Atomic Lifecycle for Writer Refresh + Hardswap

src/metrics/render/me_hardswap.rs

@@ -0,0 +1,156 @@
+use std::fmt::Write;
+
+use crate::transport::middle_proxy::MeApiHardswapSnapshot;
+
+pub(super) fn render(
+    out: &mut String,
+    snapshot: Option<&MeApiHardswapSnapshot>,
+    enabled: bool,
+) {
+    let snapshot = enabled.then_some(snapshot).flatten();
+    let pending = snapshot.is_some_and(|value| value.pending);
+    let pending_age_secs = snapshot
+        .and_then(|value| value.pending_age_secs)
+        .unwrap_or(0);
+    let pending_writers_current = snapshot
+        .map(|value| value.pending_writers_current)
+        .unwrap_or(0);
+    let pending_writer_deficit = snapshot
+        .map(|value| value.pending_writer_deficit)
+        .unwrap_or(0);
+    let pending_missing_dc_groups = snapshot
+        .map(|value| value.pending_missing_dc_groups)
+        .unwrap_or(0);
+    let pending_map_current = snapshot
+        .and_then(|value| value.pending_map_current)
+        .is_some_and(|value| value);
+    let orphan_warm_writers_current = snapshot
+        .map(|value| value.orphan_warm_writers_current)
+        .unwrap_or(0);
+    let replacement_preparing_current = snapshot
+        .map(|value| value.replacement_preparing_current)
+        .unwrap_or(0);
+    let replacement_retiring_current = snapshot
+        .map(|value| value.replacement_retiring_current)
+        .unwrap_or(0);
+
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_hardswap_pending Whether an ME hardswap generation is pending"
+    );
+    let _ = writeln!(out, "# TYPE telemt_me_hardswap_pending gauge");
+    let _ = writeln!(out, "telemt_me_hardswap_pending {}", usize::from(pending));
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_hardswap_pending_age_seconds Age of the pending ME hardswap generation"
+    );
+    let _ = writeln!(out, "# TYPE telemt_me_hardswap_pending_age_seconds gauge");
+    let _ = writeln!(
+        out,
+        "telemt_me_hardswap_pending_age_seconds {pending_age_secs}"
+    );
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_hardswap_pending_writers_current Authoritative warm writers in the pending generation"
+    );
+    let _ = writeln!(
+        out,
+        "# TYPE telemt_me_hardswap_pending_writers_current gauge"
+    );
+    let _ = writeln!(
+        out,
+        "telemt_me_hardswap_pending_writers_current {pending_writers_current}"
+    );
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_hardswap_pending_writer_deficit Writers missing from the pending generation floor"
+    );
+    let _ = writeln!(
+        out,
+        "# TYPE telemt_me_hardswap_pending_writer_deficit gauge"
+    );
+    let _ = writeln!(
+        out,
+        "telemt_me_hardswap_pending_writer_deficit {pending_writer_deficit}"
+    );
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_hardswap_pending_missing_dc_groups Desired DC groups missing pending-generation coverage"
+    );
+    let _ = writeln!(
+        out,
+        "# TYPE telemt_me_hardswap_pending_missing_dc_groups gauge"
+    );
+    let _ = writeln!(
+        out,
+        "telemt_me_hardswap_pending_missing_dc_groups {pending_missing_dc_groups}"
+    );
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_hardswap_pending_map_current Whether the pending generation targets the current endpoint map"
+    );
+    let _ = writeln!(out, "# TYPE telemt_me_hardswap_pending_map_current gauge");
+    let _ = writeln!(
+        out,
+        "telemt_me_hardswap_pending_map_current {}",
+        usize::from(pending_map_current)
+    );
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_hardswap_orphan_warm_writers_current Warm writers not owned by the pending hardswap generation"
+    );
+    let _ = writeln!(
+        out,
+        "# TYPE telemt_me_hardswap_orphan_warm_writers_current gauge"
+    );
+    let _ = writeln!(
+        out,
+        "telemt_me_hardswap_orphan_warm_writers_current {orphan_warm_writers_current}"
+    );
+    let _ = writeln!(
+        out,
+        "# HELP telemt_me_writer_replacement_current ME writer replacements by transaction phase"
+    );
+    let _ = writeln!(out, "# TYPE telemt_me_writer_replacement_current gauge");
+    let _ = writeln!(
+        out,
+        "telemt_me_writer_replacement_current{{state=\"preparing\"}} {replacement_preparing_current}"
+    );
+    let _ = writeln!(
+        out,
+        "telemt_me_writer_replacement_current{{state=\"retiring\"}} {replacement_retiring_current}"
+    );
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn renders_bounded_hardswap_and_replacement_state() {
+        let snapshot = MeApiHardswapSnapshot {
+            pending: true,
+            pending_age_secs: Some(42),
+            pending_writers_current: 3,
+            pending_writer_deficit: 4,
+            pending_missing_dc_groups: 2,
+            pending_map_current: Some(true),
+            orphan_warm_writers_current: 1,
+            replacement_preparing_current: 5,
+            replacement_retiring_current: 6,
+        };
+        let mut out = String::new();
+
+        render(&mut out, Some(&snapshot), true);
+
+        assert!(out.contains("telemt_me_hardswap_pending 1"));
+        assert!(out.contains("telemt_me_hardswap_pending_age_seconds 42"));
+        assert!(out.contains("telemt_me_hardswap_pending_writer_deficit 4"));
+        assert!(out.contains(
+            "telemt_me_writer_replacement_current{state=\"preparing\"} 5"
+        ));
+        assert!(out.contains(
+            "telemt_me_writer_replacement_current{state=\"retiring\"} 6"
+        ));
+    }
+}