recursively) on your machine that are send from the Docker CLI to the Docker Daemon that executes the build process of a container so that you can reference those files in the Dockerfile (e.g. via COPY). Take the following structure for example:

├── .docker/
    ├── .shared/
    |   └── scripts/
    |       └── ...
    └── nginx/
        ├── nginx.conf
        └── Dockerfile

Assume, that the current working directory is <project>/. If we started a build via

docker build .docker/nginx -f .docker/nginx/Dockerfile

the context would not include the .shared folder so we wouldn't be able to COPY the scripts/ subfolder. If we ran

docker build .docker -f .docker/nginx/Dockerfile

however, that would make the .shared folder available. In the Dockerfile itself, I need to know what the build context is, because I need to adjust the paths accordingly. Concrete example for the folder structure above and build triggered via docker build .docker -f .docker/nginx/Dockerfile:


# build context is .docker ...

# ... so the following COPY refers to .docker/.shared
COPY ./.shared /tmp

# ... so the following COPY refers to .docker/nginx/nginx.conf
COPY ./nginx/nginx.conf /tmp

The build context for all of our containers will be the .docker directory, so that all build processes have access to the .shared scripts and config. Yes, that also means that the php-fpm container has access to files that are only relevant to the mysql container (for instance), but the performance penalty is absolutely neglectable. Plus, as long as we don't actively COPY those irrelevant files, they won't bloat up our images.

A couple of notes:

  • I used to think that the build context is always tied to the location of the Dockerfile but that's only the default, it can be any directory
  • the build context is actually send to the build process - i.e. you should avoid unnecessary files / folders as this might affect performance, especially on big files (iaw: don't use / as context!)
  • similar to git, Docker knows the concept of a .dockerignore file to exclude files from being included in the build context

Dockerfile template

The Dockerfiles for the containers roughly follow the structure outlined below:

FROM ...

# path to the directory where the Dockerfile lives relative to the build context
ARG SERVICE_DIR="./service"

# get the scripts from the build context and make sure they are executable
COPY .shared/scripts/ /tmp/scripts/
RUN chmod +x -R /tmp/scripts/

# set timezone
RUN /tmp/scripts/ ${TZ}

# add users
ARG APP_USER=www-data


# install common software
RUN /tmp/scripts/

# perform any other, container specific build steps
COPY ${SERVICE_DIR}/config/* /etc/service/config
RUN /tmp/scripts/ /etc/service/config/default.conf \
    "__APP_USER" \
    "${APP_USER}" \
# [...]

# set default work directory

# cleanup 
RUN /tmp/scripts/

CMD [...]

The comments should suffice to give you an overview - so let's talk about the individual parts in detail.

Setting the timezone


Let's start with a simple and obvious one: Ensuring that all containers use the same system timezone (see here and here)


ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone

The script is then called from the Dockerfile via

RUN /tmp/scripts/ ${TZ}

Synchronizing file and folder ownership on shared volumes


Docker makes it really easy to share files between containers by using volumes. For simplicities sake, you can picture a volume simply as an additional disk that multiple containers have access to. And since it's PHP we're talking about here, sharing the same application files is a common requirement (e.g. for php-fpm, nginx, php-workers).

As long as you are only dealing with one container, life is easy: You can simply chown files to the correct user. But since the containers might have a different user setup, permissions/ownership becomes a problem. Checkout this video on Docker & File Permissions for a practical example in a Laravel application.

The first thing for me was understanding that file ownership does not depend on the user name but rather on the user id. And you might have guessed it: Two containers might have a user with the same name but with a different id. The same is true for groups, btw. You can check the id by running id <name>, e.g.

id www-data
uid=33(www-data) gid=33(www-data) groups=33(www-data)

File ownership with multiple containers using a shared volume

That's inconvenient but rather easy to solve in most cases, because we have full control over the containers and can assign ids as we like (using usermod -u <id> <name>) and thus making sure every container uses the same user names with the same user ids.

Things get complicated when the volume isn't just a Docker volume but a shared folder on the host. This is usually what we want for development, so that changes on the host are immediately reflected in all the containers.

File ownership with multiple containers using a shared volume from the host

This issue only affects users with a linux host system! Docker Desktop (previously known as Docker for Mac / Docker for Win) has a virtualization layer in between that will effectively erase all ownership settings and make everything shared from the host available to every user in a container.

