Redis叢集詳解
Redis叢集詳解
Redis有三種叢集模式，分別是：
* 主從模式
* Sentinel模式
* Cluster模式
三種叢集模式各有特點，關於Redis介紹可以參考這裡：NoSQL（二)——Redis
Redis官網：https://redis.io/ ，最新版本6.0.5
主從模式
主從模式介紹
主從模式是三種模式中最簡單的，在主從複製中，資料庫分為兩類：主資料庫(master)和從資料庫(slave)。
其中主從複製有如下特點：
* 主資料庫可以進行讀寫操作，當讀寫操作導致資料變化時會自動將資料同步給從資料庫
* 從資料庫一般都是隻讀的，並且接收主資料庫同步過來的資料
* 一個master可以擁有多個slave，但是一個slave只能對應一個master
* slave掛了不影響其他slave的讀和master的讀和寫，重新啟動後會將資料從master同步過來
* master掛了以後，不影響slave的讀，但redis不再提供寫服務，master重啟後redis將重新對外提供寫服務
* master掛了以後，不會在slave節點中重新選一個master
工作機制：
當slave啟動後，主動向master傳送SYNC命令。master接收到SYNC命令後在後臺儲存快照（RDB持久化）和快取儲存快照這段時間的命令，然後將儲存的快照檔案和快取的命令傳送給slave。slave接收到快照檔案和命令後加載快照檔案和快取的執行命令。
複製初始化後，master每次接收到的寫命令都會同步傳送給slave，保證主從資料一致性。
安全設定：
當master節點設定密碼後，
客戶端訪問master需要密碼
啟動slave需要密碼，在配置檔案中配置即可
客戶端訪問slave不需要密碼
缺點：
從上面可以看出，master節點在主從模式中唯一，若master掛掉，則redis無法對外提供寫服務。
主從模式搭建
環境準備：
master節點 192.168.30.128
slave節點 192.168.30.129
slave節點 192.168.30.130
全部下載安裝：
# cd /software # wget http://download.redis.io/releases/redis-6.0.5.tar.gz # tar zxf redis-5.0.4.tar.gz && mv redis-6.0.5/ /usr/local/redis # cd /usr/local/redis && make && make install # echo $? 0
全部配置成服務：
服務檔案
# vim /usr/lib/systemd/system/redis.service
[Unit]
Description=Redis persistent key-value database
After=network.target
After=network-online.target
Wants=network-online.target[Service]
ExecStart=/usr/local/bin/redis-server /usr/local/redis/redis.conf --supervised systemd
ExecStop=/usr/libexec/redis-shutdown
Type=notify
User=redis
Group=redis
RuntimeDirectory=redis
RuntimeDirectoryMode=0755[Install]
WantedBy=multi-user.target
shutdown指令碼
# vim /usr/libexec/redis-shutdown
#!/bin/bash
#
# Wrapper to close properly redis and sentinel
test x"$REDIS_DEBUG" != x && set -x
REDIS_CLI=/usr/local/bin/redis-cli
# Retrieve service name
SERVICE_NAME="$1"
if [ -z "$SERVICE_NAME" ]; then
SERVICE_NAME=redis
fi
# Get the proper config file based on service name
CONFIG_FILE="/usr/local/redis/$SERVICE_NAME.conf"
# Use awk to retrieve host,port from config file
HOST=`awk '/^[[:blank:]]*bind/ { print $2 }' $CONFIG_FILE | tail -n1`
PORT=`awk '/^[[:blank:]]*port/ { print $2 }' $CONFIG_FILE | tail -n1`
PASS=`awk '/^[[:blank:]]*requirepass/ { print $2 }' $CONFIG_FILE | tail -n1`
SOCK=`awk '/^[[:blank:]]*unixsocket\s/ { print $2 }' $CONFIG_FILE | tail -n1`
# Just in case,use default host,port
HOST=${HOST:-127.0.0.1}
if [ "$SERVICE_NAME" = redis ]; then
PORT=${PORT:-6379}
else
PORT=${PORT:-26739}
fi
# Setup additional parameters
# e.g password-protected redis instances
[ -z "$PASS" ] || ADDITIONAL_PARAMS="-a $PASS"
# shutdown the service properly
if [ -e "$SOCK" ] ; then
$REDIS_CLI -s $SOCK $ADDITIONAL_PARAMS shutdown
else
$REDIS_CLI -h $HOST -p $PORT $ADDITIONAL_PARAMS shutdown
fi
# chmod +x /usr/libexec/redis-shutdown # useradd -s /sbin/nologin redis # chown -R redis:redis /usr/local/redis # chown -R reids:redis /data/redis # yum install -y bash-completion && source /etc/profile #命令補全 # systemctl daemon-reload # systemctl enable redis
修改配置：
