Briefly, this error occurs when Elasticsearch is trying to form a cluster using the specified discovery type and host providers, but it’s encountering issues. This could be due to incorrect configuration settings or network connectivity problems. To resolve this, ensure that the discovery settings in your Elasticsearch configuration file are correct. Also, check your network connectivity to ensure that all nodes can communicate with each other. If you’re using cloud-based host providers, ensure that the correct credentials and endpoints are provided.
Before you begin reading about how to correct this error, we recommend you run the Elasticsearch Error Check-Up which can help you resolve it and prevent future errors from occurring.
This guide will help you check for common problems that cause the log “using discovery type and host providers” to appear. It’s important to understand the issues related to it, so to get started, read the general overview on common issues and tips related to discovery in Elasticsearch.
Background
Discovery and cluster formation is affected by several settings. discovery.type is one such setting. This setting is used to specify if Elasticsearch should form a multi-node cluster or not. If you intend to run Elasticsearch on a single-node, then you need to specify this setting in elasticsearch.yml.
By default, Elasticsearch allows the nodes to join the cluster (if other nodes are discovered while forming the cluster), hence, forming a multi-node cluster.
How to reproduce this log
Add the below config in elasticsearch.yml.
http.port: 9200 discovery.type: single-node
Then start Elasticsearch from the command line as follows:
./bin/elasticsearch
The following logs are generated:
[INFO ][o.e.d.DiscoveryModule ] using discovery type [single-node] and seed hosts providers [settings] [INFO ][o.e.n.Node ] initialized
What this error means
This log message is an INFO message that a single-node Elasticsearch cluster has been started for development or testing. This is enabled by using discovery.type: single-node in elasticsearch.yml.
The seed host providers provide a list of the addresses of the master-eligible nodes in the cluster. Both these settings affect the cluster and discovery formation.
Based on your discovery type settings you will see the log lines.To know more about these settings, refer to this official documentation.
Overview
The process known as discovery occurs when an Elasticsearch node starts, restarts or loses contact with the master node for any reason. In those cases, the node needs to contact other nodes in the cluster to find any existing master node or initiate the election of a new master node.
How it works
Upon startup, each node looks for other nodes, firstly by contacting the IP addresses of eligible master nodes held in the previous cluster state. If they are not available, it will look for nodes based upon the seed host provider mechanisms available.
Seed host providers may be defined in 3 ways: list based, file based or plugin based. All of these methods provide a list of IP addresses or hostnames which the node should contact in order to obtain a list of master eligible nodes. The node will contact all of these addresses in turn, until either an active master is found, or failing that, until sufficient nodes can be found to elect a new master node.
Examples
The simplest form is to define a list of seed host providers in elasticsearch.yml:
discovery.seed_hosts: - 192.168.1.10:9300 - 192.168.1.11 - seeds.mydomain.com
An alternative way is to refer to a file using the following setting:
discovery.seed_providers: file
The file MUST be placed in the following filepath: $ES_PATH_CONF/unicast_hosts.txt
10.10.10.5 10.10.10.6:9305 10.10.10.5:10005 # an IPv6 address [2001:0db8:85a3:0000:0000:8a2e:0370:7334]:9301
Note that the use of a port is optional. If not used, then the default port range of 9300-9400 will be used.
If you use AWS or GCS then you can install and use a plugin to obtain a list of seed hosts from an API. A plugin also exists for Azure but is deprecated since version 5.
AWS plugin
A typical configuration could be as follows:
discovery.seed_providers: ec2 discovery.ec2.tag.role: master discovery.ec2.tag.environment: dev discovery.ec2.endpoint: ec2.us-east-1.amazonaws.com cloud.node.auto_attributes: true cluster.routing.allocation.awareness.attributes: aws_availability_zone
The above configuration would look for all nodes with a tag called “environment” set to “dev” and a tag called “role” set to “master”, in the AWS zone us-east-1. The last two lines set up cluster routing allocation awareness based upon aws availability zones. (Not necessary, but nice to have).
GCE plugin
A typical configuration could be as follows:
discovery.seed_providers: gce cloud.gce.project_id: <your-google-project-id> cloud.gce.zone: <your-zone> discovery.gce.tags: <my-tag-name>
The above configuration would look for all virtual machines inside your project, zone and with a tag set to the tag name you provide.
Notes and good things to know
Cluster formation depends on correct setup of the network.host settings in elasticsearch.yml. Make sure that the nodes can reach each other across the network using their IP addresses / hostname, and are not getting blocked due to firewall settings on the ports required.
Log Context
Log “using discovery type [{}] and host providers {}” classname is DiscoveryModule.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
String discoveryType = DISCOVERY_TYPE_SETTING.get(settings);
Supplier discoverySupplier = discoveryTypes.get(discoveryType);
if (discoverySupplier == null) {
throw new IllegalArgumentException("Unknown discovery type [" + discoveryType + "]");
}
logger.info("using discovery type [{}] and host providers {}"; discoveryType; hostsProviderNames);
discovery = Objects.requireNonNull(discoverySupplier.get());
}
public Discovery getDiscovery() {
return discovery;
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