We use the following script to ensure a consistent user setup when building a container:



new_user_id_exists=$(id ${APP_USER_ID} > /dev/null 2>&1; echo $?) 
if [ "$new_user_id_exists" = "0" ]; then
    (>&2 echo "ERROR: APP_USER_ID $APP_USER_ID already exists - Aborting!");
    exit 1;

new_group_id_exists=$(getent group ${APP_GROUP_ID} > /dev/null 2>&1; echo $?) 
if [ "$new_group_id_exists" = "0" ]; then
    (>&2 echo "ERROR: APP_GROUP_ID $APP_GROUP_ID already exists - Aborting!");
    exit 1;

old_user_id=$(id -u ${APP_USER})
old_user_exists=$(id -u ${APP_USER} > /dev/null 2>&1; echo $?) 
old_group_id=$(getent group ${APP_GROUP} | cut -d: -f3)
old_group_exists=$(getent group ${APP_GROUP} > /dev/null 2>&1; echo $?)

if [ "$old_group_id" != "${APP_GROUP_ID}" ]; then
    # create the group
    groupadd -f ${APP_GROUP}
    # and the correct id
    groupmod -g ${APP_GROUP_ID} ${APP_GROUP}
    if [ "$old_group_exists" = "0" ]; then
        # set the permissions of all "old" files and folder to the new group
        find / -group $old_group_id -exec chgrp -h ${APP_GROUP} {} \; || true

if [ "$old_user_id" != "${APP_USER_ID}" ]; then
    # create the user if it does not exist
    if [ "$old_user_exists" != "0" ]; then
        useradd ${APP_USER} -g ${APP_GROUP}

    # make sure the home directory exists with the correct permissions
    mkdir -p /home/${APP_USER} && chmod 755 /home/${APP_USER} && chown ${APP_USER}:${APP_GROUP} /home/${APP_USER} 

    # change the user id, set the home directory and make sure the user has a login shell
    usermod -u ${APP_USER_ID} -m -d /home/${APP_USER} ${APP_USER} -s $(which bash)

    if [ "$old_user_exists" = "0" ]; then
        # set the permissions of all "old" files and folder to the new user 
        find / -user $old_user_id -exec chown -h ${APP_USER} {} \; || true

The script is then called from the Dockerfile via

ARG APP_USER=www-data


The default values can be overriden by passing in the corresponding build args.

Linux users should use the user id of the user on their host system - for Docker Desktop users the defaults are fine.

Modifying configuration files

For most services we probably need some custom configuration settings, like

  • setting php.ini values
  • changing the default user of a service
  • changing the location of logfiles

There are a couple of
common approaches to modify application configuration in docker and we are currently trying to stick to two rules:

  1. provide additional files that override defaults if possible
  2. change non-static values with a simple search and replace via sed during the container build

Providing additional config files

Most services allow the specification of additional configuration files that override the default values in a default config file. This is great because we only need to define the settings that we actually care about instead of copying a full file with lots of redundant values.

Take the php.ini file for example: It allows to places additional .ini files in a specific directory that override the default values. An easy way to find this directory is php -i | grep "additional .ini":

$ php -i | grep "additional .ini"
Scan this dir for additional .ini files => /usr/local/etc/php/conf.d

So instead of providing a "full" php.ini file, we will use a zz-app.ini file instead, that only contains the .ini settings we actually want to change and place it under /usr/local/etc/php/conf.d.

Why zz-? Because

[...] Within each directory, PHP will scan all files ending in .ini in alphabetical order.

so if we want to ensure that our .ini files comes last (overriding all previous settings), we'll give it a corresponding prefix :)

The full process would look like this:

  • place the file in the .docker folder, e.g. at .docker/.shared/config/php/conf.d/zz-app.ini
  • pass the folder as build context
  • in the Dockerfile, use COPY .shared/config/php/conf.d/zz-app.ini /usr/local/etc/php/conf.d/zz-app.ini

Changing non-static values


Some configuration values are subject to local settings and thus should not be hard coded in configuration files. Take the memory_limit configuration for php-fpm as an example: Maybe someone in the team can only dedicate a limited amount of memory to docker, so the memory_limit has to be kept lower than usual.

