aurora: Detect blue/green deployment switchovers via DNS mismatch

include/AuroraMonitorDecision.h

@@ -0,0 +1,34 @@
+/**
+ * @file AuroraMonitorDecision.h
+ * @brief Pure decision functions for Aurora monitor blue/green detection.
+ *
+ * Extracted from MySQL_Monitor_Connection_Pool for unit testability.
+ * These functions have no global state dependencies.
+ */
+
+#ifndef __CLASS_AURORA_MONITOR_DECISION_H
+#define __CLASS_AURORA_MONITOR_DECISION_H
+
+/**
+ * @brief Determine if a returned connection should be rejected based on
+ *        switchover timing.
+ *
+ * A connection is considered stale (pre-switchover) if it was checked out
+ * before the switchover was detected for its hostname.
+ *
+ * @param checkout_time    Monotonic timestamp when the connection was checked out or created.
+ *                         0 means unknown (non-Aurora monitor thread); always accepted.
+ * @param switchover_time  Timestamp when the switchover was detected for the hostname.
+ *                         0 means no switchover recorded.
+ * @return true if the connection should be rejected (stale), false if it can be re-pooled.
+ */
+inline bool should_reject_pooled_connection(
+	unsigned long long checkout_time,
+	unsigned long long switchover_time
+) {
+	if (switchover_time == 0) return false;
+	if (checkout_time == 0) return false;
+	return checkout_time < switchover_time;
+}
+
+#endif // __CLASS_AURORA_MONITOR_DECISION_H

include/DNS_Cache.hpp

@@ -83,6 +83,16 @@ class DNS_Cache {
 	void clear();
 	bool empty() const;
 	std::string lookup(const std::string& hostname, size_t* ip_count) const;
+	/**
+	 * @brief Check if a hostname's cached IPs include the given IP.
+	 * @param hostname The hostname to look up in the cache.
+	 * @param ip The IP address to search for.
+	 * @return true if the IP is found, or if the cache is disabled, or if
+	 *         the hostname is not in the cache (no evidence of mismatch).
+	 *         Returns false only when the hostname IS cached and the IP is
+	 *         NOT among its resolved addresses.
+	 */
+	bool contains_ip(const std::string& hostname, const std::string& ip) const;
 
 private:
 	struct IP_ADDR {

include/MySQL_Monitor.hpp

@@ -264,6 +264,12 @@ class MySQL_Monitor_State_Data {
 	 * @details Currently only used by 'group_replication'.
 	 */
 	uint64_t init_time = 0;
+	/**
+	 * @brief Monotonic time when a pooled connection was checked out via get_connection().
+	 * @details Used by blue/green switchover detection to reject pre-switchover connections.
+	 *          Set once at checkout, never modified. 0 if connection was newly created.
+	 */
+	unsigned long long pool_checkout_time = 0;
 	/**
 	 * @brief Used by GroupReplication to determine if servers reported by cluster 'members' are already monitored.
 	 * @details This way we avoid non-needed locking on 'MySQL_HostGroups_Manager' for server search.

lib/DNS_Cache.cpp

@@ -347,3 +347,33 @@ bool DNS_Cache::empty() const {
 
 	return result;
 }
+
+/**
+ * @brief Check if a hostname's cached IPs include the given IP.
+ * @param hostname The hostname to look up in the cache.
+ * @param ip The IP address to search for.
+ * @return true if found, cache disabled, or hostname not cached. false only
+ *         when hostname IS cached and ip is NOT among its resolved addresses.
+ */
+bool DNS_Cache::contains_ip(const std::string& hostname, const std::string& ip) const {
+	if (!enabled) return true;
+
+	int rc = pthread_rwlock_rdlock(&rwlock_);
+	assert(rc == 0);
+
+	bool found = true;
+	auto itr = records.find(hostname);
+	if (itr != records.end()) {
+		found = false;
+		for (const auto& cached_ip : itr->second.ips) {
+			if (cached_ip == ip) {
+				found = true;
+				break;
+			}
+		}
+	}
+
+	rc = pthread_rwlock_unlock(&rwlock_);
+	assert(rc == 0);
+	return found;
+}