Redis主从用法
像MySQL一样，redis是支持主从同步的，而且也支持一主多从以及多级从结构。
主从结构，一是为了纯粹的冗余备份，二是为了提升读性能，比如很消耗性能的SORT就可以由从服务器来承担。redis的主从同步是异步进行的，这意味着主从同步不会影响主逻辑，也不会降低redis的处理性能。
主从架构中，可以考虑关闭主服务器的数据持久化功能，只让从服务器进行持久化，这样可以提高主服务器的处理性能。
在主从架构中，从服务器通常被设置为只读模式，这样可以避免从服务器的数据被误修改。但是从服务器仍然可以接受CONFIG等指令，所以还是不应该将从服务器直接暴露到不安全的网络环境中。如果必须如此，那可以考虑给重要指令进行重命名，来避免命令被外人误执行。
Redis同步原理
从服务器会向主服务器发出SYNC指令，当主服务器接到此命令后，就会调用BGSAVE指令来创建一个子进程专门进行数据持久化工作，也就是将主服务器的数据写入RDB文件中。在数据持久化期间，主服务器将执行的写指令都缓存在内存中。
在BGSAVE指令执行完成后，主服务器会将持久化好的RDB文件发送给从服务器，从服务器接到此文件后会将其存储到磁盘上，然后再将其读取到内存中。这个动作完成后，主服务器会将这段时间缓存的写指令再以redis协议的格式发送给从服务器。
另外，要说的一点是，即使有多个从服务器同时发来SYNC指令，主服务器也只会执行一次BGSAVE，然后把持久化好的RDB文件发给多个下游。在redis2.8版本之前，如果从服务器与主服务器因某些原因断开连接的话，都会进行一次主从之间的全量的数据同步；而在2.8版本之后，redis支持了效率更高的增量同步策略，这大大降低了连接断开的恢复成本。
主服务器会在内存中维护一个缓冲区，缓冲区中存储着将要发给从服务器的内容。从服务器在与主服务器出现网络瞬断之后，从服务器会尝试再次与主服务器连接，一旦连接成功，从服务器就会把“希望同步的主服务器ID”和“希望请求的数据的偏移位置（replication offset）”发送出去。主服务器接收到这样的同步请求后，首先会验证主服务器ID是否和自己的ID匹配，其次会检查“请求的偏移位置”是否存在于自己的缓冲区中，如果两者都满足的话，主服务器就会向从服务器发送增量内容。
增量同步功能，需要服务器端支持全新的PSYNC指令。这个指令，只有在redis-2.8之后才具有。
建立复制：
slaveof {masterHost} {masterPort}
从节点查看复制状态信息：
info replication
断开复制：
slaveof no one
安全性：
主节点使用requirepass参数进行密码验证，客户端使用auth命令校验，从节点的masterauth参数与主节点密码保持一致
只读：
默认情况下，从节点使用slave-read-only=yes配置为只读模式
复制支持树状结构，从节点可以复制另一个从节点，实现一层层向下的复制流。
复制原理：
1)执行slaveof后从节点只保存主节点的地址信息便直接返回，保存主节点信息
2)从节点内部通过每秒运行的定时任务维护复制相关逻辑，与主节点建立socket连接
3)从节点发送ping命令请求进行首次通信
4)权限验证
5)同步数据集，2.8以后采用新复制命令psync进行数据同步
6)命令持续复制
psync命令需要以下组件支持：
主从节点各自复制偏移量：master_repl_offset，slave_repl_offset
主节点复制积压缓冲区
主节点运行id
全量复制时间开销：
主节点bgsave时间
RDB文件网络传输时间
从节点清空数据时间
从节点加载RDB时间
可能的AOF重写时间
心跳：
主从节点在建立复制后，它们之间维护着长连接并彼此发送心跳命令
异步复制
复制可能遇到的问题：
复制数据延迟
读到过期数据
从节点故障
Redis配置主从备份及主备切换方案配置
192.168.1.101 master 6379
192.168.1.102 slave1 6379
192.168.1.103 slave2 6379
修改master文件：/etc/redis/6379.conf
pidfile /var/run/redis_6379.pid
logfile /data/logs/redis.master.log
protected-mode yes
masterauth "mypass"
requirepass "mypass"
daemonize yes
tcp-backlog 511
timeout 0
tcp-keepalive 60
loglevel notice
databases 16
dir /data
stop-writes-on-bgsave-error no
repl-timeout 60
repl-ping-slave-period 10
repl-disable-tcp-nodelay no
repl-backlog-size 10M
repl-backlog-ttl 7200
slave-serve-stale-data yes
slave-read-only yes
slave-priority 100
lua-time-limit 5000
slowlog-log-slower-than 10000
slowlog-max-len 128
hash-max-ziplist-entries 512
hash-max-ziplist-value 64
list-max-ziplist-entries 512
list-max-ziplist-value 64
set-max-intset-entries 512
zset-max-ziplist-entries 128
zset-max-ziplist-value 64
activerehashing yes
client-output-buffer-limit normal 0 0 0
client-output-buffer-limit slave 512mb 128mb 60
client-output-buffer-limit pubsub 32mb 8mb 60
hz 10
port 6379
maxmemory 512mb
maxmemory-policy volatile-lru
appendonly yes
appendfsync everysec
appendfilename appendonly-6379.aof
dbfilename dump-6379.rdb
aof-rewrite-incremental-fsync yes
no-appendfsync-on-rewrite yes
auto-aof-rewrite-min-size 64m
auto-aof-rewrite-percentage 89
rdbcompression yes
rdbchecksum yes
repl-diskless-sync no
repl-diskless-sync-delay 5
maxclients 10000
hll-sparse-max-bytes 3000