We'll account for that fact by using a variable prefixed by __ instead of the real value and replace it with a dynamic argument in the Dockerfile. Example for the aforementioned zz-app.ini:

memory_limit = __MEMORY_LIMIT

We use the following script to replace the value:



sed -i -e "s#${VAR_NAME}#${VAR_VALUE}#" "${CONFIG_FILE}"

The script is then called from the Dockerfile via


RUN /tmp/scripts/ \
    "/usr/local/etc/php/conf.d/zz-app.ini" \
    "__MEMORY_LIMIT" \

where PHP_FPM_MEMORY_LIMIT has a default value of 1024M but can be overriden when the actual build is initiated.

Installing php extensions


When php extensions are missing, googling will often point to answers for normal linux systems using apt-get or yum, e.g. sudo apt-get install php-xdebug. But for the official docker images, the recommended way is using the docker-php-ext-configure, docker-php-ext-install, and docker-php-ext-enable helper scripts. Unfortunately, some extensions have rather complicated dependencies, so that the installation fails. Fortunately, there is a great project on Github called docker-php-extension-installer that takes care of that for us and is super easy to use:

FROM php:7.3-cli

ADD /usr/local/bin/

RUN chmod uga+x /usr/local/bin/install-php-extensions && sync && install-php-extensions xdebug

The readme also contains an overview of supported extension per PHP version. To ensure that all of our PHP containers have the same extensions, we provide the following script:


# add wget
apt-get update -yqq && apt-get -f install -yyq wget

# download helper script
wget -q -O /usr/local/bin/install-php-extensions \
    || (echo "Failed while downloading php extension installer!"; exit 1)

# install all required extensions
chmod uga+x /usr/local/bin/install-php-extensions && sync && install-php-extensions \
    xdebug \
    opcache \

If you're not sure which extensions are required by your application, give the ComposerRequireChecker a try.

Installing common software


There is a certain set of software that I want to have readily available in every container. Since this a development setup, I'd prioritize ease of use / debug over performance / image size, so this might seem like a little "too much". I think I'm also kinda spoiled by my Homestead past, because it's so damn convenient to have everything right at your fingertips :)

Anyway, the script is straight forward:


apt-get update -yqq && apt-get install -yqq \
    curl \
    dnsutils \
    gdb \
    git \
    htop \
    iputils-ping \
    iproute2 \
    ltrace \
    make \
    procps \
    strace \
    sudo \
    sysstat \
    unzip \
    vim \
    wget \


  • this list should match your own set of go-to tools. I'm fairly open to adding new stuff here if it speeds up the dev workflow. But if you don't require some of the tools, get rid of them.
  • sorting the software alphabetically is a good practice to avoid unnecessary duplicates. Don't do this by hand, though! If you're using an IDE / established text editor, chances are high that this is either a build-in functionality or there's a plugin available. I'm using Lines Sorter for PhpStorm

Cleaning up


Nice and simple:


apt-get clean
rm -rf /var/lib/apt/lists/* \
       /tmp/* \
       /var/tmp/* \
       /var/log/lastlog \

Using ENTRYPOINT for pre-run configuration

Docker went back to the unix roots with the do on thing and do it well philosophy which is manifested in the CMD and ENTRYPOINT instructions.

As I had a hard time understanding those instructions when I started with Docker, here's my take at a layman's terms description:

  • since a container should do one thing, we need to specify that thing. That's what we do with ENTRYPOINT. Concrete examples:
    • a mysql container should probably run the mysqld daemon
    • a php-fpm container.. well, php-fpm
  • the CMD is passed as the default argument to the ENTRYPOINT
  • the ENTRYPOINT is executed every time we run a container. Some things can't be done during build but only at runtime (e.g. find the IP of the host from within a container - see section Providing host.docker.internal for linux host systems ) - ENTRYPOINT is a good solution for that problem
  • technically, we can only override an already existing ENTRYPOINT from the base image. But: We can structure the new ENTRYPOINT like a decorator by adding exec "[email protected]" at the end to simulate inheritance from the parent image

To expand on the last point, consider the default ENTRYPOINT of the current [2019-02-23; PHP 7.3] php-fpm image


set -e

# first arg is `-f` or `--some-option`
if [ "${1#-}" != "$1" ]; then
    set -- php-fpm "[email protected]"

exec "[email protected]"

