path: root/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp

/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kSharding

#include "mongo/platform/basic.h"

#include "mongo/db/s/config/sharding_catalog_manager.h"

#include <iomanip>
#include <pcrecpp.h>
#include <set>

#include "mongo/base/status_with.h"
#include "mongo/bson/bsonobj_comparator.h"
#include "mongo/bson/util/bson_extract.h"
#include "mongo/client/connection_string.h"
#include "mongo/client/read_preference.h"
#include "mongo/client/remote_command_targeter.h"
#include "mongo/client/replica_set_monitor.h"
#include "mongo/db/api_parameters.h"
#include "mongo/db/audit.h"
#include "mongo/db/catalog_raii.h"
#include "mongo/db/client.h"
#include "mongo/db/commands/feature_compatibility_version.h"
#include "mongo/db/commands/feature_compatibility_version_parser.h"
#include "mongo/db/commands/set_feature_compatibility_version_gen.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/operation_context.h"
#include "mongo/db/read_write_concern_defaults.h"
#include "mongo/db/repl/hello_gen.h"
#include "mongo/db/repl/repl_client_info.h"
#include "mongo/db/repl/repl_set_config.h"
#include "mongo/db/s/add_shard_cmd_gen.h"
#include "mongo/db/s/add_shard_util.h"
#include "mongo/db/s/sharding_logging.h"
#include "mongo/db/s/type_shard_identity.h"
#include "mongo/db/vector_clock_mutable.h"
#include "mongo/db/wire_version.h"
#include "mongo/executor/task_executor.h"
#include "mongo/logv2/log.h"
#include "mongo/rpc/get_status_from_command_result.h"
#include "mongo/s/catalog/config_server_version.h"
#include "mongo/s/catalog/sharding_catalog_client.h"
#include "mongo/s/catalog/type_database.h"
#include "mongo/s/catalog/type_shard.h"
#include "mongo/s/client/shard.h"
#include "mongo/s/client/shard_registry.h"
#include "mongo/s/cluster_identity_loader.h"
#include "mongo/s/database_version.h"
#include "mongo/s/grid.h"
#include "mongo/s/write_ops/batched_command_request.h"
#include "mongo/s/write_ops/batched_command_response.h"
#include "mongo/util/fail_point.h"
#include "mongo/util/scopeguard.h"
#include "mongo/util/str.h"
#include "mongo/util/version/releases.h"

namespace mongo {
namespace {

using CallbackHandle = executor::TaskExecutor::CallbackHandle;
using CallbackArgs = executor::TaskExecutor::CallbackArgs;
using RemoteCommandCallbackArgs = executor::TaskExecutor::RemoteCommandCallbackArgs;
using RemoteCommandCallbackFn = executor::TaskExecutor::RemoteCommandCallbackFn;

const ReadPreferenceSetting kConfigReadSelector(ReadPreference::Nearest, TagSet{});

/**
 * Generates a unique name to be given to a newly added shard.
 */
StatusWith<std::string> generateNewShardName(OperationContext* opCtx) {
    BSONObjBuilder shardNameRegex;
    shardNameRegex.appendRegex(ShardType::name(), "^shard");

    auto findStatus = Grid::get(opCtx)->shardRegistry()->getConfigShard()->exhaustiveFindOnConfig(
        opCtx,
        kConfigReadSelector,
        repl::ReadConcernLevel::kLocalReadConcern,
        ShardType::ConfigNS,
        shardNameRegex.obj(),
        BSON(ShardType::name() << -1),
        1);
    if (!findStatus.isOK()) {
        return findStatus.getStatus();
    }

    const auto& docs = findStatus.getValue().docs;

    int count = 0;
    if (!docs.empty()) {
        const auto shardStatus = ShardType::fromBSON(docs.front());
        if (!shardStatus.isOK()) {
            return shardStatus.getStatus();
        }

        std::istringstream is(shardStatus.getValue().getName().substr(5));
        is >> count;
        count++;
    }

    // TODO: fix so that we can have more than 10000 automatically generated shard names
    if (count < 9999) {
        std::stringstream ss;
        ss << "shard" << std::setfill('0') << std::setw(4) << count;
        return ss.str();
    }

    return Status(ErrorCodes::OperationFailed, "unable to generate new shard name");
}

}  // namespace

StatusWith<Shard::CommandResponse> ShardingCatalogManager::_runCommandForAddShard(
    OperationContext* opCtx,
    RemoteCommandTargeter* targeter,
    StringData dbName,
    const BSONObj& cmdObj) {
    auto swHost = targeter->findHost(opCtx, ReadPreferenceSetting{ReadPreference::PrimaryOnly});
    if (!swHost.isOK()) {
        return swHost.getStatus();
    }
    auto host = std::move(swHost.getValue());

    executor::RemoteCommandRequest request(
        host, dbName.toString(), cmdObj, rpc::makeEmptyMetadata(), opCtx, Seconds(60));

    executor::RemoteCommandResponse response =
        Status(ErrorCodes::InternalError, "Internal error running command");

    auto swCallbackHandle = _executorForAddShard->scheduleRemoteCommand(
        request, [&response](const executor::TaskExecutor::RemoteCommandCallbackArgs& args) {
            response = args.response;
        });
    if (!swCallbackHandle.isOK()) {
        return swCallbackHandle.getStatus();
    }