192.168.30.128
# mkdir -p /data/redis # vim /usr/local/redis/redis.conf bind 192.168.30.128 #監聽ip，多個ip用空格分隔 daemonize yes #允許後臺啟動 logfile "/usr/local/redis/redis.log" #日誌路徑 dir /data/redis #資料庫備份檔案存放目錄 masterauth 123456 #slave連線master密碼，master可省略 requirepass 123456 #設定master連線密碼，slave可省略 appendonly yes #在/data/redis/目錄生成appendonly.aof檔案，將每一次寫操作請求都追加到appendonly.aof 檔案中 # echo 'vm.overcommit_memory=1' >> /etc/sysctl.conf # sysctl -p
192.168.30.129
# mkdir -p /data/redis # vim /usr/local/redis/redis.conf bind 192.168.30.129 daemonize yes logfile "/usr/local/redis/redis.log" dir /data/redis replicaof 192.168.30.128 6379 masterauth 123456 requirepass 123456 appendonly yes # echo 'vm.overcommit_memory=1' >> /etc/sysctl.conf # sysctl -p
192.168.30.130
# mkdir -p /data/redis # vim /usr/local/redis/redis.conf bind 192.168.30.130 daemonize yes logfile "/usr/local/redis/redis.log" dir /data/redis replicaof 192.168.30.128 6379 masterauth 123456 requirepass 123456 appendonly yes # echo 'vm.overcommit_memory=1' >> /etc/sysctl.conf # sysctl -p
全部啟動redis：
# systemctl start redis
檢視叢集狀態：
# redis-cli -h 192.168.30.128 -a 123456 Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe. 192.168.30.128:6379> info replication # Replication role:master connected_slaves:2 slave0:ip=192.168.30.129,port=6379,state=online,offset=168,lag=1 slave1:ip=192.168.30.130,lag=1 master_replid:fb4941e02d5032ad74c6e2383211fc58963dbe90 master_replid2:0000000000000000000000000000000000000000 master_repl_offset:168 second_repl_offset:-1 repl_backlog_active:1 repl_backlog_size:1048576 repl_backlog_first_byte_offset:1 repl_backlog_histlen:168
# redis-cli -h 192.168.30.129 -a 123456 info replication Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe. # Replication role:slave master_host:192.168.30.128 master_port:6379 master_link_status:up master_last_io_seconds_ago:1 master_sync_in_progress:0 slave_repl_offset:196 slave_priority:100 slave_read_only:1 connected_slaves:0 master_replid:fb4941e02d5032ad74c6e2383211fc58963dbe90 master_replid2:0000000000000000000000000000000000000000 master_repl_offset:196 second_repl_offset:-1 repl_backlog_active:1 repl_backlog_size:1048576 repl_backlog_first_byte_offset:1 repl_backlog_histlen:196
資料演示：
192.168.30.128:6379> keys * (empty list or set) 192.168.30.128:6379> set key1 100 OK 192.168.30.128:6379> set key2 lzx OK 192.168.30.128:6379> keys * 1) "key1" 2) "key2"
# redis-cli -h 192.168.30.129 -a 123456 Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe. 192.168.30.129:6379> keys * 1) "key2" 2) "key1" 192.168.30.129:6379> CONFIG GET dir 1) "dir" 2) "/data/redis" 192.168.30.129:6379> CONFIG GET dbfilename 1) "dbfilename" 2) "dump.rdb" 192.168.30.129:6379> get key1 "100" 192.168.30.129:6379> get key2 "lzx" 192.168.30.129:6379> set key3 aaa (error) READONLY You can't write against a read only replica.
