convert-sharded-cluster-to-replica-set.txt

======================================
Convert Sharded Cluster to Replica Set
======================================

.. default-domain:: mongodb

.. contents:: On this page
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   :class: singlecol

This tutorial describes the process for converting a :term:`sharded
cluster` to a non-sharded :term:`replica set`. To convert a replica
set into a sharded cluster
:doc:`/tutorial/convert-replica-set-to-replicated-shard-cluster`. See the
:doc:`/sharding` documentation for more information on sharded
clusters.

Convert a Cluster with a Single Shard into a Replica Set
--------------------------------------------------------

In the case of a :term:`sharded cluster` with only one shard, that shard
contains the full data set. Use the following procedure to convert that
cluster into a non-sharded :term:`replica set`:

1. Reconfigure the application to connect to the primary member of the
   replica set hosting the single shard that system will be the new replica
   set.

#. Optionally remove the :option:`--shardsvr <mongod --shardsvr>`
   option, if your :binary:`~bin.mongod` started with this option.

   .. tip:: Changing the :option:`--shardsvr <mongod --shardsvr>`
      option will change the port that :binary:`~bin.mongod` listens for
      incoming connections on.

The single-shard cluster is now a non-sharded :term:`replica set` that
will accept read and write operations on the data set.

You may now decommission the remaining sharding infrastructure.

Convert a Sharded Cluster into a Replica Set
--------------------------------------------

Use the following procedure to transition from a :term:`sharded cluster`
with more than one shard to an entirely new :term:`replica set`.

1. With the :term:`sharded cluster` running, :doc:`deploy a new replica
   set <deploy-replica-set>` in addition to your sharded cluster. The
   replica set must have sufficient capacity to hold all of the data
   files from all of the current shards combined. Do not configure the
   application to connect to the new replica set until the data
   transfer is complete.

#. Stop all writes to the :term:`sharded cluster`. You may reconfigure
   your application or stop all :binary:`~bin.mongos` instances. If you
   stop all :binary:`~bin.mongos` instances, the applications will not be
   able to read from the database. If you stop all :binary:`~bin.mongos`
   instances, start a temporary :binary:`~bin.mongos` instance on that
   applications cannot access for the data migration procedure.

#. Use :doc:`mongodump and mongorestore
   </tutorial/backup-with-mongodump/>` to migrate
   the data from the :binary:`~bin.mongos` instance to the new
   :term:`replica set`.

   .. note:: Not all collections on all databases are necessarily
      sharded. Do not solely migrate the sharded collections. Ensure that
      all databases and all collections migrate correctly.

#. Reconfigure the application to use the non-sharded :term:`replica
   set` instead of the :binary:`~bin.mongos` instance.

The application will now use the un-sharded :term:`replica set` for
reads and writes. You may now decommission the remaining unused
sharded cluster infrastructure.