    // Block until the command is carried out
    _executorForAddShard->wait(swCallbackHandle.getValue());

    if (response.status == ErrorCodes::ExceededTimeLimit) {
        LOGV2(21941,
              "Operation timed out with {error}",
              "Operation timed out",
              "error"_attr = redact(response.status));
    }

    if (!response.isOK()) {
        if (!Shard::shouldErrorBePropagated(response.status.code())) {
            return {ErrorCodes::OperationFailed,
                    str::stream() << "failed to run command " << cmdObj
                                  << " when attempting to add shard "
                                  << targeter->connectionString().toString()
                                  << causedBy(response.status)};
        }
        return response.status;
    }

    BSONObj result = response.data.getOwned();

    Status commandStatus = getStatusFromCommandResult(result);
    if (!Shard::shouldErrorBePropagated(commandStatus.code())) {
        commandStatus = {
            ErrorCodes::OperationFailed,
            str::stream() << "failed to run command " << cmdObj << " when attempting to add shard "
                          << targeter->connectionString().toString() << causedBy(commandStatus)};
    }

    Status writeConcernStatus = getWriteConcernStatusFromCommandResult(result);
    if (!Shard::shouldErrorBePropagated(writeConcernStatus.code())) {
        writeConcernStatus = {ErrorCodes::OperationFailed,
                              str::stream() << "failed to satisfy writeConcern for command "
                                            << cmdObj << " when attempting to add shard "
                                            << targeter->connectionString().toString()
                                            << causedBy(writeConcernStatus)};
    }

    return Shard::CommandResponse(std::move(host),
                                  std::move(result),
                                  std::move(commandStatus),
                                  std::move(writeConcernStatus));
}

StatusWith<boost::optional<ShardType>> ShardingCatalogManager::_checkIfShardExists(
    OperationContext* opCtx,
    const ConnectionString& proposedShardConnectionString,
    const std::string* proposedShardName,
    long long proposedShardMaxSize) {
    // Check whether any host in the connection is already part of the cluster.
    const auto existingShards = Grid::get(opCtx)->catalogClient()->getAllShards(
        opCtx, repl::ReadConcernLevel::kLocalReadConcern);
    if (!existingShards.isOK()) {
        return existingShards.getStatus().withContext(
            "Failed to load existing shards during addShard");
    }

    // Now check if this shard already exists - if it already exists *with the same options* then
    // the addShard request can return success early without doing anything more.
    for (const auto& existingShard : existingShards.getValue().value) {
        auto swExistingShardConnStr = ConnectionString::parse(existingShard.getHost());
        if (!swExistingShardConnStr.isOK()) {
            return swExistingShardConnStr.getStatus();
        }
        auto existingShardConnStr = std::move(swExistingShardConnStr.getValue());

        // Function for determining if the options for the shard that is being added match the
        // options of an existing shard that conflicts with it.
        auto shardsAreEquivalent = [&]() {
            if (proposedShardName && *proposedShardName != existingShard.getName()) {
                return false;
            }
            if (proposedShardConnectionString.type() != existingShardConnStr.type()) {
                return false;
            }
            if (proposedShardConnectionString.type() ==
                    ConnectionString::ConnectionType::kReplicaSet &&
                proposedShardConnectionString.getSetName() != existingShardConnStr.getSetName()) {
                return false;
            }
            if (proposedShardMaxSize != existingShard.getMaxSizeMB()) {
                return false;
            }
            return true;
        };

        if (existingShardConnStr.type() == ConnectionString::ConnectionType::kReplicaSet &&
            proposedShardConnectionString.type() == ConnectionString::ConnectionType::kReplicaSet &&
            existingShardConnStr.getSetName() == proposedShardConnectionString.getSetName()) {
            // An existing shard has the same replica set name as the shard being added.
            // If the options aren't the same, then this is an error,
            // but if the options match then the addShard operation should be immediately
            // considered a success and terminated.
            if (shardsAreEquivalent()) {
                return {existingShard};
            } else {
                return {ErrorCodes::IllegalOperation,
                        str::stream() << "A shard already exists containing the replica set '"
                                      << existingShardConnStr.getSetName() << "'"};
            }
        }

        for (const auto& existingHost : existingShardConnStr.getServers()) {
            // Look if any of the hosts in the existing shard are present within the shard trying
            // to be added.
            for (const auto& addingHost : proposedShardConnectionString.getServers()) {
                if (existingHost == addingHost) {
                    // At least one of the hosts in the shard being added already exists in an
                    // existing shard.  If the options aren't the same, then this is an error,
                    // but if the options match then the addShard operation should be immediately
                    // considered a success and terminated.
                    if (shardsAreEquivalent()) {
                        return {existingShard};
                    } else {
                        return {ErrorCodes::IllegalOperation,
                                str::stream() << "'" << addingHost.toString() << "' "
                                              << "is already a member of the existing shard '"
                                              << existingShard.getHost() << "' ("
                                              << existingShard.getName() << ")."};
                    }
                }
            }
        }

