Struct Exposition 

pub struct Exposition { /* private fields */ }

Available on crate feature telemetry only.

One or more configurations’ ConfigStatus, as Prometheus text.

Built per scrape and thrown away: every sample comes from status, which is atomic loads and no I/O, so there is no state here worth keeping between scrapes and nothing to go stale.

What it emits

Name	Type	Extra label	Value
dynamic_config_installs_total	counter		installs since the process started
dynamic_config_last_success_seconds	gauge		seconds since the serving snapshot landed
dynamic_config_consecutive_failures	gauge		failures since the last install; zero is healthy
dynamic_config_last_failure_seconds	gauge		seconds since the last failure
dynamic_config_last_reload_info	gauge	reason	1
dynamic_config_last_failure_info	gauge	kind	1

The two _seconds families and the two failure families are absent rather than zero where the fact does not exist yet: a configuration that has never been installed has no staleness, and zero would read as “installed just now”, which is the opposite. last_success_seconds is the one an alert is written against — this service’s configuration has been stale for an hour is the page that matters, and nothing else here implies it.

A RemoteStatus added through add_remote renders as six more families, and the labels are the caller’s in exactly the same way:

Name	Type	Extra label	Value
dynamic_config_remote_up	gauge		1 if the store answered last time, 0 if not
dynamic_config_remote_fetches_total	counter		documents the store has handed over
dynamic_config_remote_last_fetch_seconds	gauge		seconds since it last handed one over
dynamic_config_remote_last_fetch_duration_seconds	gauge		how long the last pull took
dynamic_config_remote_consecutive_failures	gauge		fetches that returned nothing since one did
dynamic_config_remote_last_failure_info	gauge	kind	1

remote_up is absent before the first fetch, on the same principle as the two _seconds families: a source that has been installed and never asked is not down, and a 0 that means “not yet” is a page nobody should be woken by.

Cardinality

Bounded by the caller, and stated so it can be checked. For C configurations and R remote sources added — R ≤ C, because a configuration type has one Remote:

	per scrape	over a process’s life
a ConfigStatus	6 × C	(4 + 5 + 10) × C = 19 × C
a RemoteStatus	6 × R	(5 + 10) × R = 15 × R

so at most 6 × C + 6 × R ≤ 12 × C series in a scrape and 34 × C distinct series in total. The label sets come from fixed enums — five reload reasons and ten error kinds — and C is the number of configurations a process has, which is a handful.

A per-store series multiplies by a bounded number, which is why it exists; a per-key one would not, which is why there is no method here that could make one.

No key path, file name, store key or configured value is ever a label, and there is no method here that could make one: labels are the caller’s own, and everything derived from a status is a count, a duration or a fixed enum’s name.

Example

use dynamic_config::{telemetry::Exposition, ConfigCell};

static PORT: ConfigCell<u16> = ConfigCell::new();
PORT.store(8080);

let mut exposition = Exposition::new();
exposition.add("listener", &PORT.status());

let rendered = exposition.render();
assert!(rendered.contains(r#"dynamic_config_installs_total{config="listener"} 1"#));

Implementations

impl Exposition

pub fn new() -> Self

An empty exposition.

pub fn add(&mut self, config: &str, status: &ConfigStatus)

Adds one configuration, labelled config="…".

The name is the caller’s: a section key, a service name, whatever distinguishes this configuration from the others in the process. Not a path or anything derived from the document.

pub fn add_with(&mut self, labels: &[(&str, &str)], status: &ConfigStatus)

add, with labels of the caller’s choosing.

For a process whose configurations need two dimensions rather than one — a config server’s application and profile, say. Label names are sanitised to Prometheus’s [a-zA-Z_][a-zA-Z0-9_]* and values are escaped, so no caller can break out of the exposition; the cardinality of what is passed stays the caller’s own decision, and the type’s documentation says what a safe one looks like.

pub fn add_remote(&mut self, config: &str, status: &RemoteStatus)

Adds one remote source, labelled config="…".

The same name the configuration’s own add was given, so the two halves join in a query: dynamic_config_remote_up and dynamic_config_last_success_seconds for one config are the store answered and the document installed, which is the pair an operator is comparing.

Not the store’s URL, and there is no overload that takes one: a store URL routinely embeds user:password@host, so the name a series carries is the caller’s own — the same rule, and the same reason, as for a key path.

pub fn add_remote_with( &mut self, labels: &[(&str, &str)], status: &RemoteStatus, )

add_remote, with labels of the caller’s choosing — as add_with is to add.

pub fn render(&self) -> String

The exposition, as a Prometheus text body.

The durations are measured here rather than at add, so they are as fresh as the response is.

Trait Implementations

impl Clone for Exposition

fn clone(&self) -> Exposition

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Exposition

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Exposition

fn default() -> Exposition

Returns the “default value” for a type.

impl Display for Exposition

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.