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Bumped snapshot timeout from 256 to 1024
Latest commit b083d5f Nov 16, 2019

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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.

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 20, but the steps should be similar on other distributions.

  1. Install postgresql and development headers and libraries, memcached, redis, and nodejs: (sudo) yum install postgresql-server postgresql-contrib postgresql-devel memcached redis nodejs
  2. Install RVM. Read the instructions on their page (will be up to date)
  3. Install Ruby 2.2.0+: rvm install 2.2, and optionally rvm use --default 2.2. You may need to install extra packages for compiling ruby (it will tell you)
  4. Install other things needed for gems: (sudo) yum install gcc
  5. Check that ruby -v gives you version 2.2. If not, log out and back in (on the computer) to have it reread your ~/.bash_profile
  6. Install Bundler: gem install bundler
  7. Install gem dependencies: bundle install
  8. Run cp
  9. Enter config in
  10. Initialize postgresql: (sudo) postgresql-setup initdb
  11. Start postgresql, memcached, and redis manually: (sudo) service start postgresql/memcached/redis, or enable them to start at boot time: (sudo) service enable postgresql/memcached/redis
  12. After configuring the database, run ./ rake db:setup
  13. Start the server: ./ rails s
  14. Start the Sidekiq worker: ./ sidekiq

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
  • server_setup: stuff for the servers Gamocosm creates (e.g. zram scripts), used by app/workers/setup_server_worker.rb
  • sysadmin: stuff for the Gamocosm server (you can run your own server! this is an 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 and options and both source for environment variables/configuration. also does bundle exec for you, so you just do ./ GEM ARGS ....

  • DIGITAL_OCEAN_API_KEY: your Digital Ocean api token
  • DIGITAL_OCEAN_SSH_PUBLIC_KEY_PATH: ssh key to be added to new servers to SSH into
  • SIDEKIQ_ADMIN_USERNAME: HTTP basic auth for Sidekiq web interface
  • DATABASE_USER: hmmmm
  • DATABASE_HOST: database host. If specified, Rails will use a TCP connection (e.g. "localhost"). If left blank, Rails will use a local Unix socket connection
  • MAIL_SERVER_*: see action mailer configuration in the Rails guide
  • USER_SERVERS_DOMAIN: subdomain for user servers (e.g.
  • CLOUDFLARE_ZONE: TODO explain how to get this
  • DEVISE_SECRET_KEY: only tests, production
  • SECRET_KEY: only production
  • DEVELOPER_EMAILS: comma separated list of emails to send exceptions to
  • BADNESS_SECRET: secret to protect /badness endpoint

Database configuration

Locate pg_hba.conf. On Fedora this is in /var/lib/pgsql/data/. This file tells postgresql how to authenticate users. Read about it on the PostgreSQL docs. To restart postgresql: (sudo) service postgresql restart config/database.yml gets the database username from the environment variable DATABASE_USER (default "gamocosm"). The default value in "" for DATABASE_HOST is blank, so if you don't change it Rails will use a local Unix socket connection. 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 - postgres
  • Run createuser --createdb --pwprompt --superuser gamocosm (createuser --help for more info)

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

  • Type
    • local (local Unix socket) or host (TCP connection)
  • Database
    • 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

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? && > 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 "", password "1234test", has the Digital Ocean api token from
    • 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: ./ rails c
  • Reset the database: ./ rake db:reset
  • Reset Sidekiq jobs: { |job| job.delete } in the rails console
  • Reset Sidekiq stats: in the rails console
  • The deployment scripts and configuration are in the sysadmin/ directory
  • List of rake db commands: Stack Overflow


  • ./ rake test or ./
  • tests use WebMock to mock http requests (no external requests)
  • RAILS_ENV=test ./ 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. 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 ./ rake test). You should have non-root access to Docker. You could also manage Docker yourself; you can look at the file for reference.

Example: TEST_DOCKER=true ./


  • 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
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