redis - 主从复制与主从切换

redis2.8之前本身是不支持分布式管理的，一般建议使用redis3.0及以后版本

redis主从切换的方法 keepalive  或者 使用sentinel线程管理

说明如何使用sentinel实现主从管理（在已经配置好主从并启动的前提下）

1、sentinel.conf 配置文件

 # Example sentinel.conf

 # port <sentinel-port>
 # The port that this sentinel instance will run on
 port
 protected-mode no

 # sentinel announce-ip <ip>
 # sentinel announce-port <port>
 #
 # The above two configuration directives are useful in environments where,
 # because of NAT, Sentinel is reachable from outside via a non-local address.
 #
 # When announce-ip is provided, the Sentinel will claim the specified IP address
 # in HELLO messages used to gossip its presence, instead of auto-detecting the
 # local address as it usually does.
 #
 # Similarly when announce-port is provided and is valid and non-zero, Sentinel
 # will announce the specified TCP port.
 #
 # The two options don't need to be used together, if only announce-ip is
 # provided, the Sentinel will announce the specified IP and the server port
 # as specified by the "port" option. If only announce-port is provided, the
 # Sentinel will announce the auto-detected local IP and the specified port.
 #
 # Example:
 #
 # sentinel announce-ip 1.2.3.4

 # dir <working-directory>
 # Every long running process should have a well-defined working directory.
 # For Redis Sentinel to chdir to /tmp at startup is the simplest thing
 # for the process to don't interfere with administrative tasks such as
 # unmounting filesystems.
 dir "/tmp"

 # sentinel monitor <master-name> <ip> <redis-port> <quorum>
 #
 # Tells Sentinel to monitor this master, and to consider it in O_DOWN
 # (Objectively Down) state only if at least <quorum> sentinels agree.
 #
 # Note that whatever is the ODOWN quorum, a Sentinel will require to
 # be elected by the majority of the known Sentinels in order to
 # start a failover, so no failover can be performed in minority.
 #
 # Slaves are auto-discovered, so you don't need to specify slaves in
 # any way. Sentinel itself will rewrite this configuration file adding
 # the slaves using additional configuration options.
 # Also note that the configuration file is rewritten when a
 # slave is promoted to master.
 #
 # Note: master name should not include special characters or spaces.
 # The valid charset is A-z - and the three characters ".-_".
 sentinel myid 920ad7dac87a4c853bbdf6417578e53ce261bdec

 # sentinel auth-pass <master-name> <password>
 #
 # Set the password to use to authenticate with the master and slaves.
 # Useful if there is a password set in the Redis instances to monitor.
 #
 # Note that the master password is also used for slaves, so it is not
 # possible to set a different password in masters and slaves instances
 # if you want to be able to monitor these instances with Sentinel.
 #
 # However you can have Redis instances without the authentication enabled
 # mixed with Redis instances requiring the authentication (as long as the
 # password set is the same for all the instances requiring the password) as
 # the AUTH command will have no effect in Redis instances with authentication
 # switched off.
 #
 # Example:
 #
 sentinel monitor mymaster 192.168.91.233  

 # sentinel down-after-milliseconds <master-name> <milliseconds>
 #
 # Number of milliseconds the master (or any attached slave or sentinel) should
 # be unreachable (as in, not acceptable reply to PING, continuously, for the
 # specified period) in order to consider it in S_DOWN state (Subjectively
 # Down).
 #
 # Default is  seconds.
 sentinel failover-timeout mymaster 

 sentinel auth-pass mymaster
 #
 # How many slaves we can reconfigure to point to the new slave simultaneously
 # during the failover. Use a low number if you use the slaves to serve query
 # to avoid that all the slaves will be unreachable at about the same
 # time while performing the synchronization with the master.
 #sentinel config-epoch mymaster 

 #sentinel leader-epoch mymaster
 #
 # Specifies the failover timeout in milliseconds. It is used in many ways:
 #
 # - The time needed to re-start a failover after a previous failover was
 #   already tried against the same master by a given Sentinel, is two
 #   times the failover timeout.
 #
 # - The time needed for a slave replicating to a wrong master according
 #   to a Sentinel current configuration, to be forced to replicate
 #   with the right master, is exactly the failover timeout (counting since
 #   the moment a Sentinel detected the misconfiguration).
 #
 # - The time needed to cancel a failover that is already in progress but
 #   did not produced any configuration change (SLAVEOF NO ONE yet not
 #   acknowledged by the promoted slave).
 #
 # - The maximum time a failover in progress waits for all the slaves to be
 #   reconfigured as slaves of the new master. However even after this time
 #   the slaves will be reconfigured by the Sentinels anyway, but not with
 #   the exact parallel-syncs progression as specified.
 #
 # Default is  minutes.
 sentinel config-epoch mymaster
 #sentinel known-slave mymaster 192.168.91.233 

 # SCRIPTS EXECUTION
 #
 # sentinel notification-script and sentinel reconfig-script are used in order
 # to configure scripts that are called to notify the system administrator
 # or to reconfigure clients after a failover. The scripts are executed
 # with the following rules for error handling:
 #
 # If script exits with "" the execution is retried later (up to a maximum
 # number of times currently set to ).
 #
 # If script exits with "" (or an higher value) the script execution is
 # not retried.
 #
 # If script terminates because it receives a signal the behavior is the same
 # as exit code .
 #
 # A script has a maximum running time of  seconds. After this limit is
 # reached the script is terminated with a SIGKILL and the execution retried.

