feat: Block clio if migration is blocking (#1834)

Add:
- Block server if migration is blocking
- Initialise the migration related table when server starts against
empty DB

Add MigrationInspectorInterface. server uses inspector to check the
migrators status.

src/app/ClioApplication.cpp

@@ -26,6 +26,7 @@
 #include "etl/LoadBalancer.hpp"
 #include "etl/NetworkValidatedLedgers.hpp"
 #include "feed/SubscriptionManager.hpp"
+#include "migration/MigrationInspectorFactory.hpp"
 #include "rpc/Counters.hpp"
 #include "rpc/RPCEngine.hpp"
 #include "rpc/WorkQueue.hpp"
@@ -103,6 +104,16 @@ ClioApplication::run(bool const useNgWebServer)
     // Interface to the database
     auto backend = data::makeBackend(config_);
 
+    {
+        auto const migrationInspector = migration::makeMigrationInspector(config_, backend);
+        // Check if any migration is blocking Clio server starting.
+        if (migrationInspector->isBlockingClio() and backend->hardFetchLedgerRangeNoThrow()) {
+            LOG(util::LogService::error())
+                << "Existing Migration is blocking Clio, Please complete the database migration first.";
+            return EXIT_FAILURE;
+        }
+    }
+
     // Manages clients subscribed to streams
     auto subscriptions = feed::SubscriptionManager::makeSubscriptionManager(config_, backend);
 

src/migration/CMakeLists.txt

@@ -5,4 +5,4 @@ target_sources(
                          cassandra/impl/ObjectsAdapter.cpp cassandra/impl/TransactionsAdapter.cpp
 )
 
-target_link_libraries(clio_migration PRIVATE clio_util clio_etl)
+target_link_libraries(clio_migration PRIVATE clio_util clio_data)

src/migration/MigrationInspectorFactory.hpp

@@ -0,0 +1,65 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2025, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include "data/BackendInterface.hpp"
+#include "migration/MigrationInspectorInterface.hpp"
+#include "migration/MigratiorStatus.hpp"
+#include "migration/cassandra/CassandraMigrationManager.hpp"
+#include "util/Assert.hpp"
+#include "util/log/Logger.hpp"
+#include "util/newconfig/ConfigDefinition.hpp"
+
+#include <boost/algorithm/string.hpp>
+#include <boost/algorithm/string/predicate.hpp>
+
+#include <memory>
+#include <utility>
+
+namespace migration {
+
+/**
+ * @brief A factory function that creates migration inspector instance and initializes the migration table if needed.
+ *
+ * @param config The config.
+ * @param backend The backend instance. It should be initialized before calling this function.
+ * @return A shared_ptr<MigrationInspectorInterface> instance
+ */
+inline std::shared_ptr<MigrationInspectorInterface>
+makeMigrationInspector(
+    util::config::ClioConfigDefinition const& config,
+    std::shared_ptr<BackendInterface> const& backend
+)
+{
+    ASSERT(backend != nullptr, "Backend is not initialized");
+
+    auto inspector = std::make_shared<migration::cassandra::CassandraMigrationInspector>(backend);
+
+    // Database is empty, we need to initialize the migration table if it is a writeable backend
+    if (not config.get<bool>("read_only") and not backend->hardFetchLedgerRangeNoThrow()) {
+        migration::MigratorStatus migrated(migration::MigratorStatus::Migrated);
+        for (auto const& name : inspector->allMigratorsNames()) {
+            backend->writeMigratorStatus(name, migrated.toString());
+        }
+    }
+    return inspector;
+}
+
+}  // namespace migration

src/migration/MigrationInspectorInterface.hpp

@@ -0,0 +1,79 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2025, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include "migration/MigratiorStatus.hpp"
+
+#include <string>
+#include <tuple>
+#include <vector>
+
+namespace migration {
+
+/**
+ * @brief The interface for the migration inspector.The Clio server application will use this interface to inspect
+ * the migration status.
+ */
+struct MigrationInspectorInterface {
+    virtual ~MigrationInspectorInterface() = default;
+
+    /**
+     * @brief Get the status of all the migrators
+     * @return A vector of tuple, the first element is the migrator's name, the second element is the status of the
+     */
+    virtual std::vector<std::tuple<std::string, MigratorStatus>>
+    allMigratorsStatusPairs() const = 0;
+
+    /**
+     * @brief Get all registered migrators' names
+     *
+     * @return A vector of migrators' names
+     */
+    virtual std::vector<std::string>
+    allMigratorsNames() const = 0;
+
+    /**
+     * @brief Get the status of a migrator by its name
+     *
+     * @param name The migrator's name
+     * @return The status of the migrator
+     */
+    virtual MigratorStatus
+    getMigratorStatusByName(std::string const& name) const = 0;
+
+    /**
+     * @brief Get the description of a migrator by its name
+     *
+     * @param name The migrator's name
+     * @return The description of the migrator
+     */
+    virtual std::string
+    getMigratorDescriptionByName(std::string const& name) const = 0;
+
+    /**
+     * @brief Return if Clio server is blocked
+     *
+     * @return True if Clio server is blocked by migration, false otherwise
+     */
+    virtual bool
+    isBlockingClio() const = 0;
+};
+
+}  // namespace migration

