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Health Checks

Health Checks

Health checks may be specified per application to be run against that application's tasks.

  • The default health check defers to Mesos' knowledge of the task state TASK_RUNNING => healthy
  • Marathon provides a health member of the task resource via the [REST API]({{ site.baseurl }}/docs/rest-api.html).

A health check is considered passing if (1) its HTTP response code is between 200 and 399, inclusive, and (2) its response is received within the timeoutSeconds period. If a task fails more than maxConseutiveFailures health checks consecutively, that task is killed.

Example usage
{
  "path": "/api/health",
  "portIndex": 0,
  "protocol": "HTTP",
  "gracePeriodSeconds": 300,
  "intervalSeconds": 60,
  "timeoutSeconds": 20,
  "maxConsecutiveFailures": 3
}

OR

{
  "portIndex": 0,
  "protocol": "TCP",
  "gracePeriodSeconds": 300,
  "intervalSeconds": 60,
  "timeoutSeconds": 20,
  "maxConsecutiveFailures": 0
}

OR

{
  "protocol": "COMMAND",
  "command": { "value": "curl -f -X GET http://$HOST:$PORT0/health" },
  "gracePeriodSeconds": 300,
  "intervalSeconds": 60,
  "timeoutSeconds": 20,
  "maxConsecutiveFailures": 3
}

Health check options

  • gracePeriodSeconds (Optional. Default: 300): Health check failures are ignored within this number of seconds or until the task becomes healthy for the first time.
  • intervalSeconds (Optional. Default: 60): Number of seconds to wait between health checks.
  • maxConsecutiveFailures(Optional. Default: 3) : Number of consecutive health check failures after which the unhealthy task should be killed. If this value is 0, then tasks will not be killed due to failing this check.
  • path (Optional. Default: "/"): Path to endpoint exposed by the task that will provide health status. Example: "/path/to/health". Note: only used if protocol == "HTTP".
  • portIndex (Optional. Default: 0): Index in this app's ports array to be used for health requests. An index is used so the app can use random ports, like "[0, 0, 0]" for example, and tasks could be started with port environment variables like $PORT1.
  • protocol (Optional. Default: "HTTP"): Protocol of the requests to be performed. One of "HTTP" or "TCP".
  • timeoutSeconds (Optional. Default: 20): Number of seconds after which a health check is considered a failure regardless of the response.

Health Lifecycle

The application health lifecycle is represented by the finite state machine in figure 1 below. In the diagram:

  • i is the number of requested instances
  • r is the number of running instances
  • h is the number of healthy instances


Figure 1: The Application Health Lifecycle