通常为了提高网站的响应速度，总是把一些经常用到的数据放到内存中，而不是放到数据库中，Redis是一个很好的Cache工具，当然了还有Memcached，这里只讲Redis。在我们的电商系统中，热点数据量往往巨大，比如单点登录、用户浏览商品的信息、用户信息、用户收藏的商品信息、短息提醒数据等等，也都用到了redis，如何使redis可以横向可伸缩扩展，这需要由多台机器协同提供服务，一台挂掉了，另一台马上顶上去，即分布式的redis集群，就对系统的性能非常重要。
　　Redis集群的几个重要特征：
　　(1).Redis 集群的分片特征在于将键空间分拆了16384个槽位，每一个节点负责其中一些槽位。
　　(2).Redis提供一定程度的可用性,可以在某个节点宕机或者不可达的情况下继续处理命令.
　　(3).Redis 集群中不存在中心（central）节点或者代理（proxy）节点， 集群的其中一个主要设计目标是达到线性可扩展性（linear scalability）。
　　(4).Redis集群要想正常工作，必须要三个主节点，在我搭建的集群环境中，三个主节点都需要有一个从节点，所以一共六个节点，通俗来讲也就是需要开启6个redis服务。
　　一、安装Redis
　　整体结构：
　　二、进群环境的配置
　　（1）在这里我就开启三台Ubuntu16.04.1，因为电脑8G的内存不够用，如果你电脑内存大可以开启4台或者更多。在这三台中我都安装好了最新版本的Redis。
　　（2）集群配置文件的修改
　　需要的文件有：
　　然后通过下面的命令把上面的文件复制到usr/redis/目录下面：
　　首先在usr目录下面创建一个redis和s2目录：sudo mkdir redis;     sudo mkdir s2
　　目录创建好后，到上面图中的目录下面，打开终端，执行：cp redis* /usr/redis/，上面图中的文件就会到usr/redis/目录下面，最后到usr/redis/目录下面，打开终端，执行sudo cp redis* /usr/redis/s2/，这是该目录下面也就会有相同的文件了。
　　修改redis.conf文件中Cluster的配置，修改如下：
　　首先由于权限的问题，我们先要切换到root身份：sudo passwd root命令，先修改root的密码，修改之后，再执行su root  接着输入你设置的root密码就可以切换到root身份，如下：