src/migration/MigrationManagerInterface.hpp

@@ -19,59 +19,23 @@
 
 #pragma once
 
-#include "migration/MigratiorStatus.hpp"
+#include "migration/MigrationInspectorInterface.hpp"
 
 #include <string>
-#include <tuple>
-#include <vector>
 
 namespace migration {
 
 /**
- * @brief The interface for the migration manager. This interface is tend to be implemented for specific database. The
+ * @brief The interface for the migration manager. The migration application layer will use this interface to run the
- * application layer will use this interface to run the migrations.
+ * migrations. Unlike the MigrationInspectorInterface which only provides the status of migration, this interface
+ * contains the acutal migration running method.
  */
-struct MigrationManagerInterface {
+struct MigrationManagerInterface : virtual public MigrationInspectorInterface {
-    virtual ~MigrationManagerInterface() = default;
-
     /**
      * @brief Run the the migration according to the given migrator's name
      */
     virtual void
     runMigration(std::string const&) = 0;
-
-    /**
-     * @brief Get the status of all the migrators
-     * @return A vector of tuple, the first element is the migrator's name, the second element is the status of the
-     */
-    virtual std::vector<std::tuple<std::string, MigratorStatus>>
-    allMigratorsStatusPairs() const = 0;
-
-    /**
-     * @brief Get all registered migrators' names
-     *
-     * @return A vector of migrators' names
-     */
-    virtual std::vector<std::string>
-    allMigratorsNames() const = 0;
-
-    /**
-     * @brief Get the status of a migrator by its name
-     *
-     * @param name The migrator's name
-     * @return The status of the migrator
-     */
-    virtual MigratorStatus
-    getMigratorStatusByName(std::string const& name) const = 0;
-
-    /**
-     * @brief Get the description of a migrator by its name
-     *
-     * @param name The migrator's name
-     * @return The description of the migrator
-     */
-    virtual std::string
-    getMigratorDescriptionByName(std::string const& name) const = 0;
 };
 
 }  // namespace migration

src/migration/README.md

@@ -40,9 +40,11 @@ A migrator satisfies the `MigratorSpec`(impl/Spec.hpp) concept.
 
 It contains:
 
--  A `name` which will be used to identify the migrator. User will refer this migrator in command-line tool by this name. The name needs to be different with other migrators, otherwise a compilation error will be raised.
+- A `kNAME` which will be used to identify the migrator. User will refer this migrator in command-line tool by this name. The name needs to be different with other migrators, otherwise a compilation error will be raised.
 
--  A `description` which is the detail information of the migrator.
+- A `kDESCRIPTION` which is the detail information of the migrator.
+
+- An optional `kCAN_BLOCK_CLIO` which indicates whether the migrator can block the Clio server. If it's absent, the migrator can't block server. If there is a blocking migrator not completed, the Clio server will fail to start.
 
 - A static function `runMigration`, it will be called when user run `--migrate name`. It accepts two parameters: backend, which provides the DB operations interface, and cfg, which provides migration-related configuration. Each migrator can have its own configuration under `.migration` session.
 
@@ -65,8 +67,8 @@ Most indexes are based on either ledger states or transactions. We provide the `
 If you need to do full scan against other table, you can follow below steps:
 - Describe the table which needs full scan in a struct. It has to satisfy the `TableSpec`(cassandra/Spec.hpp) concept, containing static member:
     - Tuple type `Row`, it's the type of each field in a row. The order of types should match what database will return in a row. Key types should come first, followed by other field types sorted in alphabetical order.
-    - `PARTITION_KEY`, it's the name of the partition key of the table.
+    - `kPARTITION_KEY`, it's the name of the partition key of the table.
-    - `TABLE_NAME`
+    - `kTABLE_NAME`
 
 - Inherent from `FullTableScannerAdapterBase`.
 - Implement `onRowRead`, its parameter is the `Row` we defined. It's the callback function when a row is read.

