全文搜索属于最常见的需求，开源的 Elasticsearch是目前全文搜索引擎的首选。它可以快速地储存、搜索和分析海量数据。维基百科、Stack Overflow、Github 都采用它。Elasticsearch 的底层是开源库 Lucene。但你没法直接用 Lucene，必须自己写代码去调用它的接口。Elasticsearch是 Lucene 的封装，提供了 REST API 的操作接口，开箱即用。本文从零开始，讲解如何使用 Elasticsearch 搭建自己的全文搜索引擎。
安装JDK 8
Elasticsearch官方建议使用 Oracle的JDK8，在安装之前首先要确定下机器有没有安装JDK。
rpm -qa | grep -E '^open[jre|jdk]|j[re|dk]'
如果有，有可能是系统自带的openjdk，而非oracle的jdk。可以使用 rpm -qa | grep Java | xargs rpm -e --nodeps 批量卸载所有带有Java的文件，然后进行重新安装。
命令行下载 JDK 有个麻烦的地方，必须先要接受 Oracle 的许可协议，不过可以通过设置 cookie 来解决。
wget --no-check-certificate --no-cookies --header "Cookie: oraclelicense=accept-securebackup-cookie" http://download.oracle.com/otn-pub/java/jdk/8u101-b13/jdk-8u101-linux-x64.tar.gz
直接解压 tar -zxvf jdk-8u101-linux-x64.tar.gz 后。配置环境变量：
vi /etc/profile
添加如下内容，并保存：
# set java environment
export JAVA_HOME=/usr/local/jdk1.8.0_101
export JRE_HOME=${JAVA_HOME}/jre
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib
export PATH=${JAVA_HOME}/bin:${PATH}
保存后运行 source /etc/profile 使环境变量生效
输入java -version 确认是否安装成功。
[root@localhost local]# java -version java version "1.8.0_101" Java(TM) SE Runtime Environment (build 1.8.0_101-b13) Java HotSpot(TM) 64-Bit Server VM (build 25.101-b13, mixed mode)
安装 Elasticsearch
手动安装
最简单的方式是通过Yum或rpm的方式进行安装，这里介绍的是手动安装的方法：
1、进入官网查看最新版本的下载链接
2、使用命令行进行下载并解压：
wget https://download.elastic.co/elasticsearch/release/org/elasticsearch/distribution/tar/elasticsearch/2.4.0/elasticsearch-2.4.0.tar.gz tar -zxvf elasticsearch-2.4.0.tar.gz
3、运行Elasticsearch
执行 sh /usr/local/elasticsearch-2.4.0/bin/elasticsearch -d 其中-d表示后台启动
不出意外，可以看到如下报错信息：
[root@localhost bin]# Exception in thread "main" java.lang.RuntimeException: don't run elasticsearch as root.
at org.elasticsearch.bootstrap.Bootstrap.initializeNatives(Bootstrap.java:94)
at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:160)
at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:286)
at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:35)
Refer to the log for complete error details.
原因是elasticsearch 默认是不支持用root用户来启动的。
解决方案一：Des.insecure.allow.root=true
修改/usr/local/elasticsearch-2.4.0/bin/elasticsearch，添加ES_JAVA_OPTS=”-Des.insecure.allow.root=true”
或执行时添加：sh /usr/local/elasticsearch-2.4.0/bin/elasticsearch -d -Des.insecure.allow.root=true
注意：正式环境用root运行可能会有安全风险，不建议用root来跑。
解决方案二：添加专门的用户
useradd elastic chown -R elastic:elastic elasticsearch-2.4.0 su elastic sh /usr/local/elasticsearch-2.4.0/bin/elasticsearch -d
使用 curl http://localhost:9200/ 查看是否运行，如果返回如下信息则标示运行正常：
[elastic@localhost local]$ curl http://localhost:9200/
{
"name" : "Astrid Bloom",
"cluster_name" : "elasticsearch",
"version" : {
"number" : "2.4.0",
"build_hash" : "ce9f0c7394dee074091dd1bc4e9469251181fc55",
"build_timestamp" : "2016-08-29T09:14:17Z",
"build_snapshot" : false,
"lucene_version" : "5.5.2"
},
"tagline" : "You Know, for Search"
}
Elasticsearch默认restful-api的端口是9200 不支持Ip地址，只能在本机用http://localhost:9200来访问。如果需要改变，需要修改配置文件。
默认情况下 Elasticsearch 的 RESTful 服务只有本机才能访问，也就是说无法从主机访问虚拟机中的服务。为了方便调试，可以修改 /etc/elasticsearch/config/elasticsearch.yml 文件，加入以下两行：
network.bind_host: “0.0.0.0" network.publish_host: _nonloopback:ipv4
或去除network.host 和http.port之前的注释，并将network.host的IP地址修改为本机外网IP。然后重启，Elasticsearch 关闭方法（输入命令：ps -ef | grep elasticsearch ，找到进程，然后kill掉就行了。
如果外网还是不能访问，则有可能是防火墙设置导致的。
使用YUM安装
添加elasticsearch的repo，在/etc/yum.repos.d/下新增elasticsearch.repo：
vi /etc/yum.repos.d/elasticsearch.repo
文件内容如下：
[elasticsearch-5.x] name=Elasticsearch repository for 5.x packages baseurl=https://artifacts.elastic.co/packages/5.x/yum gpgcheck=1 gpgkey=https://artifacts.elastic.co/GPG-KEY-elasticsearch enabled=1 autorefresh=1 type=rpm-md
