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 --recursive `iquery --find` .
a/root.inspect:
  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/root.inspect:
  fuchsia.inspect.Health:
    start_timestamp_nanos = ...
    status = OK
c/root.inspect:
  fuchsia.inspect.Health:
    start_timestamp_nanos = ...
    status = UNHEALTHY
    message = "Failed to connect to fuchsia.example.RequiredService"

$ iquery --health a/root.inspect b/root.inspect c/root.inspect
a/root.inspect = OK
b/root.inspect = OK
c/root.inspect = UNHEALTHY (Failed to connect to fuchsia.example.RequiredService)

$ iquery --health --summary a/root.inspect b/root.inspect c/root.inspect
c/root.inspect = UNHEALTHY (Failed to connect to fuchsia.example.RequiredService)

$ iquery --health --summary a/root.inspect b/root.inspect not_found/root.inspect
not_found/root.inspect = NOT_FOUND

$ iquery --health --recursive a/root.inspect b/root.inspect c/root.inspect
a/root.inspect = HEALTHY
a/root.inspect#connections/0 = STARTING_UP
a/root.inspect#optional_database = UNHEALTHY (Cannot open local.file)
b/root.inspect = OK
c/root.inspect = UNHEALTHY (Failed to connect to fuchsia.example.RequiredService)

Using health checks in components

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

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.
}