Node and Cluster Health Checks

Using health checks with your DC/OS cluster

Node and cluster health checks provide information about your cluster, including available ports, Mesos agent status, and IP detect script validation. A health check is a shell command that reports the status of a DC/OS cluster or node via its exit code. You can write your own custom health checks or use the predefined checks.

Predefined Health Checks

DC/OS includes a set of predefined built-in health checks for DC/OS core components. These built-in checks verify the following:

  • All DC/OS components are healthy.
  • The XZ utility is available.
  • The IP detect script produces valid output.
  • The Mesos agent has registered with the masters.

Custom Health Checks

Custom checks are checks written by a user and specified when installing DC/OS in the config.yaml file. Custom checks should be written for non-core DC/OS components. Health checks for DC/OS core components are included out-of-the-box as predefined health checks. For example, you can write custom health checks to verify the following:

  • The DC/OS service is healthy
  • The local mounts on nodes are healthy

Creating Custom Health Checks

Custom health checks are user-defined commands that are added to the set of checks that are executed when determining whether a node or cluster is healthy. A custom health check must report its status as one of the exit codes shown in the following table.

Code Status Description
0 OK Check passed. No investigation needed.
1 WARNING Check passed, but investigation may be necessary.
2 CRITICAL Check failed. Investigate if unexpected.
3 or greater UNKNOWN Status cannot be determined. Investigate.

Optionally, you can configure the checks to output a human-readable message to stderr or stdout.

Specifying Custom Health Checks

Before installing DC/OS, you must specify custom health checks in the custom_checks installation configuration parameter. If you want to modify the configuration file after installation, you must follow the DC/OS upgrade process.

If it is an absolute path (for example, if you have an executable in /usr/bin/), you can specify it directly in the cmd. If you reference an executable by name without an absolute path (for example, echo instead of /usr/bin/echo), the system will look for it by using this search path, and use the first executable that it finds: /opt/mesosphere/bin:/usr/bin:/bin:/sbin.

For a description of this parameter and examples, see the configuration parameter documentation.

Custom Health Check Executables

Before installing DC/OS, you may optionally provide a directory of executables at genconf/check_bins/ that will be distributed to all cluster nodes for use in custom checks. If provided, these executables will be added to the end of the search path for check executables. In order to use custom check executables, reference them in the custom_checks parameter by name without an absolute path (for example, to use genconf/check_bins/custom_script.sh in a custom check, refer to it as custom_script.sh).

Types of Health Checks

Cluster Checks

Cluster checks report the health status of the entire DC/OS cluster. Cluster checks are available across your cluster on all nodes. You can discover which cluster checks have been defined by SSHing to your cluster node and running this command: /opt/mesosphere/bin/dcos-shell dcos-check-runner check cluster --list.

Node Checks

Node checks report the status of individual nodes after installation. Node checks can be run post-installation by connecting to an individual node via SSH. You can view which node checks have been defined by SSHing to your cluster node and running this command: /opt/mesosphere/bin/dcos-shell dcos-check-runner check node-poststart --list.

Running Health Checks

You can run the following commands from your cluster node to invoke custom or predefined health checks.

Prerequisites:

  • DC/OS is installed and you are logged in with superuser permission.

  1. SSH to a cluster node.

    dcos node --master-proxy --mesos-id=<agent-node-id>

  2. Run this command to view the available health checks, with your check type (<check-type>) specified. The check type can be either cluster (cluster) or node (node-poststart).

    /opt/mesosphere/bin/dcos-shell dcos-check-runner check <check-type> --list

    Your output should resemble:

    {
  "clock_sync": {
    "description": "System clock is in sync.",
    "cmd": [
      "/opt/mesosphere/bin/dcos-checks",
      "time"
    ],
    "timeout": "1s"
  },
  "components_agent": {
    "description": "All DC/OS components are healthy",
    "cmd": [
      "/opt/mesosphere/bin/dcos-checks",
      "--role",
      "agent",
      "--iam-config",
      "/run/dcos/etc/dcos-diagnostics/agent_service_account.json",
      "--force-tls",
      "--ca-cert=/run/dcos/pki/CA/ca-bundle.crt",
      "components",
      "--scheme",
      "https",
      "--port",
      "61002"
    ],
    "timeout": "3s"
  },
  ...

  3. Run checks with the check name (<checkname>) specified.

    /opt/mesosphere/bin/dcos-shell dcos-check-runner check node-poststart <checkname>

For example: To run the component_agent check.

```bash
/opt/mesosphere/bin/dcos-shell dcos-check-runner check node-poststart component_agent
```

The output should resemble:

```bash
{
  “status”: 2,
  “checks”: {
    “component_agent”: {
      “status”: 2,
      “output”: “”
    },
    “exhibitor”: {
      “status”: 0,
      “output”: “”
    }
  }
}
```

Examples

List all checks

List all cluster checks.

/opt/mesosphere/bin/dcos-shell dcos-check-runner check cluster --list

List all node checks.

/opt/mesosphere/bin/dcos-shell dcos-check-runner check node-poststart --list

List specific checks

List specific cluster checks (check1).

/opt/mesosphere/bin/dcos-shell dcos-check-runner check cluster --list check1 [check2 [...]]

List specific node checks (check1).

/opt/mesosphere/bin/dcos-shell dcos-check-runner check node-poststart --list check1 [check2 [...]]

Run all checks

Run cluster checks.

/opt/mesosphere/bin/dcos-shell dcos-check-runner check cluster

Run node checks.

/opt/mesosphere/bin/dcos-shell dcos-check-runner check node-poststart

Run specific checks

Run specific cluster checks (check1).

dcos-check-runner check cluster check1 [check2 [...]]

Run specific node checks (check1).

dcos-check-runner check node-poststart check1 [check2 [...]]