min-slaves-to-write 0
min-slaves-max-lag 10
aof-load-truncated yes
notify-keyspace-events ""
修改slave1文件：/etc/redis/6379.conf
pidfile /var/run/redis_6379.pid
logfile /data/logs/redis.slave1.log
protected-mode yes
masterauth "mypass"
requirepass "mypass"
daemonize yes
tcp-backlog 511
timeout 0
tcp-keepalive 60
loglevel notice
databases 16
dir /data
stop-writes-on-bgsave-error no
repl-timeout 60
repl-ping-slave-period 10
repl-disable-tcp-nodelay no
repl-backlog-size 10000000
repl-backlog-ttl 7200
slave-serve-stale-data yes
slave-read-only yes
slave-priority 100
lua-time-limit 5000
slowlog-log-slower-than 10000
slowlog-max-len 128
hash-max-ziplist-entries 512
hash-max-ziplist-value 64
list-max-ziplist-entries 512
list-max-ziplist-value 64
set-max-intset-entries 512
zset-max-ziplist-entries 128
zset-max-ziplist-value 64
activerehashing yes
client-output-buffer-limit normal 0 0 0
client-output-buffer-limit slave 512mb 128mb 60
client-output-buffer-limit pubsub 32mb 8mb 60
hz 10
port 6379
maxmemory 512mb
maxmemory-policy volatile-lru
appendonly yes
appendfsync everysec
appendfilename "appendonly-6379.aof"
dbfilename "dump-6379.rdb"
aof-rewrite-incremental-fsync yes
no-appendfsync-on-rewrite yes
auto-aof-rewrite-min-size 62500kb
auto-aof-rewrite-percentage 81
rdbcompression yes
rdbchecksum yes
repl-diskless-sync no
repl-diskless-sync-delay 5
maxclients 4064
hll-sparse-max-bytes 3000
min-slaves-to-write 0
min-slaves-max-lag 10
aof-load-truncated yes
notify-keyspace-events ""
slaveof 192.168.1.101 6379
修改slave2文件：/etc/redis/6379.conf
pidfile /var/run/redis_6379.pid
logfile /data/logs/redis.slave2.log
protected-mode yes
masterauth "mypass"
requirepass "mypass"
daemonize yes
tcp-backlog 511
timeout 0
tcp-keepalive 60
loglevel notice
databases 16
dir /data
stop-writes-on-bgsave-error no
repl-timeout 60
repl-ping-slave-period 10
repl-disable-tcp-nodelay no
repl-backlog-size 10000000
repl-backlog-ttl 7200
slave-serve-stale-data yes
slave-read-only yes
slave-priority 100
lua-time-limit 5000
slowlog-log-slower-than 10000
slowlog-max-len 128
hash-max-ziplist-entries 512
hash-max-ziplist-value 64
list-max-ziplist-entries 512
list-max-ziplist-value 64
set-max-intset-entries 512
zset-max-ziplist-entries 128
zset-max-ziplist-value 64
activerehashing yes
client-output-buffer-limit normal 0 0 0
client-output-buffer-limit slave 512mb 128mb 60
client-output-buffer-limit pubsub 32mb 8mb 60
hz 10
port 6379
maxmemory 512mb
maxmemory-policy volatile-lru
appendonly yes
appendfsync everysec
appendfilename "appendonly-6379.aof"
dbfilename "dump-6379.rdb"
aof-rewrite-incremental-fsync yes
no-appendfsync-on-rewrite yes
auto-aof-rewrite-min-size 62500kb
auto-aof-rewrite-percentage 81
rdbcompression yes
rdbchecksum yes
repl-diskless-sync no
repl-diskless-sync-delay 5
maxclients 4064
hll-sparse-max-bytes 3000
min-slaves-to-write 0
min-slaves-max-lag 10
aof-load-truncated yes
notify-keyspace-events ""
slaveof 192.168.1.101 6379
启动master
[root@mydb1 bin]# pwd
/usr/local/redis/bin
[root@mydb1 bin]# ./redis-server /etc/redis/6379.conf &
