Symfony 4 is painfully slow in DEV

It seems that changing the consistency level greatly increases Symfony performance. (see Docker docs)

Here is my new docker-compose.yml file. Note the ":cached" after the volumne.

version: '3'
services:
  web:
    image: apache-php7
    ports:
     - "80:80"
    volumes:
      - .:/app:cached
    tty: true

Note from manual:

For directories mounted with cached, the host’s view of the file system is authoritative; writes performed by containers are immediately visible to the host, but there may be a delay before writes performed on the host are visible within containers.

Since the provided answer is working with macOSX, only, but performance issues exist with Docker for Windows as well the preferred answer didn't help in my case. I was following different approach partially described in answers to similar questions here on SO.

According to Performance Best Practices folders with heavy load such as vendor and var in a Symfony application shouldn't be part of a shared mount. If you require to persist those folders you should use volumes instead.

To prevent interferences with shared volume in /app I was relocating those two folders to separate folder /symfony in container. In Dockerfile folders /symfony/var and /symfony/vendor are created in addition.

The script run on start of container is setting symbolic links from /app/var to /symfony/var and from /app/vendor to /symfony/vendor. These two new folders are then mounted to volumes e.g. in a docker-compose.yml file.

Here is what I was adding to my Dockerfile:

RUN mkdir /app && mkdir /symfony/{var,vendor}

COPY setup-symfony.sh /setup-symfony.sh

VOLUME /symfony/var
VOLUME /symfony/vendor

Here is what I was adding to my startup script right before invoking composer update or any task via bin/console:

[ -e /app/var ] || ln -s /symfony/var /app/var
[ -e /app/vendor ] || ln -s /symfony/vendor /app/vendor

This is what my composition looks like eventually:

version: "3.5"
services:
  database:
    build:
      context: docker/mysql
    volumes:
      - "dbdata:/var/lib/mysql"
    environment:
      MYSQL_ALLOW_EMPTY_PASSWORD: 1

  application:
    depends_on:
      - database
    build:
      context: docker/lamps
    ports:
      - "8000:8000"
    volumes:
      - ".:/app:cached"
      - "var:/symfony/var"
      - "vendor:/symfony/vendor"
    environment:
      DATABASE_URL: mysql://dbuser:dbuser@database/dbname

volumes:
  dbdata:
  var:
  vendor:

Using this setup Symfony is responding within 500ms rather than taking 4000ms and more.

UPDATE: When using an IDE for developing Symfony-based application like PhpStorm you might need the files in vendor/ for code assist or similar. In my case I was able to take a snapshot of those files and put them into a different folder which is shared with host as well, but isn't actively used by Symfony/PSR, e.g. vendor.dis/. This snapshot is taken manually once per install/upgrade e.g. by entering the running container with a shell like so:

docker exec -it IDofContainer /bin/sh

Then in shell invoke

cp -Lr vendor vendor.dis

Maybe you have to fix the pathnames or make sure to switch into folder containing the your app first.

In my case using PhpStorm the vendor.dis/ was picked up by background indexing and obeyed by code inspection and code assist. Visual Studio code was having issues with the great number of untracked changes with regards to git so I had to explicitly make this snapshot ignored by git, adding its name in .gitignore file.

UPDATE 2020: More recent setups may have issues with accessing folders like /symfony/templates or /symfony/public e.g. on warming up the cache. This is obviously due to using relative folders in auto-loading code now existing in /symfony/vendor due to relocation described above. As an option, you could directly mount extra volumes in /app/var and /app/vendor instead of /symfony/var and /symfony/vendor. Creating deep copies of those folders in /app/var.dis and /app/vendor.dis keeps enabling code assist and inspections in host filesystem.

1. do not sync the vendor folder

---

In your docker file, you can prevent the vendor folder to sync with the container. This has the biggest impact on performance because the folder gets very huge:

#DockerFile:

  volumes:
    - /local/app:/var/www/html/app
    - /var/www/html/app/vendor # ignore vendor folder

This will have the effect that you will need to copy the vendor folder manuelly to the container once after the build and when you update your composer dependencies:

docker cp  /local/app/vendor <CONTAINER_ID>:/var/www/html/app/

2. do not sync the cache folder

---

in your src/Kernel.php:

public function getCacheDir()
{
    // for docker performance
    if ($this->getEnvironment() === 'test' || $this->getEnvironment() === 'dev') {
        return '/tmp/'.$this->environment;
    } else {
        return $this->getProjectDir().'/var/cache/'.$this->environment;
    }

}

3. sync the app folders in cached mode

---

use cached mode for volume mounts on development environments: http://docs.docker.oeynet.com/docker-for-mac/osxfs-caching/#delegated

The cached configuration provides all the guarantees of the delegated configuration, and some additional guarantees around the visibility of writes performed by containers. As such, cached typically improves the performance of read-heavy workloads, at the cost of some temporary inconsistency between the host and the container.

For directories mounted with cached, the host’s view of the file system is authoritative; writes performed by containers are immediately visible to the host, but there may be a delay before writes performed on the host are visible within containers.

This makes sense for dev envrionemtns, because normally you change your code with your IDE on the host not in the container and sync into the container. #DockerFile:

  volumes:
    - /local/app:/var/www/html/app:cached

4. disable Docker debug mode

---

check if Docker is NOT in debug mode:

docker info
# It Should display: Debug Mode: false

Disable in docker-config:

{
  
  "debug": false,
} 

5. do not use a file cache

---

this is extra slow in a docker box, use for examle a SQLITE cache: Symfony Sqlite Cache

6. for Windows 10 users: Use Docker Desktop with WSL 2 support

---

Use Docker Desktop with WSL 2 support, whichs incredibley boosts performance in general:

https://docs.docker.com/docker-for-windows/wsl/