This post is going to introduce a setup for domjudge with docker

Note: All the information is coming from domjudge.org

All tests running on Windows 11 WSL2 Ubuntu 22.04 LTS

Running Domjudge on local machine

Install docker

for pkg in docker.io docker-doc docker-compose podman-docker containerd runc; do sudo apt-get remove $pkg; done
sudo apt update
sudo apt install ca-certificates curl gnupg
sudo install -m 0755 -d /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
sudo chmod a+r /etc/apt/keyrings/docker.gpg
echo \
  "deb [arch="$(dpkg --print-architecture)" signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
  "$(. /etc/os-release && echo "$VERSION_CODENAME")" stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt update
sudo apt install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin
sudo docker run hello-world

Install domjudge docker image

sudo docker pull domjudge/domserver
sudo docker pull domjudge/judgehost

Before starting the containers, make sure you have a MySQL / MariaDB database somewhere:

sudo docker pull mariadb

MariaDB container

The easiest way to get one up and running is to use the MariaDB Docker container:

sudo docker run -it --name dj-mariadb -e MYSQL_ROOT_PASSWORD=rootpw -e MYSQL_USER=domjudge -e MYSQL_PASSWORD=djpw -e MYSQL_DATABASE=domjudge -p 13306:3306 mariadb --max-connections=1000

This will start a MariaDB container, set the root password to rootpw, create a MySQL user named domjudge with password djpw and create an empty database named domjudge. It will also expose the server on port 13306 on your local machine, so you can use your favorite MySQL GUI to connect to it. If you want to save the MySQL data after removing the container, please read the MariaDB Docker Hub page for more information.

DOMserver container

If you are on Linux make sure you have cgroups enabled. See the DOMjudge documentation about setting up a judgehost for information about how to do this. Docker on Windows and macOS actually use a small Linux VM which already has these options set.

Run the domserver using the following command:

sudo docker run --link dj-mariadb:mariadb -it -e MYSQL_HOST=mariadb -e MYSQL_USER=domjudge -e MYSQL_DATABASE=domjudge -e MYSQL_PASSWORD=djpw -e MYSQL_ROOT_PASSWORD=rootpw -p 12345:80 --name domserver domjudge/domserver:latest

If a specific DOMjudge version is required instead of the ‘latest’, replace ‘latest’ with the DOMjudge version (e.g. ‘5.3.0’).

The above command will start the container and set up the database. It will then start nginx and PHP-FPM using supervisord.

The initial passwords for the admin and judgehost users should be printed when starting the domserver, but if not, you can use the following commands to retrieve them:

sudo docker exec -it domserver cat /opt/domjudge/domserver/etc/initial_admin_password.secret
sudo docker exec -it domserver cat /opt/domjudge/domserver/etc/restapi.secret

You can now access the web interface on http://localhost:12345/ and log in as admin.

If you lose access to the admin user, see the DOMjudge documentation on resetting the password.

Make a note of the password for the judgehost user, it will be used when the judgehost container is configured. The password can be changed from the web interface by editing the judgehost user.

Judgehost container

To run a single judgehost, run the following command:

sudo docker run -it --privileged -v /sys/fs/cgroup:/sys/fs/cgroup:ro --name judgehost-0 --link domserver:domserver --hostname judgedaemon-0 -e JUDGEDAEMON_PASSWORD=jwcrulWzmX6PWfdKKmi06c6RntOd5vFS -e DAEMON_ID=0 domjudge/judgehost:latest

Again, replace latest with a specific version if desired. Make sure the version matches the version of the domserver.

This will start up a judgehost that is locked to the first CPU core of your machine.

If the judgedaemon stops for whatever reason, you should be able to see the error it produced in the shell where you started the judgehost. If you want to restart the judgehost, run ‘docker start judgehost-0’, where ‘judgehost-0’ is the value you passed to ‘–name’ in the ‘docker run’ command.

PS: make sure set the JUDGEDAEMON_PASSWORD parameter using the displayed judgehost password on the judgeserver startup terminal.

Docker compose

Or, one could use docker-compose command to read yml files to setup all the database, judgeserver, judgehost at once:

sudo docker-compose -f docker_compose.yml up -d

Test at local using the hello world problem

!!!! Now, the most excited remote judgehost setup !!!!

