Remote clusters
editRemote clusters
editThe remote clusters functionality enables you to establish unidirectional connections to a remote cluster. Remote clusters are required for cross-cluster replication and cross-cluster search.
Remote cluster connections work by configuring a remote cluster and connecting to a limited number of nodes in that remote cluster. There are two modes for remote cluster connections: sniff mode and proxy mode.
All the communication required between different clusters goes through the transport layer. Remote cluster connections consist of uni-directional connections from the coordinating node to the remote remote connections.
Sniff mode
editIn sniff mode, a cluster is created using a name and a list of seed nodes. When a remote cluster is registered, its cluster state is retrieved from one of the seed nodes and up to three gateway nodes are selected as part of remote cluster requests. This mode requires that the gateway node’s publish addresses are accessible by the local cluster.
Sniff mode is the default connection mode.
Gateway nodes selection
editThe gateway nodes selection depends on the following criteria:
- version: Remote nodes must be compatible with the cluster they are registered to. This is subject to rules that are similar to those for Rolling upgrades. Any node can communicate with any other node on the same major version (e.g. 7.0 can talk to any 7.x node). Only nodes on the last minor version of a certain major version can communicate with nodes on the following major version. Note that in the 6.x series, 6.8 can communicate with any 7.x node, while 6.7 can only communicate with 7.0. Version compatibility is symmetric, meaning that if 6.7 can communicate with 7.0, 7.0 can also communicate with 6.7. The matrix below summarizes compatibility as described above.
Compatibility |
5.0→5.5 |
5.6 |
6.0→6.6 |
6.7 |
6.8 |
7.0 |
7.1→7.x |
5.0→5.5 |
Yes |
Yes |
No |
No |
No |
No |
No |
5.6 |
Yes |
Yes |
Yes |
Yes |
Yes |
No |
No |
6.0→6.6 |
No |
Yes |
Yes |
Yes |
Yes |
No |
No |
6.7 |
No |
Yes |
Yes |
Yes |
Yes |
Yes |
No |
6.8 |
No |
Yes |
Yes |
Yes |
Yes |
Yes |
Yes |
7.0 |
No |
No |
No |
Yes |
Yes |
Yes |
Yes |
7.1→7.x |
No |
No |
No |
No |
Yes |
Yes |
Yes |
- role: Dedicated master nodes never get selected.
- attributes: You can tag which nodes should be selected (see Remote cluster settings for all modes), though such tagged nodes still have to satisfy the two above requirements.
Proxy mode
editIn proxy mode, a cluster is created using a name and a single proxy address. When a remote cluster is registered, a configurable number of socket connections are opened to the proxy address. The proxy is required to route those connections to the remote cluster. Proxy mode does not require remote cluster nodes to have accessible publish addresses.
The proxy mode is not the default connection mode and must be configured. Similar to the sniff gateway nodes, the remote connections are subject to the same version compatibility rules as Rolling upgrades.
Configuring remote clusters
editYou can configure remote clusters globally by using
cluster settings, which you can update dynamically.
Alternatively, you can configure them locally on individual nodes by using the
elasticsearch.yml
file.
If you specify the settings in elasticsearch.yml
files, only the nodes with
those settings can connect to the remote cluster. In other words, functionality
that relies on remote cluster requests must be driven specifically from those
nodes. For example:
cluster: remote: cluster_one: seeds: 127.0.0.1:9300 transport.ping_schedule: 30s cluster_two: mode: sniff seeds: 127.0.0.1:9301 transport.compress: true skip_unavailable: true cluster_three: mode: proxy proxy_address: 127.0.0.1:9302
|
|
The hostname and transport port (default: 9300) of a seed node in the remote cluster. |
|
A keep-alive ping is configured for |
|
The configured connection mode. By default, this is |
|
Compression is explicitly enabled for requests to |
|
Disconnected remote clusters are optional for |
|
The address for the proxy endpoint used to connect to |
For more information about the optional transport settings, see Transport.
