背景
旧版本ElasticSearch为6.4.0，升级到官网最新版本7.3.1。
升级步骤
ElasticSearch官网下载最新7.3.1版本，下载地址https://www.elastic.co/cn/downloads/elasticsearch；
解压tar.gz文件，进入config目录，设置elasticsearch.yml文件，具体设置如下：
# ======================== Elasticsearch Configuration =========================
#
# NOTE: Elasticsearch comes with reasonable defaults for most settings.
# Before you set out to tweak and tune the configuration, make sure you
# understand what are you trying to accomplish and the consequences.
#
# The primary way of configuring a node is via this file. This template lists
# the most important settings you may want to configure for a production cluster.
#
# Please consult the documentation for further information on configuration options:
# https://www.elastic.co/guide/en/elasticsearch/reference/index.html
#
# ---------------------------------- Cluster -----------------------------------
#
# Use a descriptive name for your cluster:
#
cluster.name: zhangfang
#
# ------------------------------------ Node ------------------------------------
#
# Use a descriptive name for the node:
#
node.name: node-3
#
# Add custom attributes to the node:
#
#node.attr.rack: r1
#
# ----------------------------------- Paths ------------------------------------
#
# Path to directory where to store the data (separate multiple locations by comma):
#
path.data: /data/lib/elastic
#
# Path to log files:
#
path.logs: /data/log/elastic
#
# ----------------------------------- Memory -----------------------------------
#
# Lock the memory on startup:
#
bootstrap.memory_lock: false
bootstrap.system_call_filter: false
#
# Make sure that the heap size is set to about half the memory available
# on the system and that the owner of the process is allowed to use this
# limit.
#
# Elasticsearch performs poorly when the system is swapping the memory.
#
# ---------------------------------- Network -----------------------------------
#
# Set the bind address to a specific IP (IPv4 or IPv6):
#
network.host: 172.28.25.52
#
# Set a custom port for HTTP:
#
http.port: 9200
transport.tcp.port: 9300
#
# For more information, consult the network module documentation.
#
# --------------------------------- Discovery ----------------------------------
#
# Pass an initial list of hosts to perform discovery when new node is started:
# The default list of hosts is ["127.0.0.1", "[::1]"]
#
discovery.zen.ping.unicast.hosts: ["172.28.25.54:9300", "172.28.25.55:9300","172.28.25.52:9300"]
#
# Prevent the "split brain" by configuring the majority of nodes (total number of master-eligible nodes / 2 + 1):
#
discovery.zen.minimum_master_nodes: 2
#
# For more information, consult the zen discovery module documentation.
#
# ---------------------------------- Gateway -----------------------------------
#
# Block initial recovery after a full cluster restart until N nodes are started:
#
#gateway.recover_after_nodes: 3
#
# For more information, consult the gateway module documentation.
#
# ---------------------------------- Various -----------------------------------
#
# Require explicit names when deleting indices:
#
action.destructive_requires_name: true
http.cors.enabled: true
http.cors.allow-origin: "*"
其中，node.name，path.data，path.logs，network.host，discovery.zen.ping.unicast.hosts根据实际情况配置；
- 配置jvm.options信息，具体如下：
## JVM configuration
################################################################
## IMPORTANT: JVM heap size
################################################################
##
## You should always set the min and max JVM heap
## size to the same value. For example, to set
## the heap to 4 GB, set:
##
## -Xms4g
## -Xmx4g
##
## See https://www.elastic.co/guide/en/elasticsearch/reference/current/heap-size.html
## for more information
##
################################################################