src/migration/cassandra/CassandraMigrationManager.hpp

@@ -19,20 +19,32 @@
 
 #pragma once
 
+#include "data/BackendInterface.hpp"
 #include "migration/cassandra/CassandraMigrationBackend.hpp"
+#include "migration/impl/MigrationInspectorBase.hpp"
 #include "migration/impl/MigrationManagerBase.hpp"
 #include "migration/impl/MigratorsRegister.hpp"
 
-namespace migration::cassandra {
+namespace {
 
 // Register migrators here
 // MigratorsRegister<BackendType, ExampleMigrator>
 template <typename BackendType>
 using CassandraSupportedMigrators = migration::impl::MigratorsRegister<BackendType>;
 
-// Register with MigrationBackend which proceeds the migration
+//  Instantiates with the backend which supports actual migration running
-using MigrationProcesser = CassandraSupportedMigrators<CassandraMigrationBackend>;
+using MigrationProcesser = CassandraSupportedMigrators<migration::cassandra::CassandraMigrationBackend>;
+
+// Instantiates with backend interface, it doesn't support actual migration. But it can be used to inspect the migrators
+// status
+using MigrationQuerier = CassandraSupportedMigrators<data::BackendInterface>;
+
+}  // namespace
+
+namespace migration::cassandra {
+
+using CassandraMigrationInspector = migration::impl::MigrationInspectorBase<MigrationQuerier>;
 
-// The Cassandra migration manager
 using CassandraMigrationManager = migration::impl::MigrationManagerBase<MigrationProcesser>;
+
 }  // namespace migration::cassandra

src/migration/impl/MigrationInspectorBase.hpp

@@ -0,0 +1,121 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2025, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#pragma once
+
+#include "migration/MigrationInspectorInterface.hpp"
+#include "migration/MigratiorStatus.hpp"
+
+#include <memory>
+#include <ranges>
+#include <string>
+#include <tuple>
+#include <vector>
+
+namespace migration::impl {
+
+/**
+ * @brief The migration inspector implementation for Cassandra. It will report the migration status for Cassandra
+ * database.
+ *
+ * @tparam SupportedMigrators The migrators resgister that contains all the migrators
+ */
+template <typename SupportedMigrators>
+class MigrationInspectorBase : virtual public MigrationInspectorInterface {
+protected:
+    SupportedMigrators migrators_;
+
+public:
+    /**
+     * @brief Construct a new Cassandra Migration Inspector object
+     *
+     * @param backend The backend of the Cassandra database
+     */
+    explicit MigrationInspectorBase(std::shared_ptr<typename SupportedMigrators::BackendType> backend)
+        : migrators_{std::move(backend)}
+    {
+    }
+
+    /**
+     * @brief Get the status of all the migrators
+     *
+     * @return A vector of tuple, the first element is the migrator's name, the second element is the status of the
+     * migrator
+     */
+    std::vector<std::tuple<std::string, MigratorStatus>>
+    allMigratorsStatusPairs() const override
+    {
+        return migrators_.getMigratorsStatus();
+    }
+
+    /**
+     * @brief Get the status of a migrator by its name
+     *
+     * @param name The name of the migrator
+     * @return The status of the migrator
+     */
+    MigratorStatus
+    getMigratorStatusByName(std::string const& name) const override
+    {
+        return migrators_.getMigratorStatus(name);
+    }
+
+    /**
+     * @brief Get all registered migrators' names
+     *
+     * @return A vector of string, the names of all the migrators
+     */
+    std::vector<std::string>
+    allMigratorsNames() const override
+    {
+        auto const names = migrators_.getMigratorNames();
+        return std::vector<std::string>{names.begin(), names.end()};
+    }
+
+    /**
+     * @brief Get the description of a migrator by its name
+     *
+     * @param name The name of the migrator
+     * @return The description of the migrator
+     */
+    std::string
+    getMigratorDescriptionByName(std::string const& name) const override
+    {
+        return migrators_.getMigratorDescription(name);
+    }
+
+    /**
+     * @brief Return if there is uncomplete migrator blocking the server
+     *
+     * @return True if server is blocked, false otherwise
+     */
+    bool
+    isBlockingClio() const override
+    {
+        return std::ranges::any_of(migrators_.getMigratorNames(), [&](auto const& migrator) {
+            if (auto canBlock = migrators_.canMigratorBlockClio(migrator); canBlock.has_value() and *canBlock and
+                migrators_.getMigratorStatus(std::string(migrator)) == MigratorStatus::Status::NotMigrated) {
+                return true;
+            }
+            return false;
+        });
+    }
+};
+
+}  // namespace migration::impl

src/migration/impl/MigrationManagerBase.hpp

@@ -20,14 +20,12 @@
 #pragma once
 
 #include "migration/MigrationManagerInterface.hpp"
-#include "migration/MigratiorStatus.hpp"
+#include "migration/impl/MigrationInspectorBase.hpp"
 #include "util/newconfig/ObjectView.hpp"
 
