PIP-121: Implement AutoClusterFailover (#547)

Author: BewareMyPower

include/pulsar/AutoClusterFailover.h

@@ -0,0 +1,116 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+#ifndef PULSAR_AUTO_CLUSTER_FAILOVER_H_
+#define PULSAR_AUTO_CLUSTER_FAILOVER_H_
+
+#include <pulsar/ServiceInfoProvider.h>
+
+#include <chrono>
+#include <cstdint>
+#include <functional>
+#include <memory>
+#include <vector>
+
+namespace pulsar {
+
+class Client;
+class AutoClusterFailoverImpl;
+
+class PULSAR_PUBLIC AutoClusterFailover final : public ServiceInfoProvider {
+   public:
+    struct Config {
+        const ServiceInfo primary;
+        const std::vector<ServiceInfo> secondary;
+        std::chrono::milliseconds checkInterval{5000};  // 5 seconds
+        uint32_t failoverThreshold{1};
+        uint32_t switchBackThreshold{1};
+
+        Config(ServiceInfo primary, std::vector<ServiceInfo> secondary)
+            : primary(std::move(primary)), secondary(std::move(secondary)) {}
+    };
+
+    /**
+     * Builder helps create an AutoClusterFailover configuration.
+     *
+     * Example:
+     *   ServiceInfo primary{...};
+     *   std::vector<ServiceInfo> secondaries{...};
+     *   AutoClusterFailover provider = AutoClusterFailover::Builder(primary, secondaries)
+     *       .withCheckInterval(std::chrono::seconds(5))
+     *       .withFailoverThreshold(3)
+     *       .withSwitchBackThreshold(3)
+     *       .build();
+     *
+     * Notes:
+     * - primary: the preferred cluster to use when available.
+     * - secondary: ordered list of fallback clusters.
+     * - checkInterval: frequency of health probes.
+     * - failoverThreshold: the number of consecutive failed probes required before switching away from
+     *   the current cluster.
+     * - switchBackThreshold: the number of consecutive successful probes to the primary required before
+     *   switching back from a secondary while that secondary remains available. If the active secondary
+     *   becomes unavailable and the primary is available, the implementation may switch back to the
+     *   primary immediately, regardless of this threshold.
+     */
+    class Builder {
+       public:
+        Builder(ServiceInfo primary, std::vector<ServiceInfo> secondary)
+            : config_(std::move(primary), std::move(secondary)) {}
+
+        // Set how frequently probes run against the active cluster(s). Default: 5 seconds.
+        Builder& withCheckInterval(std::chrono::milliseconds interval) {
+            config_.checkInterval = interval;
+            return *this;
+        }
+
+        // Set the number of consecutive failed probes required before attempting failover. Default: 1.
+        Builder& withFailoverThreshold(uint32_t threshold) {
+            config_.failoverThreshold = threshold;
+            return *this;
+        }
+
+        // Set the number of consecutive successful primary probes required before switching back from a
+        // healthy secondary. If the active secondary becomes unavailable and the primary is available,
+        // the implementation may switch back immediately regardless of this threshold. Default: 1.
+        Builder& withSwitchBackThreshold(uint32_t threshold) {
+            config_.switchBackThreshold = threshold;
+            return *this;
+        }
+
+        AutoClusterFailover build() { return AutoClusterFailover(std::move(config_)); }
+
+       private:
+        Config config_;
+    };
+
+    explicit AutoClusterFailover(Config&& config);
+
+    ~AutoClusterFailover() final;
+
+    ServiceInfo initialServiceInfo() final;
+
+    void initialize(std::function<void(ServiceInfo)> onServiceInfoUpdate) final;
+
+   private:
+    std::shared_ptr<AutoClusterFailoverImpl> impl_;
+};
+
+}  // namespace pulsar
+
+#endif