In the corresponding Dockerfile we find the following instructions:

# [...]
ENTRYPOINT ["docker-php-entrypoint"]
# [...]
CMD ["php-fpm"]

That means: When we run the container it will pass the string "php-fpm" to the ENTRYPOINT script docker-php-entrypoint as argument which will then execute it (due to the exec "[email protected]" instruction at the end):

$ docker run --name test --rm php:fpm
[23-Feb-2019 14:49:20] NOTICE: fpm is running, pid 1
[23-Feb-2019 14:49:20] NOTICE: ready to handle connections
# php-fpm is running
# Hit ctrl + c to close the connection
$ docker stop test

We could now override the default CMD "php-fpm" with something else, e.g. a simple echo "hello". The ENTRYPOINT will happily execute it:

$ docker run --name test --rm php:fpm echo "hello"

But now the php-fpm process isn't started any more. How can we echo "hello" but still keep the fpm process running? By adding our own ENTRYPOINT script:

echo 'hello'

exec "[email protected]"

Full example (using stdin to pass the Dockerfile via Heredoc string)

$ docker build -t my-fpm -<<'EOF'
FROM php:fpm

RUN  touch "/usr/bin/" \
  && echo "#!/bin/sh" >> "/usr/bin/" \
  && echo "echo 'hello'" >> "/usr/bin/" \
  && echo "exec \"\[email protected]\"" >> "/usr/bin/" \
  && chmod +x "/usr/bin/" \
  && cat "/usr/bin/" \

ENTRYPOINT ["/usr/bin/", "docker-php-entrypoint"]
CMD ["php-fpm"]

Note that we added the ENTRYPOINT of the parent image docker-php-entrypoint as argument to our own ENTRYPOINT script /usr/bin/ so that we don't loose its functionality. And we need to define the CMD instruction explicitly, because the one from the parent image is automatically removed once we define our own ENTRYPOINT.

But: It works:

$ docker run --name test --rm my-fpm
[23-Feb-2019 15:43:25] NOTICE: fpm is running, pid 1
[23-Feb-2019 15:43:25] NOTICE: ready to handle connections
# Hit ctrl + c to close the connection
$ docker stop test

Providing host.docker.internal for linux host systems

Script: docker-entrypoint/

In the previous part of this tutorial series, I explained how to build the Docker container in a way that it plays nice with PhpStorm and Xdebug. The key parts were SSH access and the magical host.docker.internal DNS entry. This works great for Docker Desktop (Windows and Mac) but not for Linux. The DNS entry doesn't exist there. Since we rely on that entry to make debugging possible, we will set it "manually" if the host doesn't exist with the following script (inspired by the article Access host from a docker container):


set -e


# check if the host exists - this will fail on linux
if dig ${HOST_DOMAIN} | grep -q 'NXDOMAIN'
  # resolve the host IP
  HOST_IP=$(ip route | awk 'NR==1 {print $3}')
  # and write it to the hosts file
  echo "$HOST_IP\t$HOST_DOMAIN" >> /etc/hosts

exec "[email protected]"

The script is placed at .shared/docker-entrypoint/ and added as ENTRYPOINT in the Dockerfile via

COPY .shared/scripts/ /tmp/scripts/

RUN mkdir -p /bin/docker-entrypoint/ \
 && cp /tmp/scripts/docker-entrypoint/* /bin/docker-entrypoint/ \
 && chmod +x -R /bin/docker-entrypoint/ \

ENTRYPOINT ["/bin/docker-entrypoint/", ...]


  • since this script depends on runtime configuration, we need to run it as an ENTRYPOINT
  • there is no need to explicitly check for the OS type - we simply make sure that the DNS entry exists and add it if it doesn't
  • we're using dig (package dnsutils) and ip (package iproute2) which need to be installed during the build time of the container. Tip: If you need to figure out the package for a specific command, give a try. See the entry for dig for instance.
  • this workaround is only required in containers we want to debug via xdebug

Wrapping up

Congratulations, you made it! If some things are not completely clear by now, don't hesitate to leave a comment. Apart from that, you should now have a running docker setup for your local PHP development as well as a nice "flow" to get started each day.

In the next part of this tutorial, we will add some more containers (php workers, mysql, redis, blackfire) and use a fresh installation of Laravel to make use of them.

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