 #include <memory>
 #include <string>
-#include <tuple>
 #include <utility>
-#include <vector>
 
 namespace migration::impl {
 
@@ -38,8 +36,7 @@ namespace migration::impl {
  * @tparam SupportedMigrators The migrators resgister that contains all the migrators
  */
 template <typename SupportedMigrators>
-class MigrationManagerBase : public MigrationManagerInterface {
+class MigrationManagerBase : public MigrationManagerInterface, public MigrationInspectorBase<SupportedMigrators> {
-    SupportedMigrators migrators_;
     // contains only migration related settings
     util::config::ObjectView config_;
 
@@ -54,7 +51,7 @@ public:
         std::shared_ptr<typename SupportedMigrators::BackendType> backend,
         util::config::ObjectView config
     )
-        : migrators_{backend}, config_{std::move(config)}
+        : MigrationInspectorBase<SupportedMigrators>{std::move(backend)}, config_{std::move(config)}
     {
     }
 
@@ -66,55 +63,7 @@ public:
     void
     runMigration(std::string const& name) override
     {
-        migrators_.runMigrator(name, config_);
+        this->migrators_.runMigrator(name, config_);
-    }
-
-    /**
-     * @brief Get the status of all the migrators
-     *
-     * @return A vector of tuple, the first element is the migrator's name, the second element is the status of the
-     * migrator
-     */
-    std::vector<std::tuple<std::string, MigratorStatus>>
-    allMigratorsStatusPairs() const override
-    {
-        return migrators_.getMigratorsStatus();
-    }
-
-    /**
-     * @brief Get the status of a migrator by its name
-     *
-     * @param name The name of the migrator
-     * @return The status of the migrator
-     */
-    MigratorStatus
-    getMigratorStatusByName(std::string const& name) const override
-    {
-        return migrators_.getMigratorStatus(name);
-    }
-
-    /**
-     * @brief Get all registered migrators' names
-     *
-     * @return A vector of string, the names of all the migrators
-     */
-    std::vector<std::string>
-    allMigratorsNames() const override
-    {
-        auto const names = migrators_.getMigratorNames();
-        return std::vector<std::string>{names.begin(), names.end()};
-    }
-
-    /**
-     * @brief Get the description of a migrator by its name
-     *
-     * @param name The name of the migrator
-     * @return The description of the migrator
-     */
-    std::string
-    getMigratorDescriptionByName(std::string const& name) const override
-    {
-        return migrators_.getMigratorDescription(name);
     }
 };
 

src/migration/impl/MigratorsRegister.hpp

@@ -22,6 +22,7 @@
 #include "data/BackendInterface.hpp"
 #include "migration/MigratiorStatus.hpp"
 #include "migration/impl/Spec.hpp"
+#include "util/Assert.hpp"
 #include "util/Concepts.hpp"
 #include "util/log/Logger.hpp"
 #include "util/newconfig/ObjectView.hpp"
@@ -30,10 +31,12 @@
 #include <array>
 #include <iterator>
 #include <memory>
+#include <optional>
 #include <ranges>
 #include <string>
 #include <string_view>
 #include <tuple>
+#include <utility>
 #include <vector>
 
 namespace migration::impl {
@@ -47,6 +50,11 @@ concept MigrationBackend = requires { requires std::same_as<typename MigratorTyp
 template <typename Backend, typename... MigratorType>
 concept BackendMatchAllMigrators = (MigrationBackend<Backend, MigratorType> && ...);
 
+template <typename T>
+concept HasCanBlockClio = requires(T t) {
+    { t.kCAN_BLOCK_CLIO };
+};
+
 /**
  *@brief The register of migrators. It will dispatch the migration to the corresponding migrator. It also
  *hold the shared pointer of backend, which is used by the migrators.
@@ -81,6 +89,23 @@ class MigratorsRegister {
         return (T::kNAME == targetName) ? T::kDESCRIPTION : "";
     }
 
