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Minecraft server hosting

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Gamocosm makes it easy to run cloud Minecraft servers.
Digital Ocean is used as the backend/hosting service, due to cost, reliability, and accessibility.
Gamocosm works well for friends who play together, but not 24/7.
Running a server 14 hours a week (2 hours every day) may cost 40 cents a month, instead of $5.

This README is directed towards developers; if you are a user looking for more information, please check out the wiki or drop by Gitter chat.

Minecraft Server Wrapper

The Minecraft Server Wrapper (for lack of a better name) is a light python webserver.
It provides an HTTP API for starting and stopping Minecraft servers, downloading the world, etc.
Please check it out and help improve it too!

Gamocosm Minecraft Flavours

The gamocosm-minecraft-flavours repository includes the setup scripts used to install different flavours of Minecraft on a new server.
Read this wiki page for adding support for new flavours, or manually installing something yourself.


Pull requests are welcome!

Setting Up Your Development Environment

You should have a Unix/Linux system.
The following instructions were made for Fedora 36 Server, but the steps should be similar on other distributions.
As of 2022 August 28, deployment and CI have been changed to use containers.
For development, containers are more convenient for the PostgreSQL and Redis processes,
but it is still recommended to run the development Rails and Sidekiq server "locally".

  1. Install dependencies to build ruby: (sudo) dnf install openssl-devel perl zlib-devel.
  2. Install rbenv and ruby-build. Read their docs for up to date instructions. But as of 2022 August 28:
    • Run git clone https://github.com/rbenv/rbenv.git ~/.rbenv.
    • Add $HOME/.rbenv/bin to your $PATH, usually done in ~/.bashrc. On recent versions of Fedora, ~/.bashrc sources any files in the directory ~/.bashrc.d (if it exists), so you don't have to edit .bashrc directly. (To create the directory, run mkdir ~/.bashrc.d.) For example, run echo 'PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc.d/rbenv (you can replace ~/.bashrc.d/rbenv with ~/.bashrc to modify .bashrc directly).
    • Additionally, add eval "$(rbenv init - bash)" to your shell: echo 'eval "$(rbenv init - bash)"' >> ~/.bashrc.d/rbenv (again, you may choose to modify .bashrc directly).
    • Restart (close and reopen) your shell for the changes to take effect.
    • Create the plugins directory for rbenv: mkdir ~/.rbenv/plugins.
    • Get ruby-build: git clone https://github.com/rbenv/ruby-build.git ~/.rbenv/plugins/ruby-build.
    • Check that ruby-build has been installed correctly: rbenv install --list.
  3. Install Ruby 3.1.2: rbenv install inside this project root directory (it reads .ruby-version).
  4. Check that ruby -v inside this project gives you version 3.1.2.
  5. Install dependencies to build gems: (sudo) dnf install libpq-devel.
  6. Install gem dependencies: bundle install.
  7. Generate or link your SSH keys; Gamocosm expects an id_gamocosm private key and an id_gamocosm.pub public key in the project root. Gamocosm uses this to connect to and set up the servers it creates. Gamocosm officially only supports ed25519 keys; somewhere down the stack, rsa keys are not supported (ed25519 keys are considered more secure):
    • To generate new keys, run: ssh-keygen -t ed25519. The default path saves to ~/.ssh/id_ed25519. If you leave it here, SSH will automatically try this key when SSHing (e.g. if you need to debug a Digital Ocean droplet created by your Gamocosm). Careful not to overwrite if you already have an existing ~/.ssh/id_ed25519 key!
    • To link a key ~/.ssh/id_ed25519, run ln -s ~/.ssh/id_ed25519 id_gamocosm, and similarly for the corresponding public key (with .pub extension).
      • If you plan on running Gamocosm in a container, note that podman/docker cannot copy symlinks; use cp to copy the files instead.
    • id_gamocosm and id_gamocosm.pub are ignored in Gamocosm's .gitignore so you don't have to worry about accidentally committing them.
  8. Create your environment file: cp template.env gamocosm.env.
  9. Make your environment file only readable (and writable) by the file owner (you): chown 600 gamocosm.env
  10. Update the config in gamocosm.env. See below for documentation.
    • In particular, if you are following these instructions to setup a development environment, you will want to change DATABASE_HOST and SIDEKIQ_REDIS_HOST both to localhost.
  11. Load environment variables: source load_env.sh. You will also need to do this in every new shell you run ruby/rails in.
  12. Install podman (or docker): (sudo) dnf install podman.
  13. Create the database container: podman create --name gamocosm-database --env "POSTGRES_USER=$DATABASE_USER" --env "POSTGRES_PASSWORD=$DATABASE_PASSWORD" --publish docker.io/postgres:14.5.
  14. Create the Redis container for Sidekiq: podman create --name gamocosm-sidekiq-redis --publish docker.io/redis:7.0.4.
  15. Start the containers: podman start gamocosm-database gamocosm-sidekiq-redis.
  16. Setup the database: bundle exec rails db:setup.
  17. Start the server: bundle exec rails s.
  18. Start the Sidekiq worker: bundle exec sidekiq.
  19. Optional: open the console: bundle exec rails c.