然后使用最简单的yum命令即可进行安装：
yum install elasticsearch
使用RPM安装
wget https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-5.1.1.rpm rpm --install elasticsearch-5.1.1.rpm
也是非常的简单。
防火墙设置
关闭selinux
sed -i "s/SELINUX=enforcing/SELINUX=disabled/" /etc/selinux/config setenforce 0
安装firewall
yum install firewalld firewall-config systemctl start firewalld.service systemctl enable firewalld.service systemctl status firewalld.service
开放端口
firewall-cmd --permanent --add-port={9200/tcp,9300/tcp}
firewall-cmd --reload
firewall-cmd --state
firewall-cmd --list-all
至此，elasticsearch就顺利安装完成了，但是为了更好的使用，还需要安装中文分析工具等插件，下篇文章再做介绍。
使用systemd管理elasticsearch服务
/bin/systemctl daemon-reload #重启加载systemd /bin/systemctl enable elasticsearch.service #自启动elasticsearch systemctl start elasticsearch.service #启动elasticsearch systemctl stop elasticsearch.service #停止elasticsearch
Elsticsearch配置说明
如果使用yum或rpm方式安装Elasticsearch默认的配置文件地址是：/etc/elasticsearch/elasticsearch.yml，详细的配置说明可以参考Configuring Elasticsearch。另外还有一个系统配置存放在/etc/sysconfig/elasticsearch，可设置的内容包含如下参数：
| ES_USER | The user to run as, defaults to elasticsearch. |
| ES_GROUP | The group to run as, defaults to elasticsearch. |
| JAVA_HOME | Set a custom Java path to be used. |
| MAX_OPEN_FILES | Maximum number of open files, defaults to 65536. |
| MAX_LOCKED_MEMORY | Maximum locked memory size. Set to unlimited if you use thebootstrap.memory_lock option in elasticsearch.yml. |
| MAX_MAP_COUNT | Maximum number of memory map areas a process may have. If you use mmapfsas index store type, make sure this is set to a high value. For more information, check the linux kernel documentation about max_map_count. This is set via sysctl before starting elasticsearch. Defaults to 262144. |
| LOG_DIR | Log directory, defaults to /var/log/elasticsearch. |
| DATA_DIR | Data directory, defaults to /var/lib/elasticsearch. |
| CONF_DIR | Configuration file directory (which needs to include elasticsearch.ymland log4j2.properties files), defaults to /etc/elasticsearch. |
| ES_JAVA_OPTS | Any additional JVM system properties you may want to apply. |
| RESTART_ON_UPGRADE | Configure restart on package upgrade, defaults to false. This means you will have to restart your elasticsearch instance after installing a package manually. The reason for this is to ensure, that upgrades in a cluster do not result in a continuous shard reallocation resulting in high network traffic and reducing the response times of your cluster. |
另外，一些默认安装的文件路径如下：
| Type | Description | Default Location | Setting |
| home | Elasticsearch home directory or $ES_HOME | /usr/share/elasticsearch | |
| bin | Binary scripts including elasticsearch to start a node and elasticsearch-plugin to install plugins | /usr/share/elasticsearch/bin | |
| conf | Configuration files including elasticsearch.yml | /etc/elasticsearch | path.conf |
| conf | Environment variables including heap size, file descriptors. | /etc/sysconfig/elasticsearch | |
| data | The location of the data files of each index / shard allocated on the node. Can hold multiple locations. | /var/lib/elasticsearch | path.data |
| logs | Log files location. | /var/log/elasticsearch | path.logs |
| plugins | Plugin files location. Each plugin will be contained in a subdirectory. | /usr/share/elasticsearch/plugins | |
| repo | Shared file system repository locations. Can hold multiple locations. A file system repository can be placed in to any subdirectory of any directory specified here. | Not configured | path.repo |
| script | Location of script files. | /etc/elasticsearch/scripts | path.scripts |
参考链接：