        if (proposedShardName && *proposedShardName == existingShard.getName()) {
            // If we get here then we're trying to add a shard with the same name as an existing
            // shard, but there was no overlap in the hosts between the existing shard and the
            // proposed connection string for the new shard.
            return {ErrorCodes::IllegalOperation,
                    str::stream() << "A shard named " << *proposedShardName << " already exists"};
        }
    }

    return {boost::none};
}

StatusWith<ShardType> ShardingCatalogManager::_validateHostAsShard(
    OperationContext* opCtx,
    std::shared_ptr<RemoteCommandTargeter> targeter,
    const std::string* shardProposedName,
    const ConnectionString& connectionString) {
    auto swCommandResponse = _runCommandForAddShard(
        opCtx, targeter.get(), NamespaceString::kAdminDb, BSON("isMaster" << 1));
    if (swCommandResponse.getStatus() == ErrorCodes::IncompatibleServerVersion) {
        return swCommandResponse.getStatus().withReason(
            str::stream() << "Cannot add " << connectionString.toString()
                          << " as a shard because its binary version is not compatible with "
                             "the cluster's featureCompatibilityVersion.");
    } else if (!swCommandResponse.isOK()) {
        return swCommandResponse.getStatus();
    }

    // Check for a command response error
    auto resIsMasterStatus = std::move(swCommandResponse.getValue().commandStatus);
    if (!resIsMasterStatus.isOK()) {
        return resIsMasterStatus.withContext(str::stream()
                                             << "Error running isMaster against "
                                             << targeter->connectionString().toString());
    }

    auto resIsMaster = std::move(swCommandResponse.getValue().response);

    // Fail if the node being added is a mongos.
    const std::string msg = resIsMaster.getStringField("msg").toString();
    if (msg == "isdbgrid") {
        return {ErrorCodes::IllegalOperation, "cannot add a mongos as a shard"};
    }

    // Extract the maxWireVersion so we can verify that the node being added has a binary version
    // greater than or equal to the cluster's featureCompatibilityVersion. We expect an incompatible
    // binary node to be unable to communicate, returning an IncompatibleServerVersion error,
    // because of our internal wire version protocol. So we can safely invariant here that the node
    // is compatible.
    long long maxWireVersion;
    Status status = bsonExtractIntegerField(resIsMaster, "maxWireVersion", &maxWireVersion);
    if (!status.isOK()) {
        return status.withContext(str::stream() << "isMaster returned invalid 'maxWireVersion' "
                                                << "field when attempting to add "
                                                << connectionString.toString() << " as a shard");
    }

    // Check whether there is a master. If there isn't, the replica set may not have been
    // initiated. If the connection is a standalone, it will return true for isMaster.
    bool isMaster;
    status = bsonExtractBooleanField(resIsMaster, "ismaster", &isMaster);
    if (!status.isOK()) {
        return status.withContext(str::stream() << "isMaster returned invalid 'ismaster' "
                                                << "field when attempting to add "
                                                << connectionString.toString() << " as a shard");
    }
    if (!isMaster) {
        return {ErrorCodes::NotWritablePrimary,
                str::stream()
                    << connectionString.toString()
                    << " does not have a master. If this is a replica set, ensure that it has a"
                    << " healthy primary and that the set has been properly initiated."};
    }

    const std::string providedSetName = connectionString.getSetName();
    const std::string foundSetName = resIsMaster["setName"].str();

    // Make sure the specified replica set name (if any) matches the actual shard's replica set
    if (providedSetName.empty() && !foundSetName.empty()) {
        return {ErrorCodes::OperationFailed,
                str::stream() << "host is part of set " << foundSetName << "; "
                              << "use replica set url format "
                              << "<setname>/<server1>,<server2>, ..."};
    }

    if (!providedSetName.empty() && foundSetName.empty()) {
        return {ErrorCodes::OperationFailed,
                str::stream() << "host did not return a set name; "
                              << "is the replica set still initializing? " << resIsMaster};
    }

    // Make sure the set name specified in the connection string matches the one where its hosts
    // belong into
    if (!providedSetName.empty() && (providedSetName != foundSetName)) {
        return {ErrorCodes::OperationFailed,
                str::stream() << "the provided connection string (" << connectionString.toString()
                              << ") does not match the actual set name " << foundSetName};
    }

