# CLUSTER MEET

```json metadata
{
  "schema_version": 2,
  "title": "CLUSTER MEET",
  "description": "Forces a node to handshake with another node.",
  "categories": ["docs","develop","stack","oss","rs","rc","oss","kubernetes","clients"],
  "arguments": [{"display_text":"ip","name":"ip","type":"string"},{"display_text":"port","name":"port","type":"integer"},{"display_text":"cluster-bus-port","name":"cluster-bus-port","optional":true,"since":"4.0.0","type":"integer"}],
  "syntax_fmt": "CLUSTER MEET ip port [cluster-bus-port]",
  "complexity": "O(1)",
  "group": "cluster",
  "command_flags": ["admin","stale","no_async_loading"],
  "acl_categories": ["@admin","@slow","@dangerous"],
  "since": "3.0.0",
  "arity": -4,
  "tableOfContents": {"sections":[{"id":"required-arguments","title":"Required arguments"},{"id":"optional-arguments","title":"Optional arguments"},{"children":[{"id":"implementation-meet-and-ping-packets","title":"Implementation: MEET and PING packets"}],"id":"details","title":"Details"},{"id":"redis-software-and-redis-cloud-compatibility","title":"Redis Software and Redis Cloud compatibility"},{"id":"return-information","title":"Return information"}]}

,
  "codeExamples": []
}
```

`CLUSTER MEET` is used in order to connect different Redis nodes with cluster
support enabled, into a working cluster.

The basic idea is that nodes by default don't trust each other, and are
considered unknown, so that it is unlikely that different cluster nodes will
mix into a single one because of system administration errors or network
addresses modifications.

So in order for a given node to accept another one into the list of nodes
composing a Redis Cluster, there are only two ways:

1. The system administrator sends a `CLUSTER MEET` command to force a node to meet another one.
2. An already known node sends a list of nodes in the gossip section that we are not aware of. If the receiving node trusts the sending node as a known node, it will process the gossip section and send a handshake to the nodes that are still not known.

Note that Redis Cluster needs to form a full mesh (each node is connected with each other node), but in order to create a cluster, there is no need to send all the `CLUSTER MEET` commands needed to form the full mesh. What matter is to send enough `CLUSTER MEET` messages so that each node can reach each other node through a *chain of known nodes*. Thanks to the exchange of gossip information in heartbeat packets, the missing links will be created.

So, if we link node A with node B via `CLUSTER MEET`, and B with C, A and C will find their ways to handshake and create a link.

Another example: if we imagine a cluster formed of the following four nodes called A, B, C and D, we may send just the following set of commands to A:

1. `CLUSTER MEET B-ip B-port`
2. `CLUSTER MEET C-ip C-port`
3. `CLUSTER MEET D-ip D-port`

As a side effect of `A` knowing and being known by all the other nodes, it will send gossip sections in the heartbeat packets that will allow each other node to create a link with each other one, forming a full mesh in a matter of seconds, even if the cluster is large.

Moreover `CLUSTER MEET` does not need to be reciprocal. If I send the command to A in order to join B, I don't need to also send it to B in order to join A.

If the optional `cluster_bus_port` argument is not provided, the default of client port number + 10,000 will be used.

## Required arguments

<details open><summary><code>ip</code></summary>

The IP address of the node to add to the cluster.

</details>

<details open><summary><code>port</code></summary>

The client port of the node to add.

</details>

## Optional arguments

<details open><summary><code>cluster-bus-port</code></summary>

The cluster bus port of the node. If omitted, it defaults to the client port number plus 10,000.

</details>

## Details

### Implementation: MEET and PING packets

When you send CLUSTER MEET to a node, the node specified in the command does not yet know the receiving node. To establish trust, the receiving node sends a MEET packet to the specified node instead of a [PING](https://redis.io/docs/latest/commands/ping) packet. The two packets have the same format, but MEET forces the specified node to trust the sender.

## Redis Software and Redis Cloud compatibility

| Redis<br />Software | Redis<br />Cloud | <span style="min-width: 9em; display: table-cell">Notes</span> |
|:----------------------|:-----------------|:------|
| <span title="Not supported">&#x274c; Standard</span><br /><span title="Not supported"><nobr>&#x274c; Active-Active</nobr></span> | <span title="Not supported">&#x274c; Standard</span><br /><span title="Not supported"><nobr>&#x274c; Active-Active</nobr></span> |  |

## Return information

**RESP2:**

[Simple string reply](../../develop/reference/protocol-spec#simple-strings): `OK` if the command was successful. If the address or port specified are invalid an error is returned.

**RESP3:**

[Simple string reply](../../develop/reference/protocol-spec#simple-strings): `OK` if the command was successful. If the address or port specified are invalid an error is returned.