Introduction
Elasticsearch is a platform for distributed search and analysis of data in real-time. Its popularity is due to its ease of use, powerful features, and scalability.
Elasticsearch supports RESTful operations. This means that you can use HTTP methods (GET, POST, PUT, DELETE, etc.) in combination with an HTTP URI (/collection/entry) to manipulate your data. The intuitive RESTful approach is both developer and user-friendly, which is one of the reasons for Elasticsearch’s popularity.
Elasticsearch is free and open-source software with a solid company behind it — Elastic. This combination makes it suitable for use anywhere from personal testing to corporate integration.
This article will introduce you to Elasticsearch and show you how to install, configure, and start using it.
Prerequisites
Before following this tutorial, please make sure you complete the following prerequisites:
-
A CentOS 7 Droplet
A non-root sudo user (Check out Initial Server Setup with CentOS 7 for details.)
Except otherwise noted, all of the commands that require root privileges in this tutorial should be run as a non-root user with sudo privileges.
Assumptions
This tutorial assumes that your servers are using a VPN like the one described here: How To Use Ansible and Tinc VPN to Secure Your Server Infrastructure. This will provide private network functionality regardless of the physical network that your servers are using.
If you are using a shared private network, such as DigitalOcean Private Networking, you must use a VPN to protect Elasticsearch from unauthorized access. Each server must be on the same private network because Elasticsearch doesn’t have security built into its HTTP interface. The private network must not be shared with any computers you don’t trust.
Step 1 — Installing Java
First, you will need a Java Runtime Environment (JRE) on your Droplet because Elasticsearch is written in the Java programming language. You can use the native CentOS OpenJDK package for the JRE. This JRE is free, well-supported, and automatically managed through the CentOS Yum installation manager.
You can install the latest OpenJDK with the command:
sudo yum install java-1.8.0-openjdk.x86_64
To verify your JRE is installed and can be used, run the command:
java -version
The result should look like this:
Output of java -version openjdk version "1.8.0_65" OpenJDK Runtime Environment (build 1.8.0_65-b17) OpenJDK 64-Bit Server VM (build 25.65-b01, mixed mode)
When you advance in using Elasticsearch and you start looking for better Java performance and compatibility, you may opt to install Oracle’s proprietary Java (Oracle JDK 8). For more information on how to do this, please check the article on How To Install Java on CentOS and Fedora.
Step 2 — Downloading and Installing Elasticsearch
Elasticsearch can be downloaded directly from elastic.co in zip, tar.gz, deb, or rpm packages. For CentOS, it’s best to use the native rpm package which will install everything you need to run Elasticsearch.
At the time of this writing, the latest Elasticsearch version is 1.7.3. Download it in a directory of your choosing with the command:
wget https://download.elastic.co/elasticsearch/elasticsearch/elasticsearch-1.7.3.noarch.rpm
Then install it in the usual CentOS way with the rpm command like this:
sudo rpm -ivh elasticsearch-1.7.3.noarch.rpm
This results in Elasticsearch being installed in /usr/share/elasticsearch/ with its configuration files placed in /etc/elasticsearch and its init script added in /etc/init.d/elasticsearch.
To make sure Elasticsearch starts and stops automatically with the Droplet, add its init script to the default runlevels with the command:
sudo systemctl enable elasticsearch.service
Step 3 — Configuring Elastic
Now that Elasticsearch and its Java dependencies have been installed, it is time to configure Elasticsearch.
The Elasticsearch configuration files are in the /etc/elasticsearch directory. There are two files:
elasticsearch.yml — Configures the Elasticsearch server settings. This is where all options, except those for logging, are stored, which is why we are mostly interested in this file.
logging.yml — Provides configuration for logging. In the beginning, you don’t have to edit this file. You can leave all default logging options. You can find the resulting logs in /var/log/elasticsearch by default.
The first variables to customize on any Elasticsearch server are node.name and cluster.name in elasticsearch.yml. As their names suggest, node.name specifies the name of the server (node) and the cluster to which the latter is associated.
If you don’t customize these variables, a node.name will be assigned automatically in respect to the Droplet hostname. The cluster.name will be automatically set to the name of the default cluster.
