feat(cluster): implement distributed clustering with etcd coordination

- Integrate etcd-client for distributed coordination and leader election
- Add remote client macros with proper formatting for all services
- Implement RequestMetrics for tracking RPC performance and errors
- Add rate limiting mechanism across all service endpoints
- Create ElectionRequest and ElectionResult message types for leader election
- Add role management with primary/replica switching capabilities
- Implement health checker with automatic failover detection
- Add repository count metrics for cluster monitoring
- Update Cargo.toml with etcd-client and dashmap dependencies
- Modify RepoEntry to include read_only flag for replica handling
- Implement should_accept_election logic to prevent duplicate elections
- Add RoleChangedEvent handling for cluster role updates

server/archive.rs

@@ -3,7 +3,11 @@ use crate::pb::*;
 
 use super::{GitksService, cache, into_status};
 
-remote_client!(remote_archive_client, ArchiveServiceClient<tonic::transport::Channel>, "archive");
+remote_client!(
+    remote_archive_client,
+    ArchiveServiceClient<tonic::transport::Channel>,
+    "archive"
+);
 
 #[tonic::async_trait]
 impl archive_service_server::ArchiveService for GitksService {
@@ -14,7 +18,9 @@ impl archive_service_server::ArchiveService for GitksService {
         &self,
         request: tonic::Request<ArchiveRequest>,
     ) -> Result<tonic::Response<Self::GetArchiveStream>, tonic::Status> {
+        let m = crate::metrics::RequestMetrics::new("gitks.ArchiveService/GetArchive");
         let inner = request.into_inner();
+        let _rate = self.acquire_rate_limit(inner.repository.as_ref()).await?;
         let repo = self.repo_label(inner.repository.as_ref());
         let span = tracing::info_span!("archive.get_archive", %repo);
         let _enter = span.enter();
@@ -24,16 +30,22 @@ impl archive_service_server::ArchiveService for GitksService {
                 if let Some(mut client) =
                     remote_archive_client(self, inner.repository.as_ref(), false).await?
                 {
+                    m.record("ok");
                     let resp = client.get_archive(inner).await?;
                     let stream = super::bridge_server_stream(resp.into_inner());
                     return Ok(tonic::Response::new(stream));
                 }
+                crate::metrics::record_rpc_error(&m, &err);
+                return Err(err);
+            }
+            Err(err) => {
+                crate::metrics::record_rpc_error(&m, &err);
                 return Err(err);
             }
-            Err(err) => return Err(err),
         };
         let stream = gb.get_archive_stream(inner)?;
         tracing::info!(%repo, "archive streaming started");
+        m.record("ok");
         Ok(tonic::Response::new(stream))
     }
 
@@ -41,7 +53,9 @@ impl archive_service_server::ArchiveService for GitksService {
         &self,
         request: tonic::Request<ListArchiveEntriesRequest>,
     ) -> Result<tonic::Response<ListArchiveEntriesResponse>, tonic::Status> {
+        let m = crate::metrics::RequestMetrics::new("gitks.ArchiveService/ListArchiveEntries");
         let inner = request.into_inner();
+        let _rate = self.acquire_rate_limit(inner.repository.as_ref()).await?;
         let repo = self.repo_label(inner.repository.as_ref());
         let span = tracing::info_span!("archive.list_archive_entries", %repo);
         let _enter = span.enter();
@@ -51,11 +65,16 @@ impl archive_service_server::ArchiveService for GitksService {
                 if let Some(mut client) =
                     remote_archive_client(self, inner.repository.as_ref(), false).await?
                 {
+                    m.record("ok");
                     return client.list_archive_entries(inner).await;
                 }
+                crate::metrics::record_rpc_error(&m, &err);
+                return Err(err);
+            }
+            Err(err) => {
+                crate::metrics::record_rpc_error(&m, &err);
                 return Err(err);
             }
-            Err(err) => return Err(err),
         };
         let resp = if cache::selector_is_oid(&inner.treeish) {
             cache::cached_response("archive.list_archive_entries", &inner, || {
@@ -65,6 +84,7 @@ impl archive_service_server::ArchiveService for GitksService {
             gb.list_archive_entries(inner).map_err(into_status)?
         };
         tracing::info!(%repo, count = resp.entries.len(), "list_archive_entries done");
+        m.record("ok");
         Ok(tonic::Response::new(resp))
     }
 }