+    template <typename First, typename... Rest>
+    static constexpr bool
+    canBlockClioHelper(std::string_view targetName)
+    {
+        if (targetName == First::kNAME) {
+            if constexpr (HasCanBlockClio<First>) {
+                return First::kCAN_BLOCK_CLIO;
+            }
+            return false;
+        }
+        if constexpr (sizeof...(Rest) > 0) {
+            return canBlockClioHelper<Rest...>(targetName);
+        }
+        ASSERT(false, "The migrator name is not found");
+        std::unreachable();
+    }
+
 public:
     /**
      * @brief The backend type which is used by the migrators
@@ -179,6 +204,27 @@ public:
             return result.empty() ? "No Description" : result;
         }
     }
+
+    /**
+     * @brief Return if the given migrator can block Clio server
+     *
+     * @param name The migrator's name
+     * @return std::nullopt if the migrator name is not found, or a boolean value indicating whether the migrator is
+     * blocking Clio server.
+     */
+    std::optional<bool>
+    canMigratorBlockClio(std::string_view name) const
+    {
+        if constexpr (sizeof...(MigratorType) == 0) {
+            return std::nullopt;
+        } else {
+            auto const migratiors = getMigratorNames();
+            if (std::ranges::find(migratiors, name) == migratiors.end())
+                return std::nullopt;
+
+            return canBlockClioHelper<MigratorType...>(name);
+        }
+    }
 };
 
 }  // namespace migration::impl

tests/common/migration/TestMigrators.hpp

@@ -26,13 +26,10 @@ struct SimpleTestMigrator {
     using Backend = MockMigrationBackend;
     static constexpr auto kNAME = "SimpleTestMigrator";
     static constexpr auto kDESCRIPTION = "The migrator for version 0 -> 1";
-    static void
+    static constexpr auto kCAN_BLOCK_CLIO = true;
-    runMigration(std::shared_ptr<MockMigrationBackend>, util::config::ObjectView const&)
-    {
-    }
 
     static void
-    reset()
+    runMigration(std::shared_ptr<MockMigrationBackend>, util::config::ObjectView const&)
     {
     }
 };
@@ -45,9 +42,16 @@ struct SimpleTestMigrator2 {
     runMigration(std::shared_ptr<MockMigrationBackend>, util::config::ObjectView const&)
     {
     }
+};
+
+struct SimpleTestMigrator3 {
+    using Backend = MockMigrationBackend;
+    static constexpr auto kNAME = "SimpleTestMigrator3";
+    static constexpr auto kDESCRIPTION = "The migrator for version 3 -> 4";
+    static constexpr auto kCAN_BLOCK_CLIO = false;
 
     static void
-    reset()
+    runMigration(std::shared_ptr<MockMigrationBackend>, util::config::ObjectView const&)
     {
     }
 };

tests/unit/CMakeLists.txt

@@ -60,6 +60,8 @@ target_sources(
           migration/cassandra/SpecTests.cpp
           migration/MigratorRegisterTests.cpp
           migration/MigratorStatusTests.cpp
+          migration/MigrationInspectorFactoryTests.cpp
+          migration/MigrationInspectorBaseTests.cpp
           migration/MigrationManagerBaseTests.cpp
           migration/MigrationManagerFactoryTests.cpp
           migration/SpecTests.cpp

