Running flash player on Docker containers

5 min readJan 4, 2021

Prologue and motivation

As most of you are aware Adobe Flash has reached end of life and is no longer enabled on major browsers. This makes me sad because I have fond memories of flash animations and games that were all over the web in my early days. There are already several initiatives to allow for these old files to continue running in modern era from a standalone catalog and player with over 70,000 games to a full-fledged flash emulator written in Rust.

Recently I did a Docker course and since I am a firm believer in learning by doing I wanted a very small project as a kind of exercise. So I decided to see if it is possible to wrap a flash player inside a docker container. Then anyone can run flash animations because all the dependencies will be neatly packaged inside a docker image. At least that is the pitch.

This would be a good exercise, but in reality it is more fun than practical. After all a standlone flash player can still be installed on a machine even if it does not come by default in the browser. So if someone really needed a flash player, a manual install is way simpler than setting up a docker container. The only practical use would be to enable old flash animations or games inside a browser or other clients with minimal hustle for end users such as installing third party plugins or programs. This would probably be rather expensive and in breach of Adobe licensing, but heck not everything that we built must have a practical use case.

Goal

🏁Run a flash animation inside a docker container and stream the video to a remote client.

In this blog post, I will document the process I went through and what I learned. Along the way I will do my best to explain the relevant docker concepts. Let’s get started.

Prerequisites

First things first, we will need to get docker. The easiest way to install docker on Windows is to download and install docker desktop. This requires Hyper-V which unfortunately does not come with all Windows 10 distributions so make sure to check for that.

Next, we will need some kind of video streaming client. There are two easy options vnc and x11. The latter seemed easier to set up on Windows. It is a single executable that can be installed with choco install vcxsrv. For a complete step-by-step guide please refer to this tutorial.

Dockerfile

With all the prerequisites in place it is time to get to work on the Dockerfile. This is a special file format that contains instructions for docker about how to prepare an image file. The image file is essentially an executable that contains the app that you are trying to run (e.g. flash player) along with all dependencies it needs. Once we have the image it can be run inside a container.

To keep it simple I am going to use ubuntu 18 as a base image. This greatly simplifies the setup because ubuntu comes with a ton of preinstalled dependencies and a package manager that lets us easily install more packages as needed.

In order to get the standalone flash running we need only a few things:

install any flash player library dependencies
download and unzip flash player
start flash player with a specific swf file that is either hosted or copied to the container
point flash player to output to the remote display

The resulting docker file is straightforward enough. My only issue was figuring out the list of dependencies. Unfortunately flash player did not provide this list (at least I was not able to find it). After some googling and failed attempts I ended up just trying to run the docker container and adding the missing libraries one by one as they were reported. Luckily there were only a few of these dependencies, but it was still a bit cumbersome.

FROM ubuntu:18.04RUN apt-get update # flash dependencies
RUN apt-get install -y libglu1 libxcursor1 libnss3 libgtk2.0-0  # download and extract flash player
WORKDIR /usr/local/flash
RUN apt-get install -y curl && .\
    curl -O https://fpdownload.macromedia.com/pub/flashplayer/updaters/32/flash_player_sa_linux.x86_64.tar.gz 
RUN tar zxvf flash_player_sa_linux.x86_64.tar.gz  # copy over a sample swf file for a quick demo 
COPY ./wheel.swf wheel.swf   # start the flash player with the demo swf file 
CMD /usr/local/flash/flashplayer wheel.swf

Building and running the container

I used the standard build command to build an image from the above docker file:

docker build -t flash .

For those new to docker, this command is essentially saying to docker to build an image from the dockerfile above and give it a tag flash, which we can use later to refer to the image.

Next, the tricky part is connecting the GUI from docker to my local Windows machine. Luckily this is made easy with VcXsrv which we installed previously, as it does most of the heavy lifting. All we need to do is point the docker container to our VcXsrv instance using our host IP. The below command has my current host IP address, make sure to change that with your IP (use ipconfig)

docker run --rm -e DISPLAY=192.168.178.108:0.0 flash

This command tells docker to run the image tagged flash and point the display to the VcXsrv running on the host OS. The flag --rm is there to make sure that the container is removed as soon as we close the flash player dialog on the host OS so resource are not used unnecessarily.

And the outcome is this nice flash animation, streamed from a linux docker container to my Windows machine. Hooray 🎉

Wrap up

Before wrapping up, I want to point out two caveats that I learned about after completing this. The first one is that the flash animation has a picture, but no sound. This requires more setup and another application called PulseAudio. A sample dockerfile can be found here.

Another caveat is that supposedly the linux package of the flash player is less stable and more error-prone than the windows one. So if you are really considering using this for any kind of serious project I highly recommend switching to a Windows container. Unfortunately I only found out about this after I finished this exercise, so it makes little sense to go back right now and redo everything. Perhaps one day in the future.

I hope this post helps you on your journey with Docker, it certainly was a lot of fun to implement it.

All sources are on GitHub: https://github.com/gajduk/docker-flash

Originally published at https://www.notion.so.