Return redirect if remove on follower

Fixes issue #391.

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## 4.2.3 (unreleased)
 - [PR #389](https://github.com/rqlite/rqlite/pull/389): Log Store directory path on startup.
+- [PR #392](https://github.com/rqlite/rqlite/pull/392): Return redirect if node removal attempted on follower. Fixes [issue #391](https://github.com/rqlite/rqlite/issues/391).
 
 ## 4.2.2 (December 7th 2017)
 - [PR #383](https://github.com/rqlite/rqlite/pull/383): Fix unit tests after underlying SQLite master table changes.

http/service.go

@@ -355,6 +355,18 @@ func (s *Service) handleRemove(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if err := s.store.Remove(remoteAddr); err != nil {
+		if err == store.ErrNotLeader {
+			leader := s.store.Peer(s.store.Leader())
+			if leader == "" {
+				http.Error(w, err.Error(), http.StatusServiceUnavailable)
+				return
+			}
+
+			redirect := s.FormRedirect(r, leader)
+			http.Redirect(w, r, redirect, http.StatusMovedPermanently)
+			return
+		}
+
 		w.WriteHeader(http.StatusInternalServerError)
 		return
 	}

store/store.go

@@ -597,9 +597,15 @@ func (s *Store) Join(addr string) error {
 // Remove removes a node from the store, specified by addr.
 func (s *Store) Remove(addr string) error {
 	s.logger.Printf("received request to remove node %s", addr)
+	if s.raft.State() != raft.Leader {
+		return ErrNotLeader
+	}
 
 	f := s.raft.RemovePeer(addr)
 	if f.Error() != nil {
+		if f.Error() == raft.ErrNotLeader {
+			return ErrNotLeader
+		}
 		return f.Error()
 	}
 	s.logger.Printf("node %s removed successfully", addr)