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Description

MongoDB Error 70, 'Shard Not Found', indicates that a `mongos` query router cannot locate a required shard in the sharded cluster. This typically occurs when a shard is offline, has been improperly removed, or the cluster's configuration metadata is inconsistent.

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Error Message

Shard Not Found

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Known Causes

4 known causes

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Shard Node Unavailable

A `mongod` instance or an entire shard replica set is offline or unreachable by the `mongos` router.

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Inconsistent Cluster Metadata

The configuration servers hold incorrect or outdated information about the active shards in the cluster.

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Network Reachability Issues

`mongos` cannot establish a connection to the shard due to network partitions, firewall rules, or incorrect IP/port configurations.

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Improper Shard Removal

A shard was removed from the cluster without following proper de-sharding procedures, leaving its metadata inconsistent.

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Solutions

3 solutions available

1. Verify Shard Registration in Config Servers medium

Ensure the shard is correctly registered and visible to the config servers.

1

Connect to one of your MongoDB config servers using the `mongo` shell.

mongo --host <config_server_host>:<config_server_port>

2

Query the `config.shards` collection to list all registered shards.

db.shards.find().pretty()

3

Compare the output with your expected list of shards. If the shard reporting the error is missing or has an incorrect hostname/port, it needs to be re-added.

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4

If the shard is missing, add it back using the `sh.addShard()` command. Replace `<shard_name>` and `<shard_host>` with the actual values.

sh.addShard("<shard_name>@<shard_host>:<shard_port>")

5

If the shard is present but has incorrect details, you might need to remove and re-add it. First, remove the incorrect shard entry.

sh.removeShard("<shard_name>")

6

Then, add the shard back with the correct details.

sh.addShard("<shard_name>@<shard_host>:<shard_port>")

2. Check Shard Server Status easy

Confirm that the shard server itself is running and accessible.

1

Attempt to connect to the shard server directly using the `mongo` shell.

mongo --host <shard_host>:<shard_port>

2

If the connection fails, verify that the `mongod` process is running on the shard server.

sudo systemctl status mongod

3

If the `mongod` process is not running, start it.

sudo systemctl start mongod

4

Ensure that there are no firewall rules blocking access to the shard server's MongoDB port.

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3. Restart Sharding Services easy

A restart can resolve transient network or service issues affecting shard discovery.

1

Gracefully shut down the `mongod` process on the affected shard server.

sudo systemctl stop mongod

2

Wait for a short period (e.g., 30 seconds) to ensure all processes have terminated.

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3

Start the `mongod` process on the shard server again.

sudo systemctl start mongod

4

Monitor the MongoDB logs on both the shard server and the config servers for any new errors.

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Related Errors

5 related errors

MongoDB Error 70: Shard Not Found