diff --git a/services/mam-api/src/db/migrations/007-cluster-dedupe-hostname.sql b/services/mam-api/src/db/migrations/007-cluster-dedupe-hostname.sql
new file mode 100644
index 0000000..4f13252
--- /dev/null
+++ b/services/mam-api/src/db/migrations/007-cluster-dedupe-hostname.sql
@@ -0,0 +1,20 @@
+-- 007 — De-duplicate cluster_nodes by hostname and enforce uniqueness.
+--
+-- Migration 004 created the table with `CREATE TABLE IF NOT EXISTS` and an
+-- inline UNIQUE constraint; on deploys where the table predated 004 the
+-- constraint was never applied, which let the same hostname accumulate
+-- multiple rows (one per container restart in some setups).
+--
+-- This migration:
+--   1. Deletes older duplicates keeping only the most-recently-seen row
+--      per hostname.
+--   2. Adds a UNIQUE INDEX on (hostname) which is idempotent and satisfies
+--      the ON CONFLICT (hostname) upsert in routes/cluster.js.
+
+DELETE FROM cluster_nodes a
+USING cluster_nodes b
+WHERE a.hostname = b.hostname
+  AND a.last_seen < b.last_seen;
+
+CREATE UNIQUE INDEX IF NOT EXISTS cluster_nodes_hostname_uniq
+  ON cluster_nodes (hostname);