    // Is it a config server?
    if (resIsMaster.hasField("configsvr")) {
        return {ErrorCodes::OperationFailed,
                str::stream() << "Cannot add " << connectionString.toString()
                              << " as a shard since it is a config server"};
    }

    if (resIsMaster.hasField(HelloCommandReply::kIsImplicitDefaultMajorityWCFieldName) &&
        !resIsMaster.getBoolField(HelloCommandReply::kIsImplicitDefaultMajorityWCFieldName) &&
        !ReadWriteConcernDefaults::get(opCtx).isCWWCSet(opCtx)) {
        return {
            ErrorCodes::OperationFailed,
            str::stream()
                << "Cannot add " << connectionString.toString()
                << " as a shard since the implicit default write concern on this shard is set to "
                   "{w : 1}, because number of arbiters in the shard's configuration caused the "
                   "number of writable voting members not to be strictly more than the voting "
                   "majority. Change the shard configuration or set the cluster-wide write concern "
                   "using the setDefaultRWConcern command and try again."};
    }

    if (resIsMaster.hasField(HelloCommandReply::kCwwcFieldName)) {
        auto cwwcOnShard = WriteConcernOptions::parse(
                               resIsMaster.getObjectField(HelloCommandReply::kCwwcFieldName))
                               .getValue()
                               .toBSON();

        auto cachedCWWC = ReadWriteConcernDefaults::get(opCtx).getCWWC(opCtx);
        if (!cachedCWWC) {
            return {ErrorCodes::OperationFailed,
                    str::stream() << "Cannot add " << connectionString.toString()
                                  << " as a shard since the cluster-wide write concern is set on "
                                     "the shard and not set on the cluster. Set the CWWC on the "
                                     "cluster to the same CWWC as the shard and try again."
                                  << " The CWWC on the shard is (" << cwwcOnShard << ")."};
        }

        auto cwwcOnConfig = cachedCWWC.get().toBSON();
        BSONObjComparator comparator(
            BSONObj(), BSONObjComparator::FieldNamesMode::kConsider, nullptr);
        if (comparator.compare(cwwcOnShard, cwwcOnConfig) != 0) {
            return {
                ErrorCodes::OperationFailed,
                str::stream()
                    << "Cannot add " << connectionString.toString()
                    << " as a shard since the cluster-wide write concern set on the shard doesn't "
                       "match the one set on the cluster. Make sure they match and try again."
                    << " The CWWC on the shard is (" << cwwcOnShard
                    << "), and the CWWC on the cluster is (" << cwwcOnConfig << ")."};
        }
    }

    // If the shard is part of a replica set, make sure all the hosts mentioned in the connection
    // string are part of the set. It is fine if not all members of the set are mentioned in the
    // connection string, though.
    if (!providedSetName.empty()) {
        std::set<std::string> hostSet;

        BSONObjIterator iter(resIsMaster["hosts"].Obj());
        while (iter.more()) {
            hostSet.insert(iter.next().String());  // host:port
        }

        if (resIsMaster["passives"].isABSONObj()) {
            BSONObjIterator piter(resIsMaster["passives"].Obj());
            while (piter.more()) {
                hostSet.insert(piter.next().String());  // host:port
            }
        }

        if (resIsMaster["arbiters"].isABSONObj()) {
            BSONObjIterator piter(resIsMaster["arbiters"].Obj());
            while (piter.more()) {
                hostSet.insert(piter.next().String());  // host:port
            }
        }

        for (const auto& hostEntry : connectionString.getServers()) {
            const auto& host = hostEntry.toString();  // host:port
            if (hostSet.find(host) == hostSet.end()) {
                return {ErrorCodes::OperationFailed,
                        str::stream() << "in seed list " << connectionString.toString() << ", host "
                                      << host << " does not belong to replica set " << foundSetName
                                      << "; found " << resIsMaster.toString()};
            }
        }
    }

    std::string actualShardName;

    if (shardProposedName) {
        actualShardName = *shardProposedName;
    } else if (!foundSetName.empty()) {
        // Default it to the name of the replica set
        actualShardName = foundSetName;
    }

    // Disallow adding shard replica set with name 'config'
    if (actualShardName == NamespaceString::kConfigDb) {
        return {ErrorCodes::BadValue, "use of shard replica set with name 'config' is not allowed"};
    }

    // Retrieve the most up to date connection string that we know from the replica set monitor (if
    // this is a replica set shard, otherwise it will be the same value as connectionString).
    ConnectionString actualShardConnStr = targeter->connectionString();

    ShardType shard;
    shard.setName(actualShardName);
    shard.setHost(actualShardConnStr.toString());
    shard.setState(ShardType::ShardState::kShardAware);

    return shard;
}

Status ShardingCatalogManager::_dropSessionsCollection(
    OperationContext* opCtx, std::shared_ptr<RemoteCommandTargeter> targeter) {

    BSONObjBuilder builder;
    builder.append("drop", NamespaceString::kLogicalSessionsNamespace.coll());
    {
        BSONObjBuilder wcBuilder(builder.subobjStart("writeConcern"));
        wcBuilder.append("w", "majority");
    }

    auto swCommandResponse = _runCommandForAddShard(
        opCtx, targeter.get(), NamespaceString::kLogicalSessionsNamespace.db(), builder.done());
    if (!swCommandResponse.isOK()) {
        return swCommandResponse.getStatus();
    }

    auto cmdStatus = std::move(swCommandResponse.getValue().commandStatus);
    if (!cmdStatus.isOK() && cmdStatus.code() != ErrorCodes::NamespaceNotFound) {
        return cmdStatus;
    }

