Health check

Health check is a standardized inspection metric. Adding a fuchsia.inspect.Health child to an Inspect Node gives that node the contained health information. This information can be aggregated by system-wide health-checking tools.

The layout of the health check node

The following properties and metrics are exported in any health check node:

Name	Type	Description
`start_timestamp_nanos`	int64	The monotonic clock system timestamp at which this health node was initialized (i.e. first became `STARTING UP`)
`message`	String	If `status==UNHEALTHY`, this includes an optional failure detail message.
`status`	Enum	`STARTING_UP`: The health node was initialized but not yet marked running.
		`OK`: The subsystem reporting to this health node is reporting healthy.
		`UNHEALTHY`: The subsystem reporting to this health node is reporting unhealthy.

User guide

The following example illustrates the use of iquery for getting information about the component health status.

Examples:

$ iquery show `iquery list`
a.cmx:
  root:
    fuchsia.inspect.Health:
      start_timestamp_nanos = ...
      status = OK
    connections:
      0:
        fuchsia.inspect.Health:
          start_timestamp_nanos = ...
          status = STARTING_UP
    optional_database:
      fuchsia.inspect.Health:
        start_timestamp_nanos = ...
        status = UNHEALTHY
        message = "Cannot open local.file"
b.cmx:
  root:
    fuchsia.inspect.Health:
      start_timestamp_nanos = ...
      status = OK
c.cmx:
  root:
    fuchsia.inspect.Health:
      start_timestamp_nanos = ...
      status = UNHEALTHY
      message = "Failed to connect to fuchsia.example.RequiredService"

$ iquery show a.cmx:root/fuchsia.inspect.Health:status b.cmx:root/fuchsia.inspect.Healh:status c.cmx:root/fuchsia.inspect.Health:status
a:
  root:
    fuchsia.inspectHealth:
      status = Ok
b:
  root:
    fuchsia.inspectHealth:
      status = Ok
c:
  root:
    fuchsia.inspectHealth:
      status = Ok

Using health checks in components

The following sections explain how to use the library in Fuchsia components written in various programming languages.

C++

  #include <lib/async-loop/cpp/loop.h>
  #include <lib/async-loop/default.h>
  #include <lib/sys/cpp/component_context.h>
  #include <lib/sys/inspect/cpp/component.h>

  int main(int argc, char** argv) {
    async::Loop loop(&kAsyncLoopConfigAttachToCurrentThread);
    auto context = sys::ComponentContext::CreateAndServeOutgoingDirectory();
    sys::ComponentInspector inspector(context.get());
    inspector.Health().StartingUp();

    // ...Do startup work...

    inspector.Health().Ok();
    inspector.Health().Unhealthy("I'm not feeling well.");
    inspector.Health().Ok();

    loop.Run();
    return 0;
  }

Rust

  use fuchsia_inspect as inspect;
  use fuchsia_inspect::health;

  fn main() {
    // If you have your own inspector, it's also possible to export its health.

    /* inspector needs to be initialized */
    let inspector = /* ... */
    let mut node = inspector::root();
    let mut health = fuchsia_inspect::health::Node(node);
    // ...
    health.set_ok();
    health.set_unhealthy("I'm not feeling well.");
    health.set_ok();  // The component is healthy again.
  }

Dart

  import 'package:fuchsia_inspect/inspect.dart' as inspect;

  void main(List<String> args) {
    final inspector = inspect.Inspect();
    inspector.health.setStartingUp();
    // ...Do startup work...
    inspector.health.setOk();
    inspector.health.setUnhealthy("I'm not feeling well.");
    inspector.health.setOk();
  }