启动slave1
[root@mydb2 bin]# ./redis-server /etc/redis/6379.conf &
启动slave2
[root@mydb3 bin]# ./redis-server /etc/redis/6379.conf &
查看master信息
[root@mydb1 bin]# ./redis-cli -h 192.168.1.101 -p 6379 -a "mypass"
192.168.1.101:6379> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=192.168.1.102,port=6379,state=online,offset=2507,lag=0
slave1:ip=192.168.1.103,port=6379,state=online,offset=2507,lag=0
master_repl_offset:2507
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:2
repl_backlog_histlen:2506
查看slave1信息
[root@mydb2 bin]# ./redis-cli -h 192.168.1.102 -p 6379 -a "mypass"
192.168.1.102:6379> info replication
# Replication
role:slave
master_host:192.168.1.101
master_port:6379
master_link_status:up
master_last_io_seconds_ago:4
master_sync_in_progress:0
slave_repl_offset:2619
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
查看slave2信息
[root@mydb3 bin]# ./redis-cli -h 192.168.1.103 -p 6379 -a "mypass"
192.168.1.103:6379> info replication
# Replication
role:slave
master_host:192.168.1.101
master_port:6379
master_link_status:up
master_last_io_seconds_ago:6
master_sync_in_progress:0
slave_repl_offset:2703
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
测试数据同步
master上执行
192.168.1.101:6379> set name allen
OK
192.168.1.101:6379> set age 32
OK
192.168.1.101:6379> set sex male
OK
192.168.1.101:6379> set phone 13718097805
OK
192.168.1.101:6379> keys *
1) "age"
2) "name"
3) "phone"
4) "sex"
slave1上查看
192.168.1.102:6379> keys *
1) "sex"
2) "phone"
3) "age"
4) "name"
192.168.1.102:6379> get name
"allen"
slave2上查看
192.168.1.103:6379> keys *
1) "name"
2) "phone"
3) "sex"
4) "age"
192.168.1.103:6379> get name
"allen"
使用Redis Sentinel实现Redis HA
只需要设置一个sentinel配置文件如下：
/etc/redis/sentinel.conf
port 26379
bind 192.168.1.101 需要根据情况变化
protected-mode no
dir /data
logfile /data/logs/sentinel.log
sentinel monitor mymaster 192.168.1.101 6379 1
sentinel down-after-milliseconds mymaster 30000
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 18000
sentinel auth-pass mymaster mypass
启动Redis Sentinel
[root@mydb1 bin]# pwd
/usr/local/redis/bin
[root@mydb1 bin]# ./redis-sentinel /etc/redis/sentinel.conf &
[root@mydb2 bin]# ./redis-sentinel /etc/redis/sentinel.conf &
[root@mydb3 bin]# ./redis-sentinel /etc/redis/sentinel.conf &
测试：场景一：slave1宕机
192.168.1.102:6379> shutdown
not connected>
192.168.1.101:6379> info Replication
# Replication
role:master
connected_slaves:1
slave0:ip=192.168.1.103,port=6379,state=online,offset=110139,lag=0
master_repl_offset:110562
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:2
repl_backlog_histlen:110561
192.168.1.103:6379> info Replication
# Replication
role:slave
master_host:192.168.1.101
master_port:6379
master_link_status:up
master_last_io_seconds_ago:2
master_sync_in_progress:0
slave_repl_offset:113128
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
测试：场景二：slave1恢复
[root@mydb2 bin]# ./redis-server /etc/redis/6379.conf &
192.168.1.101:6379> info Replication
# Replication
role:master
connected_slaves:2
slave0:ip=192.168.1.103,port=6379,state=online,offset=139827,lag=1