tests/unit/migration/MigrationInspectorBaseTests.cpp

@@ -0,0 +1,130 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2025, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+#include "data/BackendInterface.hpp"
+#include "migration/MigratiorStatus.hpp"
+#include "migration/TestMigrators.hpp"
+#include "migration/impl/MigrationManagerBase.hpp"
+#include "migration/impl/MigratorsRegister.hpp"
+#include "util/MockBackendTestFixture.hpp"
+#include "util/MockPrometheus.hpp"
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include <algorithm>
+#include <memory>
+#include <string>
+#include <tuple>
+
+using TestMigratorRegister =
+    migration::impl::MigratorsRegister<data::BackendInterface, SimpleTestMigrator, SimpleTestMigrator2>;
+
+using TestCassandramigrationInspector = migration::impl::MigrationInspectorBase<TestMigratorRegister>;
+
+struct MigrationInspectorBaseTest : public util::prometheus::WithMockPrometheus, public MockBackendTest {
+    MigrationInspectorBaseTest()
+    {
+        migrationInspector_ = std::make_shared<TestCassandramigrationInspector>(backend_);
+    }
+
+protected:
+    std::shared_ptr<TestCassandramigrationInspector> migrationInspector_;
+};
+
+TEST_F(MigrationInspectorBaseTest, AllStatus)
+{
+    EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator", testing::_)).WillOnce(testing::Return("Migrated"));
+    EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator2", testing::_))
+        .WillOnce(testing::Return("NotMigrated"));
+    auto const status = migrationInspector_->allMigratorsStatusPairs();
+    EXPECT_EQ(status.size(), 2);
+    EXPECT_TRUE(
+        std::ranges::find(status, std::make_tuple("SimpleTestMigrator", migration::MigratorStatus::Migrated)) !=
+        status.end()
+    );
+    EXPECT_TRUE(
+        std::ranges::find(status, std::make_tuple("SimpleTestMigrator2", migration::MigratorStatus::NotMigrated)) !=
+        status.end()
+    );
+}
+
+TEST_F(MigrationInspectorBaseTest, AllNames)
+{
+    auto const names = migrationInspector_->allMigratorsNames();
+    EXPECT_EQ(names.size(), 2);
+    EXPECT_EQ(names[0], "SimpleTestMigrator");
+    EXPECT_EQ(names[1], "SimpleTestMigrator2");
+}
+
+TEST_F(MigrationInspectorBaseTest, Description)
+{
+    EXPECT_EQ(migrationInspector_->getMigratorDescriptionByName("unknown"), "No Description");
+    EXPECT_EQ(
+        migrationInspector_->getMigratorDescriptionByName("SimpleTestMigrator"), "The migrator for version 0 -> 1"
+    );
+    EXPECT_EQ(
+        migrationInspector_->getMigratorDescriptionByName("SimpleTestMigrator2"), "The migrator for version 1 -> 2"
+    );
+}
+
+TEST_F(MigrationInspectorBaseTest, getMigratorStatusByName)
+{
+    EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator", testing::_)).WillOnce(testing::Return("Migrated"));
+    EXPECT_EQ(migrationInspector_->getMigratorStatusByName("SimpleTestMigrator"), migration::MigratorStatus::Migrated);
+
+    EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator2", testing::_))
+        .WillOnce(testing::Return("NotMigrated"));
+    EXPECT_EQ(
+        migrationInspector_->getMigratorStatusByName("SimpleTestMigrator2"), migration::MigratorStatus::NotMigrated
+    );
+}
+
+TEST_F(MigrationInspectorBaseTest, oneMigratorBlockingClio)
+{
+    EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator", testing::_))
+        .WillOnce(testing::Return("NotMigrated"));
+    EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator2", testing::_)).Times(0);
+
+    EXPECT_TRUE(migrationInspector_->isBlockingClio());
+}
+
+TEST_F(MigrationInspectorBaseTest, oneMigratorBlockingClioGetMigrated)
+{
+    EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator", testing::_)).WillOnce(testing::Return("Migrated"));
+    EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator2", testing::_)).Times(0);
+    EXPECT_FALSE(migrationInspector_->isBlockingClio());
+}
+
+TEST_F(MigrationInspectorBaseTest, noMigratorBlockingClio)
+{
+    EXPECT_CALL(*backend_, fetchMigratorStatus).Times(0);
+
+    auto const migrations = migration::impl::MigrationInspectorBase<
+        migration::impl::MigratorsRegister<data::BackendInterface, SimpleTestMigrator2, SimpleTestMigrator3>>(backend_);
+    EXPECT_FALSE(migrations.isBlockingClio());
+}
+
+TEST_F(MigrationInspectorBaseTest, isBlockingClioWhenNoMigrator)
+{
+    EXPECT_CALL(*backend_, fetchMigratorStatus).Times(0);
+
+    auto const migrations =
+        migration::impl::MigrationInspectorBase<migration::impl::MigratorsRegister<data::BackendInterface>>(backend_);
+    EXPECT_FALSE(migrations.isBlockingClio());
+}