Say, there are two PC A and B, with IP address 192.168.137.2 (A) and 192.168.137.1 (B), and A is going to be the domserver while B is going to be the judgehost.

Firstly, install mariadb and domserver on PC A.

The key thing is, once the domserver container is running, execute the bash on domserver container:

sudo docker exec -it domserver /bin/bash

In the container, modified the configuration of web API URL in “restapi.secret” from its default to “http://192.168.137.2:12345/api”:

apt-get update
apt-get install vim
vim /opt/domjudge/domserver/etc/restapi.secret

This will allow the judgehost to access remote from the same networ range in 192.168.137.*.

Secondly, install judgehost on PC B

Instead of create judgehost container at local, use the modified web API URL to create the container associate to the remote domserver:

sudo docker run -it --privileged -v /sys/fs/cgroup:/sys/fs/cgroup:ro --name judgehost-1 --hostname judgedaemon-1 -e DAEMON_ID=0 -e DOMSERVER_BASEURL='http://192.168.137.2:12345/' -e JUDGEDAEMON_USERNAME='judgehost' -e JUDGEDAEMON_PASSWORD='uCp9VCj5fLUG4CEKtPjDQaVnHF9A1V08' domjudge/judgehost:latest

This will create a judgehost container at PC B that could be used for calling from PC A.

Now we could submit through the “demo” user and as shown it can successfully found PC B as judgehost to do the judge of submision.

If there are any large data needed for the contest and you don’t want to copy it into the ‘chroot’ environment inside the container, one could mount it to the container using the absolute directory matching it in the container when creating it.

e.g. all the files in the ‘/chroot/domjudge/data’ at local will be visible to the container at the same place with both read and write authentication:

docker run -it --privileged -v /chroot/domjudge/data:/chroot/domjudge/data:rw  -v /sys/fs/cgroup:/sys/fs/cgroup:ro --name judgehost-3 --hostname judgedaemon-3 -e DAEMON_ID=3 -e DOMSERVER_BASEURL='http://192.168.137.2:12345/' -e JUDGEDAEMON_USERNAME='judgehost' -e JUDGEDAEMON_PASSWORD='uCp9VCj5fLUG4CEKtPjDQaVnHF9A1V08' domjudge/judgehost:latest

Issues

1. Judgehost hangs after a successful java problem judgement

Judgehost is trying to execute one of its function called “evict” after a successful judgement and cannot do another further judgement. On the domserver, it shows the judgehost is down. But in the judgehost machine, it shows the docker is still running.

By looking into the source code of “evict”, it basically checks mounted folders and files and but seems there are chances to trigger infinite loop iterations.

By killing the executing “evict” process from the docker linux system, the judgehost can be back to normal again.

The temperal solution so far is to locate the workdir of judgehost and disable the “evict” function through the php script.

2. Large file sharing through docker

Large file can be shared by mounting local host folder into the ‘/chroot/domjudge’ which is the chroot directory for the domjudge. However, the actually validator is actually using the ‘/’ as the root direcotry while the judement will create its own working directory that mapping specific directories from the chroot.

So two changes have to be done:

a. create a symbolic link of the mounted folder to the actual root directory in the docker container :

For exampmle:

ln -s /chroot/domjudge/data /data

b. change the chroot-startstop.sh that allows the judgehost automatically mount the data folder under the chroot to its work directory

… SUBDIRMOUNTS=”etc usr lib bin” –> SUBDIRMOUNTS=”etc usr lib bin data” …

3. Memory limit issue

Sometimes the problem require very large memory to execute. There is a “Judging” menu in the “Configuration settings” on the web API. Change the “Memory limit: XXX “ to the value that meet the memory requirement which will help the judgehost to proceed the problem executions.

4. Unsupported commands

Sometimes the judgehost does not have the command as needed for the contest, e.g. unzip. This could be solved enter the docker shell by

docker exec -it <dockername> bash 

then use the chroot to locate the root directory in the docker and install the commands by (e.g. unzip)

chroot /chroot/domjudge && apt install unzip -y && exit

then restart the docker

docker stop <dockername> && docker start <dockername>