    return Status::OK();
}

StatusWith<std::vector<std::string>> ShardingCatalogManager::_getDBNamesListFromShard(
    OperationContext* opCtx, std::shared_ptr<RemoteCommandTargeter> targeter) {

    auto swCommandResponse =
        _runCommandForAddShard(opCtx,
                               targeter.get(),
                               NamespaceString::kAdminDb,
                               BSON("listDatabases" << 1 << "nameOnly" << true));
    if (!swCommandResponse.isOK()) {
        return swCommandResponse.getStatus();
    }

    auto cmdStatus = std::move(swCommandResponse.getValue().commandStatus);
    if (!cmdStatus.isOK()) {
        return cmdStatus;
    }

    auto cmdResult = std::move(swCommandResponse.getValue().response);

    std::vector<std::string> dbNames;

    for (const auto& dbEntry : cmdResult["databases"].Obj()) {
        const auto& dbName = dbEntry["name"].String();

        if (!(dbName == NamespaceString::kAdminDb || dbName == NamespaceString::kLocalDb ||
              dbName == NamespaceString::kConfigDb)) {
            dbNames.push_back(dbName);
        }
    }

    return dbNames;
}

StatusWith<std::string> ShardingCatalogManager::addShard(
    OperationContext* opCtx,
    const std::string* shardProposedName,
    const ConnectionString& shardConnectionString,
    const long long maxSize) {
    if (!shardConnectionString) {
        return {ErrorCodes::BadValue, "Invalid connection string"};
    }

    if (shardProposedName && shardProposedName->empty()) {
        return {ErrorCodes::BadValue, "shard name cannot be empty"};
    }

    const auto shardRegistry = Grid::get(opCtx)->shardRegistry();

    // Only one addShard operation can be in progress at a time.
    Lock::ExclusiveLock lk(opCtx->lockState(), _kShardMembershipLock);

    // Check if this shard has already been added (can happen in the case of a retry after a network
    // error, for example) and thus this addShard request should be considered a no-op.
    auto existingShard =
        _checkIfShardExists(opCtx, shardConnectionString, shardProposedName, maxSize);
    if (!existingShard.isOK()) {
        return existingShard.getStatus();
    }
    if (existingShard.getValue()) {
        // These hosts already belong to an existing shard, so report success and terminate the
        // addShard request.  Make sure to set the last optime for the client to the system last
        // optime so that we'll still wait for replication so that this state is visible in the
        // committed snapshot.
        repl::ReplClientInfo::forClient(opCtx->getClient()).setLastOpToSystemLastOpTime(opCtx);
        return existingShard.getValue()->getName();
    }

    const std::shared_ptr<Shard> shard{shardRegistry->createConnection(shardConnectionString)};
    auto targeter = shard->getTargeter();

    ScopeGuard stopMonitoringGuard([&] {
        if (shardConnectionString.type() == ConnectionString::ConnectionType::kReplicaSet) {
            // This is a workaround for the case were we could have some bad shard being
            // requested to be added and we put that bad connection string on the global replica set
            // monitor registry. It needs to be cleaned up so that when a correct replica set is
            // added, it will be recreated.
            ReplicaSetMonitor::remove(shardConnectionString.getSetName());
        }
    });

    // Validate the specified connection string may serve as shard at all
    auto shardStatus =
        _validateHostAsShard(opCtx, targeter, shardProposedName, shardConnectionString);
    if (!shardStatus.isOK()) {
        return shardStatus.getStatus();
    }
    ShardType& shardType = shardStatus.getValue();

    // Check that none of the existing shard candidate's dbs exist already
    auto dbNamesStatus = _getDBNamesListFromShard(opCtx, targeter);
    if (!dbNamesStatus.isOK()) {
        return dbNamesStatus.getStatus();
    }

    for (const auto& dbName : dbNamesStatus.getValue()) {
        try {
            auto dbt = Grid::get(opCtx)->catalogClient()->getDatabase(
                opCtx, dbName, repl::ReadConcernLevel::kLocalReadConcern);
            return Status(ErrorCodes::OperationFailed,
                          str::stream() << "can't add shard "
                                        << "'" << shardConnectionString.toString() << "'"
                                        << " because a local database '" << dbName
                                        << "' exists in another " << dbt.getPrimary());
        } catch (const ExceptionFor<ErrorCodes::NamespaceNotFound>&) {
        }
    }

    // Check that the shard candidate does not have a local config.system.sessions collection
    auto res = _dropSessionsCollection(opCtx, targeter);
    if (!res.isOK()) {
        return res.withContext(
            "can't add shard with a local copy of config.system.sessions, please drop this "
            "collection from the shard manually and try again.");
    }