If you use cluster settings, the remote clusters are available on every node in the cluster. For example:
PUT _cluster/settings { "persistent": { "cluster": { "remote": { "cluster_one": { "seeds": [ "127.0.0.1:9300" ], "transport.ping_schedule": "30s" }, "cluster_two": { "mode": "sniff", "seeds": [ "127.0.0.1:9301" ], "transport.compress": true, "skip_unavailable": true }, "cluster_three": { "mode": "proxy", "proxy_address": "127.0.0.1:9302" } } } } }
You can dynamically update the compression and ping schedule settings. However,
you must re-include seeds or proxy_address
in the settings update request.
For example:
PUT _cluster/settings { "persistent": { "cluster": { "remote": { "cluster_one": { "seeds": [ "127.0.0.1:9300" ], "transport.ping_schedule": "60s" }, "cluster_two": { "mode": "sniff", "seeds": [ "127.0.0.1:9301" ], "transport.compress": false }, "cluster_three": { "mode": "proxy", "proxy_address": "127.0.0.1:9302", "transport.compress": true } } } } }
When the compression or ping schedule settings change, all the existing node connections must close and re-open, which can cause in-flight requests to fail.
A remote cluster can be deleted from the cluster settings by setting its settings to null
:
PUT _cluster/settings { "persistent": { "cluster": { "remote": { "cluster_two": { "mode": null, "seeds": null, "skip_unavailable": null, "transport": { "compress": null } } } } } }
|
Remote cluster settings for all modes
editThese settings apply to both sniff mode and proxy mode. Sniff mode settings and proxy mode settings are described below.
-
cluster.remote.<cluster_alias>.mode
-
The mode used for a remote cluster connection. The only supported modes are
sniff
andproxy
. -
cluster.remote.initial_connect_timeout
-
The time to wait for remote connections to be established when the node
starts. The default is
30s
. -
node.remote_cluster_client
-
By default, any node in the cluster can act as a cross-cluster client and
connect to remote clusters. The
node.remote_cluster_client
setting can be set tofalse
(defaults totrue
) to prevent certain nodes from connecting to remote clusters. Remote cluster requests must be sent to a node that is allowed to act as a cross-cluster client. -
cluster.remote.<cluster_alias>.skip_unavailable
-
Per cluster boolean setting that allows to skip specific clusters when no
nodes belonging to them are available and they are the target of a remote
cluster request. Default is
false
, meaning that all clusters are mandatory by default, but they can selectively be made optional by setting this setting totrue
. -
cluster.remote.<cluster_alias>.transport.ping_schedule
-
Sets the time interval between regular application-level ping messages that
are sent to ensure that transport connections to nodes belonging to remote
clusters are kept alive. If set to
-1
, application-level ping messages to this remote cluster are not sent. If unset, application-level ping messages are sent according to the globaltransport.ping_schedule
setting, which defaults to-1
meaning that pings are not sent. -
cluster.remote.<cluster_alias>.transport.compress
-
Per cluster boolean setting that enables you to configure compression for
requests to a specific remote cluster. This setting impacts only requests
sent to the remote cluster. If the inbound request is compressed,
Elasticsearch compresses the response. If unset, the global
transport.compress
is used as the fallback setting.
Remote cluster settings for sniff mode
edit-
cluster.remote.<cluster_alias>.seeds
- The list of seed nodes used to sniff the remote cluster state.
-
cluster.remote.<cluster_alias>.node_connections
-
The number of gateway nodes to connect to for this remote cluster. The default
is
3
. -
cluster.remote.node.attr
-
A node attribute to filter out nodes that are eligible as a gateway node in
the remote cluster. For instance a node can have a node attribute
node.attr.gateway: true
such that only nodes with this attribute will be connected to ifcluster.remote.node.attr
is set togateway
.
Remote cluster settings for proxy mode
edit-
cluster.remote.<cluster_alias>.proxy_address
- The address used for all remote connections.
-
cluster.remote.<cluster_alias>.proxy_socket_connections
-
The number of socket connections to open per remote cluster. The default is
18
.
-
cluster.remote.<cluster_alias>.server_name
-
An optional hostname string which is sent in the
server_name
field of the TLS Server Name Indication extension if TLS is enabled. The TLS transport will fail to open remote connections if this field is not a valid hostname as defined by the TLS SNI specification.
Retrieving remote clusters info
editYou can use the remote cluster info API to retrieve information about the configured remote clusters, as well as the remote nodes that the node is connected to.