feat(telemetry): register metrics via callback (#1062)

## Summary
Register metrics for a service through a callback on the telemetry
builder.

## Background
`astria_telemetry::Config` should be the central entry point to
configure telemetry and metrics. Before this patch the metrics provider,
buckets, and global labels were set through config, but actual metrics
specific outside of it. With this patch this is done in one step.

## Changes
- add `Config::register_metrics` on telemetry builder
- change all services to pass their initialization function to it. 

## Testing
Must be observed in a dev cluster.

crates/astria-composer/src/main.rs

@@ -38,11 +38,10 @@ async fn main() -> ExitCode {
     if !cfg.no_metrics {
         telemetry_conf = telemetry_conf
             .metrics_addr(&cfg.metrics_http_listener_addr)
-            .service_name(env!("CARGO_PKG_NAME"));
+            .service_name(env!("CARGO_PKG_NAME"))
+            .register_metrics(metrics_init::register);
     }
 
-    metrics_init::register();
-
     if let Err(e) = telemetry_conf
         .try_init()
         .wrap_err("failed to setup telemetry")

crates/astria-conductor/src/main.rs

@@ -45,7 +45,8 @@ async fn main() -> ExitCode {
     if !cfg.no_metrics {
         telemetry_conf = telemetry_conf
             .metrics_addr(&cfg.metrics_http_listener_addr)
-            .service_name(env!("CARGO_PKG_NAME"));
+            .service_name(env!("CARGO_PKG_NAME"))
+            .register_metrics(|| {}); // conductor currently has no metrics
     }
 
     if let Err(e) = telemetry_conf

crates/astria-sequencer-relayer/src/main.rs

@@ -35,9 +35,9 @@ async fn main() -> ExitCode {
     if !cfg.no_metrics {
         telemetry_conf = telemetry_conf
             .metrics_addr(&cfg.metrics_http_listener_addr)
-            .service_name(env!("CARGO_PKG_NAME"));
+            .service_name(env!("CARGO_PKG_NAME"))
+            .register_metrics(metrics_init::register);
     }
-    metrics_init::register();
 
     if let Err(e) = telemetry_conf
         .try_init()

crates/astria-sequencer/src/main.rs

@@ -36,9 +36,9 @@ async fn main() -> ExitCode {
     if !cfg.no_metrics {
         telemetry_conf = telemetry_conf
             .metrics_addr(&cfg.metrics_http_listener_addr)
-            .service_name(env!("CARGO_PKG_NAME"));
+            .service_name(env!("CARGO_PKG_NAME"))
+            .register_metrics(metrics_init::register);
     }
-    metrics_init::register();
 
     if let Err(e) = telemetry_conf
         .try_init()

crates/astria-telemetry/src/lib.rs

@@ -74,6 +74,10 @@ impl Error {
     fn exporter_install(source: BuildError) -> Self {
         Self(ErrorKind::ExporterInstall(source))
     }
+
+    fn no_metric_register_func() -> Self {
+        Self(ErrorKind::NoMetricRegisterFunc)
+    }
 }
 
 #[derive(Debug, thiserror::Error)]
@@ -90,6 +94,11 @@ enum ErrorKind {
     BucketError(#[source] BuildError),
     #[error("failed installing prometheus metrics exporter")]
     ExporterInstall(#[source] BuildError),
+    #[error(
+        "telemetry was configured to run with metrics, but no function/closure to register \
+         metrics was provided"
+    )]
+    NoMetricRegisterFunc,
 }
 
 #[must_use = "the otel config must be initialized to be useful"]
@@ -136,6 +145,7 @@ pub struct Config {
     metrics_addr: Option<String>,
     service_name: String,
     metric_buckets: Option<Vec<f64>>,
+    register_metrics: Option<Box<dyn Fn()>>,
 }
 
 impl Config {
@@ -150,6 +160,7 @@ impl Config {
             metrics_addr: None,
             service_name: String::new(),
             metric_buckets: None,
+            register_metrics: None,
         }
     }
 }
@@ -237,6 +248,14 @@ impl Config {
         }
     }
 
+    #[must_use = "telemetry must be initialized to be useful"]
+    pub fn register_metrics<F: Fn() + 'static>(self, f: F) -> Self {
+        Self {
+            register_metrics: Some(Box::new(f)),
+            ..self
+        }
+    }
+
     /// Initialize telemetry, consuming the config.
     ///
     /// # Errors
@@ -252,6 +271,7 @@ impl Config {
             metrics_addr,
             service_name,
             metric_buckets,
+            register_metrics,
         } = self;
 
         let env_filter = {
@@ -322,6 +342,11 @@ impl Config {
                     .map_err(Error::bucket_error)?;
             }
 
+            let Some(register_metrics) = register_metrics else {
+                return Err(Error::no_metric_register_func());
+            };
+            register_metrics();
+
             metrics_builder.install().map_err(Error::exporter_install)?;
         }