    // If a name for a shard wasn't provided, generate one
    if (shardType.getName().empty()) {
        auto result = generateNewShardName(opCtx);
        if (!result.isOK()) {
            return result.getStatus();
        }
        shardType.setName(result.getValue());
    }

    if (maxSize > 0) {
        shardType.setMaxSizeMB(maxSize);
    }

    // Helper function that runs a command on the to-be shard and returns the status
    auto runCmdOnNewShard = [this, &opCtx, &targeter](const BSONObj& cmd) -> Status {
        auto swCommandResponse =
            _runCommandForAddShard(opCtx, targeter.get(), NamespaceString::kAdminDb, cmd);
        if (!swCommandResponse.isOK()) {
            return swCommandResponse.getStatus();
        }
        // Grabs the underlying status from a StatusWith object by taking the first
        // non-OK status, if there is one. This is needed due to the semantics of
        // _runCommandForAddShard.
        auto commandResponse = std::move(swCommandResponse.getValue());
        BatchedCommandResponse batchResponse;
        return Shard::CommandResponse::processBatchWriteResponse(commandResponse, &batchResponse);
    };

    AddShard addShardCmd = add_shard_util::createAddShardCmd(opCtx, shardType.getName());

    // Use the _addShard command to add the shard, which in turn inserts a shardIdentity document
    // into the shard and triggers sharding state initialization.
    auto addShardStatus = runCmdOnNewShard(addShardCmd.toBSON({}));
    if (!addShardStatus.isOK()) {
        return addShardStatus;
    }

    {
        // Keep the FCV stable across checking the FCV, sending setFCV to the new shard and writing
        // the entry for the new shard to config.shards. This ensures the FCV doesn't change after
        // we send setFCV to the new shard, but before we write its entry to config.shards.
        //
        // NOTE: We don't use a Global IX lock here, because we don't want to hold the global lock
        // while blocking on the network).
        FixedFCVRegion fcvRegion(opCtx);

        uassert(5563603,
                "Cannot add shard while in upgrading/downgrading FCV state",
                !fcvRegion->isUpgradingOrDowngrading());

        // (Generic FCV reference): These FCV checks should exist across LTS binary versions.
        invariant(fcvRegion == multiversion::GenericFCV::kLatest ||
                  fcvRegion == multiversion::GenericFCV::kLastContinuous ||
                  fcvRegion == multiversion::GenericFCV::kLastLTS);

        SetFeatureCompatibilityVersion setFcvCmd(fcvRegion->getVersion());
        setFcvCmd.setDbName(NamespaceString::kAdminDb);
        setFcvCmd.setFromConfigServer(true);

        auto versionResponse =
            _runCommandForAddShard(opCtx,
                                   targeter.get(),
                                   NamespaceString::kAdminDb,
                                   setFcvCmd.toBSON(BSON(WriteConcernOptions::kWriteConcernField
                                                         << opCtx->getWriteConcern().toBSON())));
        if (!versionResponse.isOK()) {
            return versionResponse.getStatus();
        }

        if (!versionResponse.getValue().commandStatus.isOK()) {
            return versionResponse.getValue().commandStatus;
        }

        // Tick clusterTime to get a new topologyTime for this mutation of the topology.
        auto newTopologyTime = VectorClockMutable::get(opCtx)->tickClusterTime(1);

        shardType.setTopologyTime(newTopologyTime.asTimestamp());

        LOGV2(21942,
              "Going to insert new entry for shard into config.shards: {shardType}",
              "Going to insert new entry for shard into config.shards",
              "shardType"_attr = shardType.toString());

        Status result = Grid::get(opCtx)->catalogClient()->insertConfigDocument(
            opCtx,
            ShardType::ConfigNS,
            shardType.toBSON(),
            ShardingCatalogClient::kLocalWriteConcern);
        if (!result.isOK()) {
            LOGV2(21943,
                  "Error adding shard: {shardType} err: {error}",
                  "Error adding shard",
                  "shardType"_attr = shardType.toBSON(),
                  "error"_attr = result.reason());
            return result;
        }

        // Add all databases which were discovered on the new shard
        for (const auto& dbName : dbNamesStatus.getValue()) {
            const auto now = VectorClock::get(opCtx)->getTime();
            const auto clusterTime = now.clusterTime().asTimestamp();

            DatabaseType dbt(
                dbName, shardType.getName(), false, DatabaseVersion(UUID::gen(), clusterTime));

            {
                const auto status = Grid::get(opCtx)->catalogClient()->updateConfigDocument(
                    opCtx,
                    DatabaseType::ConfigNS,
                    BSON(DatabaseType::name(dbName)),
                    dbt.toBSON(),
                    true,
                    ShardingCatalogClient::kLocalWriteConcern);
                if (!status.isOK()) {
                    LOGV2(21944,
                          "Adding shard {connectionString} even though could not add database {db}",
                          "Adding shard even though we could not add database",
                          "connectionString"_attr = shardConnectionString.toString(),
                          "db"_attr = dbName);
                }
            }
        }
    }

    // Record in changelog
    BSONObjBuilder shardDetails;
    shardDetails.append("name", shardType.getName());
    shardDetails.append("host", shardConnectionString.toString());

    ShardingLogging::get(opCtx)->logChange(
        opCtx, "addShard", "", shardDetails.obj(), ShardingCatalogClient::kMajorityWriteConcern);

