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Sidecar

The sidecar pattern is widely used in Kubernetes. It typically involves running a secondary container alongside the main application container to provide additional functionality. You can read more about the pattern here.

In this project, the sidecar acts as a communication bridge between the controller and the game server.

The sidecar exposes a simple REST API with a few routes that the server and controller interact with.

Routes

The sidecar provides the following endpoints:

  • GET /allow_delete
  • POST /allow_delete
  • GET /shutdown
  • POST /shutdown
  • /health

Allow Delete

The allow_delete routes are used to check or set whether the server is allowed to be deleted.

  • GET /allow_delete — Retrieve whether deletion is allowed.
  • POST /allow_delete — Set whether deletion is allowed.

Both the GET and POST methods operate on the same internal boolean value.

Request Format

JSON Example: 

{
  "allowed": true
}
Go Struct Example: 
type DeleteRequest struct {
    Allowed bool `json:"allowed"`
}

The boolean value controls whether the server considers itself safe to delete. * The controller usually issues GET requests to check the status. * The game server typically issues POST requests to update the status.

Note:

Be cautious when toggling the allowed state back to false. If the controller detects allowed = true, it may already begin the deletion process, even if you immediately set it back to false.

Shutdown

The shutdown routes indicate whether a shutdown has been requested for the server.

  • GET /shutdown — Retrieve whether shutdown has been requested.
  • POST /shutdown — Set whether shutdown has been requested.

Similar to allow_delete, these routes operate on an internal boolean value.

Request Format

JSON Example: 

{
  "shutdown": true,
}
Go Struct Example: 
type ShutdownRequest struct {
    Shutdown bool `json:"shutdown"`
}
The controller sets this flag once it detects a deletion timestamp on the Server object. The game server can poll this value to detect when a shutdown has been requested and gracefully handle it.

The communication workflow can be viewed here: Communication