Environment File

  • DATABASE_HOST: May be a directory (for a Unix domain socket), or an IP/hostname (for a TCP connection). See below for more information.
  • DATABASE_PORT: Required even for Unix domain sockets. The default should work on Fedora provided you didn't change the postgresql settings.
  • DIGITAL_OCEAN_API_KEY: Your Digital Ocean API token.
  • DIGITAL_OCEAN_SSH_PRIVATE_KEY_PASSPHRASE: You should have generated or linked an id_gamocosm SSH key in the project root, with an (optional) passphrase.
  • SIDEKIQ_REDIS_HOST: You can leave this as the default.
  • SIDEKIQ_REDIS_PORT: You can leave this as the default.
  • SIDEKIQ_ADMIN_USERNAME: HTTP basic auth for Sidekiq web interface.
  • CLOUDFLARE_ZONE: Shown on the bottom right of CloudFlare's control panel for the domain.
  • DEVISE_SECRET_KEY: Only test, production.
  • MAIL_SERVER_*: See action mailer configuration in the Rails guide.
  • CACHE_REDIS_HOST: Caching for production. Is disabled/not used in development and test environments (see config/environments/development.rb and config/environments/test.rb).
  • CACHE_REDIS_PORT: See previous.
  • SECRET_KEY_BASE: Only production.
  • DEVELOPER_EMAILS: Comma separated list of emails to send exceptions to.
  • BADNESS_SECRET: Secret to protect /badness endpoint.

Database configuration

Database configuration is greatly simplified if you use a container image as described above.
However, the following information remains for reference, if you want to run PostgreSQL directly on your system.

Locate your postgres data directory.
On Fedora this is /var/lib/pgsql/data/.


Locate postgresql.conf in your postgres data directory.
The convention is that commented out settings represent the default values.
For a Unix domain socket connection, DATABASE_HOST should be one of the values of unix_socket_directories.
In general, the default is /tmp.
On Fedora, the default includes both /tmp and /var/run/postgresql.
For a TCP connection, DATABASE_HOST should be one of the values of listen_addresses (default localhost).
The value localhost should work if you're running postgresql locally.
Your DATABASE_PORT should be the value of port in this file (default 5432).

You can read more about connecting to postgresql at postgresql's docs.


Locate pg_hba.conf in your postgres data directory.
This file tells postgresql how to authenticate users. Read about it on the PostgreSQL docs.
The Rails config config/database.yml reads from the environment variables which you should have set in and loaded from gamocosm.env via source load_env.sh.
The postgres user you use must be a postgres superuser, as rails needs to enable the uuid extension.
To create a postgres user "gamocosm":

  • Switch to the postgres user: (sudo) su --login postgres.
  • Run createuser --createdb --pwprompt --superuser gamocosm (createuser --help for more info).

Depending on what method you want to use, in pg_hba.conf add the following under the line that looks like # TYPE DATABASE USER ADDRESS METHOD.

  • Type
    • local (Unix domain socket) or host (TCP connection)
  • Database
    • Rails also needs to have access to the postgres database (to create new databases?)
    • postgres,gamocosm_development,gamocosm_test,gamocosm_production
  • User
    • gamocosm
  • Address
    • Leave blank for local type
    • Localhost is in ipv4 and ::1/128 in ipv6. My system used ipv6 (postgres did not match the entry when I entered localhost ipv4)
  • Method
    • trust
      • Easiest, but least secure. Typically ok on development machines. Blindly trusts the user
    • peer
      • Checks if the postgresql user matches the operating system user
      • Since config/database.yml specifies the database user to be "gamocosm", using this method is more troublesome, at least in development, because you have to either change that to your OS username and create a postgresql user with your username, or create a new OS account called "gamocosm" and a postgresql user "gamocosm"
    • ident
      • Same as peer but for network connections
    • md5
      • Client supplies an MD5-encrypted password
      • This is the recommended method

Example: local postgres,gamocosm_development,gamocosm_test,gamocosm_production gamocosm md5.
You will have to restart postgresql ((sudo) systemctl restart postgresql) for the changes to take effect.