    // Ensure the added shard is visible to this process.
    shardRegistry->reload(opCtx);
    if (!shardRegistry->getShard(opCtx, shardType.getName()).isOK()) {
        return {ErrorCodes::OperationFailed,
                "Could not find shard metadata for shard after adding it. This most likely "
                "indicates that the shard was removed immediately after it was added."};
    }

    stopMonitoringGuard.dismiss();

    return shardType.getName();
}

BSONObj makeCommitRemoveShardCommand(const std::string& removedShardName,
                                     const std::string& controlShardName,
                                     const Timestamp& newTopologyTime) {
    // Remove removeShard's document.
    BSONArrayBuilder updates;
    {
        BSONObjBuilder op;
        op.append("op", "d");
        op.appendBool("b", false);  // No upserting
        op.append("ns", ShardType::ConfigNS.ns());

        BSONObjBuilder n(op.subobjStart("o"));
        n.append(ShardType::name(), removedShardName);
        n.done();

        updates.append(op.obj());
    }

    // Update controlShard's topologyTime.
    {
        BSONObjBuilder op;
        op.append("op", "u");
        op.appendBool("b", false);
        op.append("ns", ShardType::ConfigNS.ns());

        BSONObjBuilder n(op.subobjStart("o"));
        n.append("$set", BSON(ShardType::topologyTime() << newTopologyTime));
        n.done();

        BSONObjBuilder q(op.subobjStart("o2"));
        q.append(ShardType::name(), controlShardName);
        q.done();

        updates.append(op.obj());
    }

    return BSON("applyOps" << updates.arr() << "alwaysUpsert" << false << "writeConcern"
                           << ShardingCatalogClient::kLocalWriteConcern.toBSON());
}

RemoveShardProgress ShardingCatalogManager::removeShard(OperationContext* opCtx,
                                                        const ShardId& shardId) {
    const auto name = shardId.toString();
    audit::logRemoveShard(opCtx->getClient(), name);

    const auto configShard = Grid::get(opCtx)->shardRegistry()->getConfigShard();

    Lock::ExclusiveLock shardLock(opCtx->lockState(), _kShardMembershipLock);

    auto findShardResponse = uassertStatusOK(
        configShard->exhaustiveFindOnConfig(opCtx,
                                            kConfigReadSelector,
                                            repl::ReadConcernLevel::kLocalReadConcern,
                                            ShardType::ConfigNS,
                                            BSON(ShardType::name() << name),
                                            BSONObj(),
                                            1));
    uassert(ErrorCodes::ShardNotFound,
            str::stream() << "Shard " << shardId << " does not exist",
            !findShardResponse.docs.empty());
    const auto shard = uassertStatusOK(ShardType::fromBSON(findShardResponse.docs[0]));

    // Find how many *other* shards exist, which are *not* currently draining
    const auto countOtherNotDrainingShards = uassertStatusOK(_runCountCommandOnConfig(
        opCtx,
        ShardType::ConfigNS,
        BSON(ShardType::name() << NE << name << ShardType::draining.ne(true))));
    uassert(ErrorCodes::IllegalOperation,
            "Operation not allowed because it would remove the last shard",
            countOtherNotDrainingShards > 0);

    // Ensure there are no non-empty zones that only belong to this shard
    for (auto& zoneName : shard.getTags()) {
        auto isRequiredByZone = uassertStatusOK(
            _isShardRequiredByZoneStillInUse(opCtx, kConfigReadSelector, name, zoneName));
        uassert(ErrorCodes::ZoneStillInUse,
                str::stream()
                    << "Operation not allowed because it would remove the only shard for zone "
                    << zoneName << " which has a chunk range is associated with it",
                !isRequiredByZone);
    }

    // Figure out if shard is already draining
    const bool isShardCurrentlyDraining =
        uassertStatusOK(_runCountCommandOnConfig(
            opCtx,
            ShardType::ConfigNS,
            BSON(ShardType::name() << name << ShardType::draining(true)))) > 0;

    auto* const catalogClient = Grid::get(opCtx)->catalogClient();

    if (!isShardCurrentlyDraining) {
        LOGV2(21945,
              "Going to start draining shard: {shardId}",
              "Going to start draining shard",
              "shardId"_attr = name);

        // Record start in changelog
        uassertStatusOK(ShardingLogging::get(opCtx)->logChangeChecked(
            opCtx,
            "removeShard.start",
            "",
            BSON("shard" << name),
            ShardingCatalogClient::kLocalWriteConcern));

        uassertStatusOKWithContext(
            catalogClient->updateConfigDocument(opCtx,
                                                ShardType::ConfigNS,
                                                BSON(ShardType::name() << name),
                                                BSON("$set" << BSON(ShardType::draining(true))),
                                                false,
                                                ShardingCatalogClient::kLocalWriteConcern),
            "error starting removeShard");

        return {RemoveShardProgress::STARTED,
                boost::optional<RemoveShardProgress::DrainingShardUsage>(boost::none)};
    }

    shardLock.unlock();