 # NOTIFICATION SCRIPT
 #
 # sentinel notification-script <master-name> <script-path>
 #
 # Call the specified notification script for any sentinel event that is
 # generated in the WARNING level (for instance -sdown, -odown, and so forth).
 # This script should notify the system administrator via email, SMS, or any
 # other messaging system, that there is something wrong with the monitored
 # Redis systems.
 #
 # The script is called with just two arguments: the first is the event type
 # and the second the event description.
 #
 # The script must exist and be executable in order for sentinel to start if
 # this option is provided.
 #
 # Example:
 #
 # sentinel notification-script mymaster /var/redis/notify.sh

 # CLIENTS RECONFIGURATION SCRIPT
 #
 # sentinel client-reconfig-script <master-name> <script-path>
 #
 # When the master changed because of a failover a script can be called in
 # order to perform application-specific tasks to notify the clients that the
 # configuration has changed and the master is at a different address.
 #
 # The following arguments are passed to the script:
 #
 # <master-name> <role> <state> <from-ip> <from-port> <to-ip> <to-port>
 #
 # <state> is currently always "failover"
 # <role> is either "leader" or "observer"
 #
 # The arguments from-ip, from-port, to-ip, to-port are used to communicate
 # the old address of the master and the new address of the elected slave
 # (now a master).
 #
 # This script should be resistant to multiple invocations.
 #
 # Example:
 #
 # sentinel client-reconfig-script mymaster /var/redis/reconfig.sh

 # Generated by CONFIG REWRITE
 #sentinel current-epoch 

 sentinel leader-epoch mymaster
 sentinel known-slave mymaster 192.168.91.234
 sentinel current-epoch 

seninel.conf

此配置文件为实际运行的，最后的一些配置是sentinel自动写进去的，而不是配置的。

值得注意的是，需要配置protected mode为no

sentinel monitor mymaster 这个参数不要用默认的127.0.0.1  使用真实的IP地址

部分参数，在样例中是有的，但在这个配置文件中注释掉的

2、接下来启动sentinel

　　./src/redis-sentinel sentinel.conf &

3、登录sentinel

　　./src/redis-cli -h 192.168.91.234 -p 26379

　　查看主从信息：info

　　关键是最后一句：master0:name=mymaster,status=ok,address=192.168.91.234:6379,slaves=1,sentinels=1

　　status 是ok就是可用的；

　　sdown 是主观不可用，这种情况下；当足够多的sentinel检测到master为sdown后，就会将master 置为odown

　　odown 是客观不可用。

4、客户端开发，使用jedis的JedisSentinelPool连接池

　　需要引入：commons-pool2-2.4.2.jar  和   jedis-2.8.1.jar包

　　代码如下：

import java.util.HashSet;
import java.util.Set;

import org.apache.commons.pool2.impl.GenericObjectPoolConfig;
import org.junit.Test;

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisSentinelPool;

public class JedisSentinel {

    @Test
    public final void test() {
        String masterName="mymaster";
        //sentinel地址集合
        Set<String>set=new HashSet<String>();
        set.add("192.168.91.234:26379");
        GenericObjectPoolConfig gPoolConfig=new GenericObjectPoolConfig();
        gPoolConfig.setMaxIdle(10);
        gPoolConfig.setMaxTotal(10);
        gPoolConfig.setMaxWaitMillis(10);
        gPoolConfig.setJmxEnabled(true);
        JedisSentinelPool jSentinelPool=new JedisSentinelPool(masterName,set,gPoolConfig);
        //------------------------------------------
        Jedis jedis=null;
        jedis=jSentinelPool.getResource();
        jedis.auth("123456");
        //jedis.set("key1", "value2");
        String key1 = jedis.get("key1");
        System.out.println(key1);
        jedis.close();
    }

}

　　此时，当一个主redis挂掉之后，sentinel线程会改变从redis的配置文件，并使其成为主redis。当主redis启动后，会变为从redis.

　　sentinel可以配置多个，配置文件没有区别，客户端连接略有区别！

　　这样就实现了redis的主从复制、主从切换！

　　最简配置如下：

　　

port
protected-mode no

dir /tmp

sentinel monitor mymaster 192.168.37.101  

sentinel down-after-milliseconds mymaster 

sentinel parallel-syncs mymaster 

sentinel failover-timeout mymaster