The cluster.name value is used by the auto-discovery feature of Elasticsearch to automatically discover and associate Elasticsearch nodes to a cluster. Thus, if you don’t change the default value, you might have unwanted nodes, found on the same network, in your cluster.
To start editing the main elasticsearch.yml configuration file:
sudo nano /etc/elasticsearch/elasticsearch.yml
Remove the # character at the beginning of the lines for node.name and cluster.name to uncomment them, and then change their values. Your first configuration changes in the /etc/elasticsearch/elasticsearch.yml file should look like this:
/etc/elasticsearch/elasticsearch.yml
... node.name: "My First Node" cluster.name: mycluster1 ...
Another important setting is the role of the server, which could be either “master” or “slave”. “Masters” are responsible for the cluster's health and stability. In large deployments with a lot of cluster nodes, it’s recommended to have more than one dedicated “master.” Typically, a dedicated “master” will not store data or create indexes. Thus, there should be no chance of being overloaded, by which the cluster health could be endangered.
“Slaves” are used as “workhorses” which can be loaded with data tasks. Even if a “slave” node is overloaded, the cluster health shouldn’t be affected seriously, provided there are other nodes to take additional load.
The setting which determines the role of the server is called node.master. If you have only one Elasticsearch node, you should leave this option commented out so that it keeps its default value of true — i.e. the sole node should be also a master. Alternatively, if you wish to configure the node as a slave, remove the # character at the beginning of the node.master line, and change the value to false:
/etc/elasticsearch/elasticsearch.yml
... node.master: false ...
Another important configuration option is node.data, which determines whether a node will store data or not. In most cases, this option should be left to its default value (true), but there are two cases in which you might wish not to store data on a node. One is when the node is a dedicated “master,” as we have already mentioned. The other is when a node is used only for fetching data from nodes and aggregating results. In the latter case, the node will act up as a “search load balancer”.
Again, if you have only one Elasticsearch node, you should leave this setting commented out so that it keeps the default true value. Otherwise, to disable storing data locally, uncomment the following line and change the value to false:
/etc/elasticsearch/elasticsearch.yml
... node.data: false ...
Two other important options are index.number_of_shards and index.number_of_replicas. The first determines into how many pieces (shards) the index will be split into. The second defines the number of replicas that will be distributed across the cluster. Having more shards improves the indexing performance while having more replicas makes searching faster.
Assuming that you are still exploring and testing Elasticsearch on a single node, it’s better to start with only one shard and no replicas. Thus, their values should be set to the following (make sure to remove the # at the beginning of the lines):
/etc/elasticsearch/elasticsearch.yml
... index.number_of_shards: 1 index.number_of_replicas: 0 ...
One final setting which you might be interested in changing is path.data, which determines the path where data is stored. The default path is /var/lib/elasticsearch. In a production environment, it’s recommended that you use a dedicated partition and mount point for storing Elasticsearch data. In the best case, this dedicated partition will be a separate storage media which will provide better performance and data isolation. You can specify a different path.data path by uncommenting the path.data line and changing its value:
/etc/elasticsearch/elasticsearch.yml
... path.data: /media/different_media ...
Once you make all the changes, please save and exit the file. Now you can start Elasticsearch for the first time with the command:
sudo service elasticsearch start
Please allow at least 10 seconds for Elasticsearch to fully start before you are able to use it. Otherwise, you may get errors about not being able to connect.
Step 4 — Securing Elastic
Elasticsearch has no built-in security and can be controlled by anyone who can access the HTTP API. This section is not a comprehensive guide to securing Elasticsearch. Take whatever measures are necessary to prevent unauthorized access to it and the server/virtual machine on which it is running. Consider using iptables to further secure your system.
The first security tweak is to prevent public access. To remove public access edit the file elasticsearch.yml:
sudo nano /etc/elasticsearch/elasticsearch.yml
Find the line that contains the network.bind_host, uncomment it by removing the # character at the beginning of the line, and changing the value to localhost so it looks like this:
/etc/elasticsearch/elasticsearch.yml
... network.bind_host: localhost ...