Directory hierarchy

  • app: main source code
  • bin: rails stuff, don't touch
  • config: rails app configuration
  • db: rails app database stuff (schema, migrations, seeds)
  • lib: rails stuff, don't touch
  • log: 'nuff said
  • public: static files
  • sysadmin: stuff for the Gamocosm server (you can run your own server! This is a true open source project)
  • test-docker: use docker container to test most of app/workers/setup_server_worker.rb (more below)
  • test: pooteeweet
  • vendor: rails stuff, don't touch

Technical details



  • Gamocosm has a lot of infrastructure:
    • CloudFlare DNS API
    • Digital Ocean API
    • Digital Ocean servers/droplets
    • Minecraft and the server wrapper
    • Gamocosm Rails server
    • Gamocosm Sidekiq background workers
  • Avoid state and duplicating data (less chance of corruption, logic easier to debug than data)
  • Idempotency is good

Error handling

  • Methods that "do things" should return nil on success, or an object on error
  • Methods that "return things" should use String#error! to mark a return value is an error
    • This method takes 1 argument: a data object (can be nil)
    • e.g. 'API response code not 200'.error!(res)
    • String#error! returns an Error object; Error#to_s is overridden so the error message can be shown to the user, or the error data (Error#data) can be further inspected for handling
  • You can use .error? to check if a return value is an error. Error#error? is overriden to return true
  • This class and these methods are defined in config/initializers/monkey_patches.rb
  • Throw exceptions in "exceptional cases", when something is unexpected (e.g. bad user input is expected) or can't be handled without "blowing up"

Important checks

  • server.remote.exists?: !server.remote_id.nil?
  • server.remote.error?: whether there was an error or not retrieving info about a droplet from Digital Ocean
    • true if the user is missing his Digital Ocean API token, or if it's invalid
    • false if !server.remote.exists?
    • don't need to check this before server.remote actions (e.g. server.remote.create)
  • server.running?: server.remote.exists? && !server.remote.error? && server.remote.status == 'active'
  • user.digital_ocean.nil?: Digital Ocean API token missing
  • minecraft.node.error?: error communicating with Minecraft wrapper on server
  • minecraft.running?: server.running? && !node.error? && node.pid > 0 (notice symmetry with server.running?)

Background workers

  • Idempotent
  • Keep blocks inside timeouts as simple as possible, cleanup outside of timeout, try to stick to plain old datatypes
    • Use ActiveRecord::Base.connection_pool.with_connection do |conn| if threads (e.g. timeout) access the database
  • Run finite amount of times (keep track of how many times looped)
  • Reset the state of the server if anything goes wrong (any exit points)
  • Check that the remote exists and is not errored
  • Log errors to user minecraft server, include 'Aborting' when not finishing
  • 'Aborting' should always be followed by server.reset_state and return

Other useful stuff

  • Development/test user (from db/seed.rb): email "[email protected]", password "1234test", has the Digital Ocean api token from env.sh
    • the current tests don't use this, and mock all HTTP requests/responses
  • The Sidekiq web interface is mounted at /sidekiq
  • Sidekiq doesn't automatically reload source files when you edit them. You must restart it for changes to take effect
  • New Relic RPM is available in developer mode at /newrelic
  • Run the console: bundle exec rails c
  • Reset the database: bundle exec rake db:reset
  • Reset Sidekiq jobs: Sidekiq::Queue.new.each { |job| job.delete } in the rails console
  • Reset Sidekiq stats: Sidekiq::Stats.new.reset in the rails console
  • The deployment scripts and configuration are in the sysadmin/ directory
  • List of rake db commands: Stack Overflow


  • bundle exec rails test or ./tests.sh
  • tests use WebMock to mock http requests (no external requests)
  • RAILS_ENV=test bundle exec rails <s|c> to run the server or console (respectively) in test mode
  • Note: the test server, unlike the dev server, does not automatically reload source files when you change them

More testing by simulating a user server with Docker

Without a server to connect to, Gamocosm can't try SetupServerWorker or AutoshutdownMinecraftWorker.
"test-docker/" contains a Dockerfile for building a basic Fedora container with an SSH server (simulating a bare Digital Ocean server).
If you set $TEST_DOCKER to "true", the tests will assume there is a running Docker Gamocosm container to connect to.

tests.sh will build the image, start the container, and delete the container for you if you specify to use Docker.
Otherwise, it will run the tests normally (equivalent to bundle exec rails test).
You should have non-root access to Docker.
You could also manage Docker yourself; you can look at the tests.sh file for reference.

Example: TEST_DOCKER=true ./tests.sh


  • Special thanks to geetfun who helped with the original development
  • Special thanks to binary-koan (Jono Mingard) for designing the new theme! Looks awesome!
  • SuperMarioBro for helping iron out some initial bugs, adding support for more Minecraft flavours
  • bearbin for helping iron out some initial bugs
  • chiisana for feedback and other ideas, resources
  • KayoticSully for planning and development on the server wrapper API
  • Jadorel for feedback and helping iron out some bugs
  • Ajusa for helping with some bugs