slave1:ip=192.168.1.102,port=6379,state=online,offset=139968,lag=0
master_repl_offset:139968
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:2
repl_backlog_histlen:139967
192.168.1.102:6379> info Replication
# Replication
role:slave
master_host:192.168.1.101
master_port:6379
master_link_status:up
master_last_io_seconds_ago:0
master_sync_in_progress:0
slave_repl_offset:147215
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
192.168.1.103:6379> info Replication
# Replication
role:slave
master_host:192.168.1.101
master_port:6379
master_link_status:up
master_last_io_seconds_ago:1
master_sync_in_progress:0
slave_repl_offset:150627
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
测试：场景三：master宕机
192.168.1.101:6379> shutdown
not connected>
经过一段时候后
观察slave1的日志
6423:S 12 Aug 10:32:21.683 # Error condition on socket for SYNC: Connection refused
6423:S 12 Aug 10:32:22.692 * Connecting to MASTER 192.168.1.101:6379
6423:S 12 Aug 10:32:22.692 * MASTER <-> SLAVE sync started
6423:S 12 Aug 10:32:22.693 # Error condition on socket for SYNC: Connection refused
6423:M 12 Aug 10:32:22.841 * Discarding previously cached master state.
6423:M 12 Aug 10:32:22.842 * MASTER MODE enabled (user request from 'id=3 addr=192.168.1.103:41106 fd=6 name=sentinel-a409bbba-cmd age=175 idle=0 flags=x db=0 sub=0 psub=0 multi=3 qbuf=0 qbuf-free=32768 obl=36 oll=0 omem=0 events=r cmd=exec')
6423:M 12 Aug 10:32:22.843 # CONFIG REWRITE executed with success.
6423:M 12 Aug 10:32:23.857 * Slave 192.168.1.103:6379 asks for synchronization
6423:M 12 Aug 10:32:23.857 * Full resync requested by slave 192.168.1.103:6379
6423:M 12 Aug 10:32:23.857 * Starting BGSAVE for SYNC with target: disk
6423:M 12 Aug 10:32:23.858 * Background saving started by pid 6434
6434:C 12 Aug 10:32:23.903 * DB saved on disk
6434:C 12 Aug 10:32:23.903 * RDB: 6 MB of memory used by copy-on-write
6423:M 12 Aug 10:32:24.002 * Background saving terminated with success
6423:M 12 Aug 10:32:24.002 * Synchronization with slave 192.168.1.103:6379 succeeded
观察slave2的日志
6134:S 12 Aug 10:32:50.887 # Error condition on socket for SYNC: Connection refused
6134:S 12 Aug 10:32:51.895 * Connecting to MASTER 192.168.1.101:6379
6134:S 12 Aug 10:32:51.895 * MASTER <-> SLAVE sync started
6134:S 12 Aug 10:32:51.896 # Error condition on socket for SYNC: Connection refused
6134:S 12 Aug 10:32:52.665 * Discarding previously cached master state.
6134:S 12 Aug 10:32:52.665 * SLAVE OF 192.168.1.102:6379 enabled (user request from 'id=4 addr=192.168.1.103:42804 fd=7 name=sentinel-a409bbba-cmd age=264 idle=0 flags=x db=0 sub=0 psub=0 multi=3 qbuf=141 qbuf-free=32627 obl=36 oll=0 omem=0 events=r cmd=exec')
6134:S 12 Aug 10:32:52.668 # CONFIG REWRITE executed with success.
6134:S 12 Aug 10:32:52.906 * Connecting to MASTER 192.168.1.102:6379
6134:S 12 Aug 10:32:52.906 * MASTER <-> SLAVE sync started
6134:S 12 Aug 10:32:52.906 * Non blocking connect for SYNC fired the event.
6134:S 12 Aug 10:32:52.907 * Master replied to PING, replication can continue...