tests/unit/migration/MigrationInspectorFactoryTests.cpp

@@ -0,0 +1,75 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2025, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include "data/Types.hpp"
+#include "migration/MigrationInspectorFactory.hpp"
+#include "util/MockBackendTestFixture.hpp"
+#include "util/MockPrometheus.hpp"
+#include "util/newconfig/ConfigDefinition.hpp"
+#include "util/newconfig/ConfigValue.hpp"
+#include "util/newconfig/Types.hpp"
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+#include <optional>
+
+using namespace testing;
+
+struct MigrationInspectorFactoryTests : public util::prometheus::WithPrometheus, public MockBackendTest {
+protected:
+    util::config::ClioConfigDefinition const readerConfig_ = util::config::ClioConfigDefinition{
+        {"read_only", util::config::ConfigValue{util::config::ConfigType::Boolean}.defaultValue(true)}
+    };
+};
+
+struct MigrationInspectorFactoryTestsDeathTest : public MigrationInspectorFactoryTests {};
+
+TEST_F(MigrationInspectorFactoryTestsDeathTest, NullBackend)
+{
+    EXPECT_DEATH(migration::makeMigrationInspector(readerConfig_, nullptr), ".*");
+}
+
+TEST_F(MigrationInspectorFactoryTests, NotInitMigrationTableIfReader)
+{
+    EXPECT_CALL(*backend_, hardFetchLedgerRange).Times(0);
+
+    EXPECT_NE(migration::makeMigrationInspector(readerConfig_, backend_), nullptr);
+}
+
+TEST_F(MigrationInspectorFactoryTests, BackendIsWriterAndDBEmpty)
+{
+    EXPECT_CALL(*backend_, hardFetchLedgerRange).WillOnce(Return(std::nullopt));
+
+    util::config::ClioConfigDefinition const writerConfig = util::config::ClioConfigDefinition{
+        {"read_only", util::config::ConfigValue{util::config::ConfigType::Boolean}.defaultValue(false)}
+    };
+    EXPECT_NE(migration::makeMigrationInspector(writerConfig, backend_), nullptr);
+}
+
+TEST_F(MigrationInspectorFactoryTests, BackendIsWriterAndDBNotEmpty)
+{
+    LedgerRange const range{.minSequence = 1, .maxSequence = 5};
+    EXPECT_CALL(*backend_, hardFetchLedgerRange).WillOnce(Return(range));
+
+    util::config::ClioConfigDefinition const writerConfig = util::config::ClioConfigDefinition{
+        {"read_only", util::config::ConfigValue{util::config::ConfigType::Boolean}.defaultValue(false)}
+    };
+    EXPECT_NE(migration::makeMigrationInspector(writerConfig, backend_), nullptr);
+}

tests/unit/migration/MigrationManagerBaseTests.cpp

@@ -54,7 +54,6 @@ struct MigrationManagerBaseTest : public util::prometheus::WithMockPrometheus, p
     MigrationManagerBaseTest()
     {
         auto mockBackendPtr = backend_.operator std::shared_ptr<MockMigrationBackend>();
-        TestMigratorRegister const migratorRegister(mockBackendPtr);
         migrationManager = std::make_shared<TestCassandraMigrationManager>(mockBackendPtr, cfg.getObject("migration"));
     }
 };

tests/unit/migration/MigratorRegisterTests.cpp

@@ -67,8 +67,8 @@ TEST_F(MigratorRegisterTests, EmptyMigratorRegister)
     EXPECT_EQ(migratorRegister.getMigratorDescription("unknown"), "No Description");
 }
 
-using MultipleMigratorRegister =
+using MultipleMigratorRegister = migration::impl::
-    migration::impl::MigratorsRegister<MockMigrationBackend, SimpleTestMigrator, SimpleTestMigrator2>;
+    MigratorsRegister<MockMigrationBackend, SimpleTestMigrator, SimpleTestMigrator2, SimpleTestMigrator3>;
 
 struct MultipleMigratorRegisterTests : public util::prometheus::WithMockPrometheus, public MockMigrationBackendTest {
     std::optional<MultipleMigratorRegister> migratorRegister;
@@ -82,11 +82,11 @@ struct MultipleMigratorRegisterTests : public util::prometheus::WithMockPromethe
 TEST_F(MultipleMigratorRegisterTests, GetMigratorsStatusWhenError)
 {
     EXPECT_CALL(*backend_, fetchMigratorStatus(testing::_, testing::_))
-        .Times(2)
+        .Times(3)
         .WillRepeatedly(testing::Return(std::nullopt));
 
     auto const status = migratorRegister->getMigratorsStatus();
-    EXPECT_EQ(status.size(), 2);
+    EXPECT_EQ(status.size(), 3);
     EXPECT_TRUE(
         std::ranges::find(status, std::make_tuple("SimpleTestMigrator", migration::MigratorStatus::NotMigrated)) !=
         status.end()
@@ -95,16 +95,20 @@ TEST_F(MultipleMigratorRegisterTests, GetMigratorsStatusWhenError)
         std::ranges::find(status, std::make_tuple("SimpleTestMigrator2", migration::MigratorStatus::NotMigrated)) !=
         status.end()
     );
+    EXPECT_TRUE(
+        std::ranges::find(status, std::make_tuple("SimpleTestMigrator3", migration::MigratorStatus::NotMigrated)) !=
+        status.end()
+    );
 }
 
