Checks

Marathon already has the concept of health checks and readiness checks, which either monitor the health of an application or provide an indication that the service is ready. Both of these features in Marathon will indicate that the app/pod is “in deployment”.

Checks provide an abstract way to check on a task in Mesos providing values back via tasks and podstatus which are not interpreted by Marathon. They are intended to be consumed by services external to Marathon which will take appropriate action on them. You can think of them as a health check without a kill policy. The most significant aspect of them is that Marathon does not evaluate anything about the return values of a check.

Checks can be defined as:

HTTP Check
TCP Check
Command Check

When a check is configured for an app/pod, it has zero impact on its deployment status in Marathon. To control this behavior you will need to use a health check or readiness check. The value in the task varies depending on check type:

HTTP Check returns http response status code "checkResult":{"http":{"statusCode":200}}
TCP Check returns boolean true or false "checkResult":{"tcp":{"succeeded":true}}
Command Check returns the command process exit code checkResult":{"command":{"exitCode":0}}

Check options

http (Optional. ): HTTP Check object (see below). You can only have one check type (http, tcp, or exec).
tcp (Optional. ): TCP Check object (see below). You can only have one check type (http, tcp, or exec).
exec (Optional. ): Command Check object (see below). You can only have one check type (http, tcp, or exec).
intervalSeconds (Optional. Default: 60 seconds): Number of seconds to wait between checks.
timeoutSeconds (Optional. Default: 20 seconds): Number of seconds after which a check times out, regardless of the response. This value must be smaller than intervalSeconds.
delaySeconds (Optional. Default: 15): Amount of time to wait until starting the checks.

HTTP Check options

portIndex (Optional. ): The index of the port defined. The value 0 will be $PORT0 in the application. You can use either port OR portIndex, but not both.
port (Optional. ): Specific port to check. This is useful when using a network overlay or have a fixed port. You can use either port OR portIndex, but not both.
path (Optional. Default: "/"): Path to the endpoint the task exposes to provide check status. Example: /path/to/check.
scheme (Optional. Default: "HTTP"): Protocol of the requests to be performed. Only HTTP is currently supported.

TCP Check options

portIndex (Optional. ): The index of the port defined. The value 0 will be $PORT0 in the application. You can either use port OR portIndex, but not both.
port (Optional. ): Specific port to check. This is useful when using a network overlay or have a fixed port. You can either use port OR portIndex, but not both.

Command Check options

shell (Optional. ): Object of the command to execute.

Example HTTP Check Usage

"check":
{
  "id": "http-index-test",
  "cmd": "python3 -m http.server $PORT0",
  "cpus": 1,
  "mem": 128,
  "disk": 0,
  "instances": 1,
  "portDefinitions": [
    {
      "port": 0,
      "protocol": "tcp",
      "name": "http"
    }],
  "requirePorts" : false,
  "env": {},
  "labels": {},
  "check": {
    "http" : {
      "portIndex": 0,
      "path": "/"
    },
    "intervalSeconds": 60,
    "timeoutSeconds": 20
  }
}

Example Command Check Usage

"check":
{
  "id": "sarah-command-check",
  "cmd": "sleep inf",
  "cpus": 1,
  "mem": 128,
  "disk": 0,
  "instances": 1,
  "check": {
    "exec": {
      "command": {
        "shell": "ls"
      }
    },
    "intervalSeconds": 60,
    "timeoutSeconds": 20
  }
}