6134:S 12 Aug 10:32:52.908 * Partial resynchronization not possible (no cached master)
6134:S 12 Aug 10:32:52.911 * Full resync from master: 018886996edab0be5e5be9e458f1debb32b83263:1
6134:S 12 Aug 10:32:53.054 * MASTER <-> SLAVE sync: receiving 129 bytes from master
6134:S 12 Aug 10:32:53.055 * MASTER <-> SLAVE sync: Flushing old data
6134:S 12 Aug 10:32:53.055 * MASTER <-> SLAVE sync: Loading DB in memory
6134:S 12 Aug 10:32:53.055 * MASTER <-> SLAVE sync: Finished with success
观察sentinel的日志
6157:X 12 Aug 10:32:51.778 # +sdown master mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:51.778 # +odown master mymaster 192.168.1.101 6379 #quorum 1/1
6157:X 12 Aug 10:32:51.778 # +new-epoch 1
6157:X 12 Aug 10:32:51.778 # +try-failover master mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:51.782 # +vote-for-leader a409bbbafcd5dd0da5639afb4485d228aac95b78 1
6157:X 12 Aug 10:32:51.783 # +elected-leader master mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:51.783 # +failover-state-select-slave master mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:51.836 # +selected-slave slave 192.168.1.102:6379 192.168.1.102 6379 @ mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:51.836 * +failover-state-send-slaveof-noone slave 192.168.1.102:6379 192.168.1.102 6379 @ mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:51.893 * +failover-state-wait-promotion slave 192.168.1.102:6379 192.168.1.102 6379 @ mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:52.597 # +promoted-slave slave 192.168.1.102:6379 192.168.1.102 6379 @ mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:52.597 # +failover-state-reconf-slaves master mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:52.665 * +slave-reconf-sent slave 192.168.1.103:6379 192.168.1.103 6379 @ mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:53.229 * +slave-reconf-inprog slave 192.168.1.103:6379 192.168.1.103 6379 @ mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:53.229 * +slave-reconf-done slave 192.168.1.103:6379 192.168.1.103 6379 @ mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:53.306 # +failover-end master mymaster 192.168.1.101 6379
6157:X 12 Aug 10:32:53.306 # +switch-master mymaster 192.168.1.101 6379 192.168.1.102 6379
6157:X 12 Aug 10:32:53.306 * +slave slave 192.168.1.103:6379 192.168.1.103 6379 @ mymaster 192.168.1.102 6379
已经将slave1转变为master节点
192.168.1.102:6379> info replication
# Replication
role:master
connected_slaves:1
slave0:ip=192.168.1.103,port=6379,state=online,offset=19592,lag=1
master_repl_offset:19733
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:2
repl_backlog_histlen:19732
已经将原slave2转变为新master节点的slave
192.168.1.103:6379> info replication
# Replication
role:slave
master_host:192.168.1.102
master_port:6379
master_link_status:up
master_last_io_seconds_ago:0
master_sync_in_progress:0
slave_repl_offset:26500
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
测试：场景四：master恢复
[root@mydb1 bin]# ./redis-server /etc/redis/6379.conf &
当master挂掉时，sentinel会自动的从slave中挑选出一个作为master，并重新配置各redis实例的配置文件。当master重启后，sentinel会自动将它加入到当前的环境中，变成一个slave节点。
192.168.1.101:6379> info replication
# Replication
role:slave
master_host:192.168.1.102
master_port:6379
master_link_status:up
master_last_io_seconds_ago:1
master_sync_in_progress:0
slave_repl_offset:48093
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
192.168.1.102:6379> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=192.168.1.103,port=6379,state=online,offset=49108,lag=0
slave1:ip=192.168.1.101,port=6379,state=online,offset=49108,lag=0
master_repl_offset:49108
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:2
repl_backlog_histlen:49107
192.168.1.103:6379> info replication
# Replication
role:slave
master_host:192.168.1.102
master_port:6379
master_link_status:up
master_last_io_seconds_ago:1
master_sync_in_progress:0
slave_repl_offset:50250
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
当之前挂掉的master又重启后，如果希望还是还原到原先的主从配置
登录到sentinel，使用命令：
[root@mydb3 bin]## ./redis-cli -h 192.168.1.103 -p 26379
192.168.1.103:26379> sentinel failover mymaster
一主(Master)多从(Slave)，主库不开启AOF持久化，只是每天备份一下RDB[官方给的建议是每小时备份RDB文件]，而在从库上开启AOF备份，并且会用脚本将相应的备份文件推送到备份服务器。
当redis服务器挂掉时，重启时将按照以下优先级恢复数据到内存：
恢复时需要注意，要是主库挂了不能直接重启主库，否则会直接覆盖掉从库的AOF文件，一定要确保要恢复的文件都正确才能启动，否则会冲掉原来的文件。