    // Draining has already started, now figure out how many chunks and databases are still on the
    // shard.
    const auto chunkCount = uassertStatusOK(
        _runCountCommandOnConfig(opCtx, ChunkType::ConfigNS, BSON(ChunkType::shard(name))));

    const auto databaseCount = uassertStatusOK(
        _runCountCommandOnConfig(opCtx, DatabaseType::ConfigNS, BSON(DatabaseType::primary(name))));

    const auto jumboCount = uassertStatusOK(_runCountCommandOnConfig(
        opCtx, ChunkType::ConfigNS, BSON(ChunkType::shard(name) << ChunkType::jumbo(true))));

    if (chunkCount > 0 || databaseCount > 0) {
        // Still more draining to do
        LOGV2(21946,
              "removeShard: draining chunkCount {chunkCount}; databaseCount {databaseCount}; "
              "jumboCount {jumboCount}",
              "removeShard: draining",
              "chunkCount"_attr = chunkCount,
              "databaseCount"_attr = databaseCount,
              "jumboCount"_attr = jumboCount);

        return {RemoveShardProgress::ONGOING,
                boost::optional<RemoveShardProgress::DrainingShardUsage>(
                    {chunkCount, databaseCount, jumboCount})};
    }

    // Draining is done, now finish removing the shard.
    LOGV2(
        21949, "Going to remove shard: {shardId}", "Going to remove shard", "shardId"_attr = name);

    // Find a controlShard to be updated.
    auto controlShardQueryStatus =
        configShard->exhaustiveFindOnConfig(opCtx,
                                            ReadPreferenceSetting{ReadPreference::PrimaryOnly},
                                            repl::ReadConcernLevel::kLocalReadConcern,
                                            ShardType::ConfigNS,
                                            BSON(ShardType::name.ne(name)),
                                            {},
                                            1);
    auto controlShardResponse = uassertStatusOK(controlShardQueryStatus);
    // Since it's not possible to remove the last shard, there should always be a control shard.
    uassert(4740601,
            "unable to find a controlShard to update during removeShard",
            !controlShardResponse.docs.empty());
    const auto controlShardStatus = ShardType::fromBSON(controlShardResponse.docs.front());
    uassertStatusOKWithContext(controlShardStatus, "unable to parse control shard");
    std::string controlShardName = controlShardStatus.getValue().getName();

    // Tick clusterTime to get a new topologyTime for this mutation of the topology.
    auto newTopologyTime = VectorClockMutable::get(opCtx)->tickClusterTime(1);

    // Use applyOps to both remove the shard's document and update topologyTime on another document.
    auto command =
        makeCommitRemoveShardCommand(name, controlShardName, newTopologyTime.asTimestamp());

    StatusWith<Shard::CommandResponse> applyOpsCommandResponse =
        configShard->runCommandWithFixedRetryAttempts(
            opCtx,
            ReadPreferenceSetting{ReadPreference::PrimaryOnly},
            ShardType::ConfigNS.db().toString(),
            command,
            Shard::RetryPolicy::kIdempotent);

    uassertStatusOKWithContext(applyOpsCommandResponse,
                               str::stream()
                                   << "error completing removeShard operation on: " << name);
    uassertStatusOKWithContext(applyOpsCommandResponse.getValue().commandStatus,
                               str::stream()
                                   << "error completing removeShard operation on: " << name);

    // The shard which was just removed must be reflected in the shard registry, before the replica
    // set monitor is removed, otherwise the shard would be referencing a dropped RSM.
    Grid::get(opCtx)->shardRegistry()->reload(opCtx);

    ReplicaSetMonitor::remove(name);

    // Record finish in changelog
    ShardingLogging::get(opCtx)->logChange(
        opCtx, "removeShard", "", BSON("shard" << name), ShardingCatalogClient::kLocalWriteConcern);

    return {RemoveShardProgress::COMPLETED,
            boost::optional<RemoveShardProgress::DrainingShardUsage>(boost::none)};
}

void ShardingCatalogManager::appendConnectionStats(executor::ConnectionPoolStats* stats) {
    _executorForAddShard->appendConnectionStats(stats);
}

StatusWith<long long> ShardingCatalogManager::_runCountCommandOnConfig(OperationContext* opCtx,
                                                                       const NamespaceString& nss,
                                                                       BSONObj query) {
    BSONObjBuilder countBuilder;
    countBuilder.append("count", nss.coll());
    countBuilder.append("query", query);

    auto configShard = Grid::get(opCtx)->shardRegistry()->getConfigShard();
    auto resultStatus =
        configShard->runCommandWithFixedRetryAttempts(opCtx,
                                                      kConfigReadSelector,
                                                      nss.db().toString(),
                                                      countBuilder.done(),
                                                      Shard::kDefaultConfigCommandTimeout,
                                                      Shard::RetryPolicy::kIdempotent);
    if (!resultStatus.isOK()) {
        return resultStatus.getStatus();
    }
    if (!resultStatus.getValue().commandStatus.isOK()) {
        return resultStatus.getValue().commandStatus;
    }

    auto responseObj = std::move(resultStatus.getValue().response);

    long long result;
    auto status = bsonExtractIntegerField(responseObj, "n", &result);
    if (!status.isOK()) {
        return status;
    }

    return result;
}

}  // namespace mongo