Warning: Because Elasticsearch doesn’t have any built-in security, it is very important that you do not set this to any IP address that is accessible to any servers that you do not control or trust. Do not bind Elasticsearch to a public or shared private network IP address!
Also, for additional security, you can disable dynamic scripts which are used to evaluate custom expressions. By crafting a custom malicious expression, an attacker might be able to compromise your environment.
To disable custom expressions, add the following line is at the end of the /etc/elasticsearch/elasticsearch.yml file:
/etc/elasticsearch/elasticsearch.yml
... script.disable_dynamic: true ...
For the above changes to take effect, you will have to restart Elasticsearch with the command:
sudo service elasticsearch restart
Step 5 — Testing
By now, Elasticsearch should be running on port 9200. You can test it with curl, the command line client-side URL transfers tool, and a simple GET request like this:
curl -X GET 'http://localhost:9200'
You should see the following response:
Output of curl
{
"status" : 200,
"name" : "CentOS Node",
"cluster_name" : "mysqluster",
"version" : {
"number" : "1.7.3",
"build_hash" : "05d4530971ef0ea46d0f4fa6ee64dbc8df659682",
"build_timestamp" : "2015-10-15T09:14:17Z",
"build_snapshot" : false,
"lucene_version" : "4.10.4"
},
"tagline" : "You Know, for Search"
}
If you see a response similar to the one above, Elasticsearch is working properly. If not, make sure that you have followed correctly the installation instructions and you have allowed some time for Elasticsearch to fully start.
Step 6 — Using Elasticsearch
To start using Elasticsearch, let’s add some data first. As already mentioned, Elasticsearch uses a RESTful API, which responds to the usual CRUD commands: Create, Read, Update, and Delete. For working with it, we’ll use again curl.
You can add your first entry with the command:
curl -X POST 'http://localhost:9200/tutorial/helloworld/1' -d '{ "message": "Hello World!" }'
You should see the following response:
Output
{"_index":"tutorial","_type":"helloworld","_id":"1","_version":1,"created":true}
With curl, we have sent an HTTP POST request to the Elasticseach server. The URI of the request was /tutorial/helloworld/1. It’s important to understand the parameters here:
the tutorial is the index of the data in Elasticsearch.
helloworld is the type.
1 is the id of our entry under the above index and type.
You can retrieve this first entry with an HTTP GET request like this:
curl -X GET 'http://localhost:9200/tutorial/helloworld/1'
The result should look like:
Output
{"_index":"tutorial","_type":"helloworld","_id":"1","_version":1,"found":true,"_source":{ "message": "Hello World!" }}
To modify an existing entry you can use an HTTP PUT request like this:
curl -X PUT 'localhost:9200/tutorial/helloworld/1?pretty' -d '
{
"message": "Hello People!"
}'
Elasticsearch should acknowledge successful modification like this:
Output
{
"_index" : "tutorial",
"_type" : "helloworld",
"_id" : "1",
"_version" : 2,
"created" : false
}
In the above example, we have modified the message of the first entry to “Hello People!”. With that, the version number has been automatically increased to 2.
You may have noticed the extra argument pretty in the above request. It enables a human-readable format so that you can write each data field on a new row. You can also “prettify” your results when retrieving data and get much nicer output like this:
curl -X GET 'http://localhost:9200/tutorial/helloworld/1?pretty'
Now the response will be in a much better format:
Output
{
"_index" : "tutorial",
"_type" : "helloworld",
"_id" : "1",
"_version" : 2,
"found" : true,
"_source":{ "message": "Hello World!" }
}
Setup web server to host ElasticSearch Application
These options depend on the webservers you have currently installed
For example, if you have installed nginx/varnish/apache you can use:
i. nginx -> custom port - This will proxy directly to ElasticSearch Application(RECOMMENDED)
ii. nginx/varnish/apache -> custom port - This will proxy to varnish cache and then to apache and then to ElasticSearch Application
So far we have added to and queried data in Elasticsearch. To learn about the other operations please check the API documentation.
Conclusion
That’s how easy it is to install, configure, and begin using Elasticsearch. Once you have played enough with manual queries, your next task will be to start using it from your applications.