　　最后在root身份执行下图中的命令就可修改redis.conf文件：
　　这里只贴出来修改的代码：（红色标注的部分为修改部分）
　　# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
　　# bind 127.0.0.1  //注释掉
　　# Protected mode is a layer of security protection, in order to avoid that
　　# Redis instances left open on the internet are accessed and exploited.
　　#
　　# When protected mode is on and if:
　　#
　　# 1) The server is not binding explicitly to a set of addresses using the
　　#    "bind" directive.
　　# 2) No password is configured.
　　#
　　# The server only accepts connections from clients connecting from the
　　# IPv4 and IPv6 loopback addresses 127.0.0.1 and ::1, and from Unix domain
　　# sockets.
　　#
　　# By default protected mode is enabled. You should disable it only if
　　# you are sure you want clients from other hosts to connect to Redis
　　# even if no authentication is configured, nor a specific set of interfaces
　　# are explicitly listed using the "bind" directive.
　　protected-mode no //yes该为no
　　# Accept connections on the specified port, default is 6379 (IANA #815344).
　　# If port 0 is specified Redis will not listen on a TCP socket.
　　port 6379
　　# TCP listen() backlog.
　　#
　　# In high requests-per-second environments you need an high backlog in order
　　# to avoid slow clients connections issues. Note that the Linux kernel
　　# will silently truncate it to the value of /proc/sys/net/core/somaxconn so
　　# make sure to raise both the value of somaxconn and tcp_max_syn_backlog
　　# in order to get the desired effect.
　　tcp-backlog 511
　　# Unix socket.
　　#
　　# Specify the path for the Unix socket that will be used to listen for
　　# incoming connections. There is no default, so Redis will not listen
　　# on a unix socket when not specified.
　　#
　　# unixsocket /tmp/redis.sock
　　# unixsocketperm 700
　　# Close the connection after a client is idle for N seconds (0 to disable)
　　timeout 0
　　# TCP keepalive.
　　#
　　# If non-zero, use SO_KEEPALIVE to send TCP ACKs to clients in absence
　　# of communication. This is useful for two reasons:
　　#
　　# 1) Detect dead peers.
　　# 2) Take the connection alive from the point of view of network
　　#    equipment in the middle.
　　#
　　# On Linux, the specified value (in seconds) is the period used to send ACKs.
　　# Note that to close the connection the double of the time is needed.
　　# On other kernels the period depends on the kernel configuration.
　　#
　　# A reasonable value for this option is 300 seconds, which is the new
　　# Redis default starting with Redis 3.2.1.
　　tcp-keepalive 300
　　################################ REDIS CLUSTER  ###############################
　　#
　　# ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
　　# WARNING EXPERIMENTAL: Redis Cluster is considered to be stable code, however
　　# in order to mark it as "mature" we need to wait for a non trivial percentage
　　# of users to deploy it in production.
　　# ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
　　#
　　# Normal Redis instances can't be part of a Redis Cluster; only nodes that are
　　# started as cluster nodes can. In order to start a Redis instance as a
　　# cluster node enable the cluster support uncommenting the following:
　　#
　　cluster-enabled yes
　　# Every cluster node has a cluster configuration file. This file is not
　　# intended to be edited by hand. It is created and updated by Redis nodes.
　　# Every Redis Cluster node requires a different cluster configuration file.
　　# Make sure that instances running in the same system do not have
　　# overlapping cluster configuration file names.
　　#
　　cluster-config-file nodes-6379.conf
　　# Cluster node timeout is the amount of milliseconds a node must be unreachable
　　# for it to be considered in failure state.
　　# Most other internal time limits are multiple of the node timeout.
　　#
　　# cluster-node-timeout 15000
　　# A slave of a failing master will avoid to start a failover if its data
　　# looks too old.
　　#
　　# There is no simple way for a slave to actually have an exact measure of
　　# its "data age", so the following two checks are performed:
　　#
　　# 1) If there are multiple slaves able to failover, they exchange messages
　　#    in order to try to give an advantage to the slave with the best
　　#    replication offset (more data from the master processed).
　　#    Slaves will try to get their rank by offset, and apply to the start
　　#    of the failover a delay proportional to their rank.
　　#
　　# 2) Every single slave computes the time of the last interaction with
　　#    its master. This can be the last ping or command received (if the master
　　#    is still in the "connected" state), or the time that elapsed since the
　　#    disconnection with the master (if the replication link is currently down).
　　#    If the last interaction is too old, the slave will not try to failover
　　#    at all.
　　#
　　# The point "2" can be tuned by user. Specifically a slave will not perform
　　# the failover if, since the last interaction with the master, the time
　　# elapsed is greater than:
　　#
　　#   (node-timeout * slave-validity-factor) + repl-ping-slave-period
　　#
　　# So for example if node-timeout is 30 seconds, and the slave-validity-factor
　　# is 10, and assuming a default repl-ping-slave-period of 10 seconds, the
　　# slave will not try to failover if it was not able to talk with the master
　　# for longer than 310 seconds.
　　#
　　# A large slave-validity-factor may allow slaves with too old data to failover
　　# a master, while a too small value may prevent the cluster from being able to
　　# elect a slave at all.
　　#
　　# For maximum availability, it is possible to set the slave-validity-factor
　　# to a value of 0, which means, that slaves will always try to failover the
　　# master regardless of the last time they interacted with the master.
　　# (However they'll always try to apply a delay proportional to their
　　# offset rank).
　　#
　　# Zero is the only value able to guarantee that when all the partitions heal
　　# the cluster will always be able to continue.
　　#
　　# cluster-slave-validity-factor 10
　　# Cluster slaves are able to migrate to orphaned masters, that are masters
　　# that are left without working slaves. This improves the cluster ability
　　# to resist to failures as otherwise an orphaned master can't be failed over
　　# in case of failure if it has no working slaves.
　　#
　　# Slaves migrate to orphaned masters only if there are still at least a
　　# given number of other working slaves for their old master. This number
　　# is the "migration barrier". A migration barrier of 1 means that a slave
　　# will migrate only if there is at least 1 other working slave for its master
　　# and so forth. It usually reflects the number of slaves you want for every
　　# master in your cluster.
　　#
　　# Default is 1 (slaves migrate only if their masters remain with at least
　　# one slave). To disable migration just set it to a very large value.
　　# A value of 0 can be set but is useful only for debugging and dangerous
　　# in production.
　　#
　　# cluster-migration-barrier 1
　　# By default Redis Cluster nodes stop accepting queries if they detect there
　　# is at least an hash slot uncovered (no available node is serving it).
　　# This way if the cluster is partially down (for example a range of hash slots
　　# are no longer covered) all the cluster becomes, eventually, unavailable.
　　# It automatically returns available as soon as all the slots are covered again.
　　#
　　# However sometimes you want the subset of the cluster which is working,
　　# to continue to accept queries for the part of the key space that is still
　　# covered. In order to do so, just set the cluster-require-full-coverage
　　# option to no.
　　#
　　# cluster-require-full-coverage yes
　　# In order to setup your cluster make sure to read the documentation
　　# available at http://redis.io web site.
　　修改完之后 按下ESC 键，再按下  :wq!保存突出。同理，s2中的redis也是这样修改的但是，需要修改一下端口号，不能喝上面的端口号重复，s2中的端口号为6390。
　　使用相同的方式修改第二台上redis的配置：只不过在该台机器上只有一个redis服务(节点)