health.md

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 ffx inspect for getting information about the component health status.

Examples:

$ ffx inspect show
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"

$ ffx inspect 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 = UNHEALTHY

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();
    }