# Xms represents the initial size of total heap space
# Xmx represents the maximum size of total heap space
-Xms2g
-Xmx2g
################################################################
## Expert settings
################################################################
##
## All settings below this section are considered
## expert settings. Don't tamper with them unless
## you understand what you are doing
##
################################################################
## GC configuration
-XX:+UseConcMarkSweepGC
-XX:CMSInitiatingOccupancyFraction=75
-XX:+UseCMSInitiatingOccupancyOnly
## optimizations
# pre-touch memory pages used by the JVM during initialization
-XX:+AlwaysPreTouch
## basic
# explicitly set the stack size
-Xss1m
# set to headless, just in case
-Djava.awt.headless=true
# ensure UTF-8 encoding by default (e.g. filenames)
-Dfile.encoding=UTF-8
# use our provided JNA always versus the system one
-Djna.nosys=true
# turn off a JDK optimization that throws away stack traces for common
# exceptions because stack traces are important for debugging
-XX:-OmitStackTraceInFastThrow
# flags to configure Netty
-Dio.netty.noUnsafe=true
-Dio.netty.noKeySetOptimization=true
-Dio.netty.recycler.maxCapacityPerThread=0
# log4j 2
-Dlog4j.shutdownHookEnabled=false
-Dlog4j2.disable.jmx=true
-Djava.io.tmpdir=/data/tmp/elastic
## heap dumps
# generate a heap dump when an allocation from the Java heap fails
# heap dumps are created in the working directory of the JVM
-XX:+HeapDumpOnOutOfMemoryError
# specify an alternative path for heap dumps
# ensure the directory exists and has sufficient space
-XX:HeapDumpPath=/data/lib/elastic
## JDK 8 GC logging
8:-XX:+PrintGCDetails
8:-XX:+PrintGCDateStamps
8:-XX:+PrintTenuringDistribution
8:-XX:+PrintGCApplicationStoppedTime
8:-Xloggc:/data/log/elastic/gc.log
8:-XX:+UseGCLogFileRotation
8:-XX:NumberOfGCLogFiles=32
8:-XX:GCLogFileSize=64m
# JDK 9+ GC logging
9-:-Xlog:gc*,gc+age=trace,safepoint:file=/data/log/elastic/gc.log:utctime,pid,tags:filecount=32,filesize=64m
# due to internationalization enhancements in JDK 9 Elasticsearch need to set the provider to COMPAT otherwise
# time/date parsing will break in an incompatible way for some date patterns and locals
9-:-Djava.locale.providers=COMPAT
其中 -Xms -Xmx视机器实际情况而定；
- 禁用分片自动分配，执行以下命令：
curl -X PUT "localhost:9200/_cluster/settings?pretty" -H 'Content-Type: application/json' -d'
{
"persistent": {
"cluster.routing.allocation.enable": "primaries"
}
}
'
- 停止索引并执行同步刷新，执行以下命令：
curl -X POST "localhost:9200/_flush/synced?pretty"
执行同步刷新时，请检查响应以确保没有失败。失败时虽然请求本身仍返回200 OK状态，但响应正文中会列出由于挂起的索引操作而导致的失败条目。如果有失败，需要重新发出请求。
停止原集群所有节点的ElasticSearch进程，使用kill的方式执行；
启动新版的ElasticSearch
bin/elasticsearch -Ecluster.initial_master_nodes=node-1,node-2,node-3 -d
注意到启动命令中有-Ecluster.initial_master_nodes=node-1,node-2,node-3，是因为新版本首次启动，需要制定备选master列表。另外，也可以在elasticsearch.yml文件中添加以下配置：
cluster.initial_master_nodes:
- node-1
- node-2
- node-3
如果是非首次启动，则无需添加-Ecluster.initial_master_nodes=node-1,node-2,node-3参数。
- 启动后，通过
curl -X GET "localhost:9200/_cat/health?pretty"
curl -X GET "localhost:9200/_cat/nodes?pretty"
命令查看集群健康度和节点情况，如果health已为yellow说明集群已启动。
- 恢复分片分配
curl -X PUT "localhost:9200/_cluster/settings?pretty" -H 'Content-Type: application/json' -d'
{
"persistent": {
"cluster.routing.allocation.enable": null
}
}
'
此时，查看集群健康度会发现健康百分比会慢慢升高，直至100%，status会变为green，至此升级完成。
- 本升级因为变动较大，根据官方文档要求是全量升级，如果是小幅升级，可参考官方文档进行滚动升级。滚动升级时无需集群所有节点都停止服务，逐台升级即可。另外，本次升级未考虑ElasticSearch plugin的升级，如有需求，请参考官方文档。
参考文档
- https://www.elastic.co/guide/en/elasticsearch/reference/7.3/restart-upgrade.html
- https://www.elastic.co/guide/en/elasticsearch/reference/7.3/rolling-upgrades.html
- https://www.elastic.co/guide/en/elasticsearch/reference/7.3/modules-discovery-bootstrap-cluster.html