SLS is a declarative orchestration system for ephemeral game servers, designed especially for server networks. Everything in SLS is reproducible, isolated, and fully defined through Blueprints.

SLS runs every game server inside its own Docker container, keeping environments clean, consistent and secure.

SLS is free and open-source software licensed under AGPL-3.0.

Protocube

Protocube is the core controller for SLS, responsible for managing all server instances across the system. It provides a REST API for creating, managing, and monitoring servers.

Docs:

• API Docs (Coming Soon)
• Plugin Docs (Coming Soon)
• Setup (Coming Soon)

Daemon

The server control plane for SLS. Each Daemon is responsible for provisioning, controlling and monitoring servers inside isolated Docker containers, exactly as defined by their Blueprints.

S4J

A Java wrapper for the Protocube API, providing a clean interface for plugins and external tools.

Blueprints

Blueprints are declarative specifications describing exactly how a game server should run: its software, world, version, limits, configuration patches, and bundled content.

Below is a full example Blueprint.

# Blueprint metadata
blueprint:
  id: "blueprint"                # Unique slug ID
  name: "Blueprint Name"         # Human-readable name
  type: "game"                   # Arbitrary grouping tag

# Traits are reusable configuration layers applied to this blueprint.
# Traits are merged in order from top to bottom.
# If multiple traits define the same field, the last trait listed wins.
# Values defined directly in this blueprint always override trait values.
traits:
  - LightWeight
  - CFGPatch
  - PluginAnnotations

# Server runtime configuration
# If the software includes an installation script the servers base files
# will be installed once per version at /servers/<software>/<version>
# (or a custom path if specified).
server:
  software: "platform"
  version: "1.0.0"
  image: "sls:java_21"

  # optional override
  # path: "custom/path"

  # Resource limits applied to the container
  limits:
    # The total amount of memory in mebibytes that this server is allowed to
    # use on the host system.
    memory_limit: 4096
    # The amount of additional swap space to be provided to a container instance.
    swap: 1024
    # The relative weight for IO operations in a container. This is relative to other
    # containers on the system and should be a value between 10 and 1000.
    io_weight: 500
    # The percentage of CPU that this instance is allowed to consume relative to
    # the host. A value of 200% represents complete utilization of two cores. This
    # should be a value between 1 and THREAD_COUNT * 100.
    cpu_limit: 200
    # The amount of disk space in megabytes that a server is allowed to use.
    disk_space: 5120
    # Sets which CPU threads can be used by the docker instance.
    threads: ""
    # Terminates the server if it breaches the memory limits.
    # Enabling OOM killer may cause server processes to exit unexpectedly.
    oom_disabled: false

  # Configuration patches applied at startup
  configs:
    server.properties:
      parser: properties
      find:
        motd: "Blueprint Server"

# Declarative server state
state:

  # Volumes are managed storage units.
  # All volume sources are resolved relative to the sls
  # configured volumes directory (e.g. /sls/volumes).
  #
  # Volumes cannot escape this directory and are never arbitrary host paths.
  volumes:
    # Server world state
    - name: "world"
      source: "worlds/world"     # Resolved to /sls/volumes/worlds/world
      target: "/world"           # Mount point inside the container
      mode: cow                  # cow | ro | rw (default: cow)

    # Read-only plugins or assets
    - name: "plugins"
      source: "plugins"
      target: "/plugins"
      mode: ro

    # Example persistent data volume
    # (useful for databases, player data, etc.)
    - name: "data"
      source: "shared/data"
      target: "/data"
      mode: rw

  # Explicit host mounts
  # These mount arbitrary host paths directly into the container.
  # They must be explicitly allowed in the daemon configuration.
  # ro = read-only, rw = read-write (default)
  mounts:
    - /host/path:/home/container:ro

  # Copy files into server filesystem at creation
  # - Files inside the SLS folder can always be copied
  # - Files outside the SLS folder require the source path to be listed in the daemon's allowed_mounts
  # Destinations are always relative to the server filesystem
  copy:
    - sls/files/config.yml:plugins/config.yml

  # Lifecycle hooks executed at specific events
  hooks:
    start:
      - echo "Server starting"
    running:
      - echo "Server started successfully"
    stopping:
      - echo "Server stopping server"

  # Environment variables for the server
  env:
    VAR: "var"
    ENABLE_FEATURE_X: "true"

# Whether servers created from this blueprint persist after shutdown.
# If false, the server instance and all non-persistent volume state
# are destroyed when the server stops.
save: false

# Arbitrary metadata for external systems
annotations:
  maintainer: "Maintainer"
  tags: ["game", "example"]

Development Status

Warning

This version of SLS is in active development and is not yet ready for use.

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