Building a cluster¶
Every instance of Elasticsearch server is called a node. A collection of connected nodes is called a cluster. All nodes know about all the other nodes in the cluster and can forward client requests to the appropriate node.
Besides that, each node serves one or more purpose:
- Master-eligible node - A node that has node.master set to true (default), which makes it eligible to be elected as the master node, which controls the cluster
- Data node - A node that has node.data set to true (default). Data nodes hold data and perform data related operations such as CRUD, search, and aggregations
- Client node - A client node has both node.master and node.data set to false. It can neither hold data nor become the master node. It behaves as a “smart router” and is used to forward cluster-level requests to the master node and data-related requests (such as search) to the appropriate data nodes
- Tribe node - A tribe node, configured via the tribe.* settings, is a special type of client node that can connect to multiple clusters and perform search and other operations across all connected clusters.
Elasticsearch require little configuration before before going into work.
The following settings must be considered before going to production:
- path.data and path.logs - default locations of these files are:
- cluster.name - A node can only join a cluster when it shares its
cluster.namewith all the other nodes in the cluster. The default name is “elasticsearch”, but you should change it to an appropriate name which describes the purpose of the cluster. You can do this in
- node.name - By default, Elasticsearch will use the first seven characters of the randomly
generated UUID as the node id. Node id is persisted and does not change when a node restarts.
It is worth configuring a more human readable name:
node.name: prod-data-2in file
- network.host - parametr specifying network interfaces to which Elasticsearch can bind.
- discovery - Elasticsearch uses a custom discovery implementation called “Zen Discovery”.
There are two important settings:
discovery.zen.ping.unicast.hosts- specify list of other nodes in the cluster that are likely to be live and contactable;
discovery.zen.minimum_master_nodes- to prevent data loss, you can configure this setting so that each master-eligible node knows the minimum number of master-eligible nodes that must be visible in order to form a cluster.
- heap size - By default, Elasticsearch tells the JVM to use a heap with a minimum (Xms) and maximum (Xmx) size of 1 GB. When moving to production, it is important to configure heap size to ensure that Elasticsearch has enough heap available
To configure the Elasticsearch cluster you must specify some parameters in the following configuration files on every node that will be connected to the cluster:
cluster.name:name_of_the_cluster- same for every node;
node.name:name_of_the_node- uniq for every node;
logger: action: DEBUG- for easier debugging.
Example of the Elasticsearch cluster configuration:
cluster.name: tm-lab node.name: "elk01" node.master: true node.data: true network.host: 127.0.0.1,10.0.0.4 http.port: 9200 discovery.zen.ping.multicast.enabled: false discovery.zen.ping.unicast.hosts: ["10.0.0.4:9300","10.0.0.5:9300","10.0.0.6:9300"]
to start the Elasticsearch cluster execute command:
# systemctl restart elasticsearch
to check status of the Elstaicsearch cluster execute command:
check of the Elasticsearch cluster nodes status via tcp port:
# curl -XGET '127.0.0.1:9200/_cat/nodes?v' host ip heap.percent ram.percent load node.role master name 10.0.0.4 10.0.0.4 18 91 0.00 - - elk01 10.0.0.5 10.0.0.5 66 91 0.00 d * elk02 10.0.0.6 10.0.0.6 43 86 0.65 d m elk03 10.0.0.7 10.0.0.7 45 77 0.26 d m elk04
check status of the Elasticsearch cluster via log file:
# tail -f /var/log/elasticsearch/tm-lab.log (cluster.name)
Adding a new node to existing cluster¶
Install the new Energy instance. The description of the installation can be found in the chapter “First configuration steps”
Change the following parameters in the configuration file:
cluster.name:name_of_the_cluster same for every node;
node.name:name_of_the_node uniq for every node;
discovery.zen.ping.unicast.hosts:[“10.0.0.4:9300”,”10.0.0.5:9300”,”10.0.0.6:9300”] - IP addresses and instances of nodes in the cluster.
If you add a node with the role
data, delete the contents of the
path.data directory, by default in
Restart the Elasticsearch instance of the new node:
systemctl restart elasticsearch