 TEST_F(MultipleMigratorRegisterTests, GetMigratorsStatusWhenReturnInvalidStatus)
 {
     EXPECT_CALL(*backend_, fetchMigratorStatus(testing::_, testing::_))
-        .Times(2)
+        .Times(3)
         .WillRepeatedly(testing::Return("Invalid"));
 
     auto const status = migratorRegister->getMigratorsStatus();
-    EXPECT_EQ(status.size(), 2);
+    EXPECT_EQ(status.size(), 3);
     EXPECT_TRUE(
         std::ranges::find(status, std::make_tuple("SimpleTestMigrator", migration::MigratorStatus::NotMigrated)) !=
         status.end()
@@ -113,6 +117,10 @@ TEST_F(MultipleMigratorRegisterTests, GetMigratorsStatusWhenReturnInvalidStatus)
         std::ranges::find(status, std::make_tuple("SimpleTestMigrator2", migration::MigratorStatus::NotMigrated)) !=
         status.end()
     );
+    EXPECT_TRUE(
+        std::ranges::find(status, std::make_tuple("SimpleTestMigrator3", migration::MigratorStatus::NotMigrated)) !=
+        status.end()
+    );
 }
 
 TEST_F(MultipleMigratorRegisterTests, GetMigratorsStatusWhenOneMigrated)
@@ -120,9 +128,11 @@ TEST_F(MultipleMigratorRegisterTests, GetMigratorsStatusWhenOneMigrated)
     EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator", testing::_)).WillOnce(testing::Return("Migrated"));
     EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator2", testing::_))
         .WillOnce(testing::Return("NotMigrated"));
+    EXPECT_CALL(*backend_, fetchMigratorStatus("SimpleTestMigrator3", testing::_))
+        .WillOnce(testing::Return("NotMigrated"));
 
     auto const status = migratorRegister->getMigratorsStatus();
-    EXPECT_EQ(status.size(), 2);
+    EXPECT_EQ(status.size(), 3);
     EXPECT_TRUE(
         std::ranges::find(status, std::make_tuple("SimpleTestMigrator", migration::MigratorStatus::Migrated)) !=
         status.end()
@@ -131,6 +141,10 @@ TEST_F(MultipleMigratorRegisterTests, GetMigratorsStatusWhenOneMigrated)
         std::ranges::find(status, std::make_tuple("SimpleTestMigrator2", migration::MigratorStatus::NotMigrated)) !=
         status.end()
     );
+    EXPECT_TRUE(
+        std::ranges::find(status, std::make_tuple("SimpleTestMigrator3", migration::MigratorStatus::NotMigrated)) !=
+        status.end()
+    );
 }
 
 TEST_F(MultipleMigratorRegisterTests, GetMigratorStatus)
@@ -158,9 +172,10 @@ TEST_F(MultipleMigratorRegisterTests, GetMigratorStatusWhenError)
 TEST_F(MultipleMigratorRegisterTests, Names)
 {
     auto names = migratorRegister->getMigratorNames();
-    EXPECT_EQ(names.size(), 2);
+    EXPECT_EQ(names.size(), 3);
     EXPECT_TRUE(std::ranges::find(names, "SimpleTestMigrator") != names.end());
     EXPECT_TRUE(std::ranges::find(names, "SimpleTestMigrator2") != names.end());
+    EXPECT_TRUE(std::ranges::find(names, "SimpleTestMigrator3") != names.end());
 }
 
 TEST_F(MultipleMigratorRegisterTests, Description)
@@ -181,3 +196,21 @@ TEST_F(MultipleMigratorRegisterTests, MigrateNormalMigrator)
     EXPECT_CALL(*backend_, writeMigratorStatus("SimpleTestMigrator", "Migrated")).Times(1);
     EXPECT_NO_THROW(migratorRegister->runMigrator("SimpleTestMigrator", gCfg.getObject("migration")));
 }
+
+TEST_F(MultipleMigratorRegisterTests, canBlock)
+{
+    auto canBlock = migratorRegister->canMigratorBlockClio("SimpleTestMigrator");
+    EXPECT_TRUE(canBlock);
+    EXPECT_TRUE(*canBlock);
+
+    canBlock = migratorRegister->canMigratorBlockClio("SimpleTestMigrator2");
+    EXPECT_TRUE(canBlock);
+    EXPECT_FALSE(*canBlock);
+
+    canBlock = migratorRegister->canMigratorBlockClio("SimpleTestMigrator3");
+    EXPECT_TRUE(canBlock);
+    EXPECT_FALSE(*canBlock);
+
+    canBlock = migratorRegister->canMigratorBlockClio("NotAMigrator");
+    EXPECT_FALSE(canBlock);
+}