# redis-cli -h 192.168.30.130 -a 123456 Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe. 192.168.30.130:6379> keys * 1) "key2" 2) "key1" 192.168.30.130:6379> CONFIG GET dir 1) "dir" 2) "/data/redis" 192.168.30.130:6379> CONFIG GET dbfilename 1) "dbfilename" 2) "dump.rdb" 192.168.30.130:6379> get key1 "100" 192.168.30.130:6379> get key2 "lzx" 192.168.30.130:6379> set key3 aaa (error) READONLY You can't write against a read only replica.
可以看到，在master節點寫入的資料，很快就同步到slave節點上，而且在slave節點上無法寫入資料。
Sentinel模式
Sentinel模式介紹
主從模式的弊端就是不具備高可用性，當master掛掉以後，Redis將不能再對外提供寫入操作，因此sentinel應運而生。
sentinel中文含義為哨兵，顧名思義，它的作用就是監控redis叢集的執行狀況，特點如下：
* sentinel模式是建立在主從模式的基礎上，如果只有一個Redis節點，sentinel就沒有任何意義
* 當master掛了以後，sentinel會在slave中選擇一個做為master，並修改它們的配置檔案，其他slave的配置檔案也會被修改，比如slaveof屬性會指向新的master
* 當master重新啟動後，它將不再是master而是做為slave接收新的master的同步資料
* sentinel因為也是一個程序有掛掉的可能，所以sentinel也會啟動多個形成一個sentinel叢集
* 多sentinel配置的時候，sentinel之間也會自動監控
* 當主從模式配置密碼時，sentinel也會同步將配置資訊修改到配置檔案中，不需要擔心
* 一個sentinel或sentinel叢集可以管理多個主從Redis，多個sentinel也可以監控同一個redis
* sentinel最好不要和Redis部署在同一臺機器，不然Redis的伺服器掛了以後，sentinel也掛了
工作機制：
* 每個sentinel以每秒鐘一次的頻率向它所知的master，slave以及其他sentinel例項傳送一個 PING 命令
* 如果一個例項距離最後一次有效回覆 PING 命令的時間超過 down-after-milliseconds 選項所指定的值， 則這個例項會被sentinel標記為主觀下線。
* 如果一個master被標記為主觀下線，則正在監視這個master的所有sentinel要以每秒一次的頻率確認master的確進入了主觀下線狀態
* 當有足夠數量的sentinel（大於等於配置檔案指定的值）在指定的時間範圍內確認master的確進入了主觀下線狀態， 則master會被標記為客觀下線
* 在一般情況下， 每個sentinel會以每 10 秒一次的頻率向它已知的所有master，slave傳送 INFO 命令
* 當master被sentinel標記為客觀下線時，sentinel向下線的master的所有slave傳送 INFO 命令的頻率會從 10 秒一次改為 1 秒一次
* 若沒有足夠數量的sentinel同意master已經下線，master的客觀下線狀態就會被移除；
若master重新向sentinel的 PING 命令返回有效回覆，master的主觀下線狀態就會被移除
當使用sentinel模式的時候，客戶端就不要直接連線Redis，而是連線sentinel的ip和port，由sentinel來提供具體的可提供服務的Redis實現，這樣當master節點掛掉以後，sentinel就會感知並將新的master節點提供給使用者。
Sentinel模式搭建
環境準備：
master節點 192.168.30.128 sentinel埠：26379
slave節點 192.168.30.129 sentinel埠：26379
slave節點 192.168.30.130 sentinel埠：26379
修改配置：
前面已經下載安裝了redis，這裡省略，直接修改sentinel配置檔案。
192.168.30.128
# vim /usr/local/redis/sentinel.conf
daemonize yes
logfile "/usr/local/redis/sentinel.log"
dir "/usr/local/redis/sentinel" #sentinel工作目錄
sentinel monitor mymaster 192.168.30.128 6379 2 #判斷master失效至少需要2個sentinel同意，建議設定為n/2+1，n為sentinel個數
sentinel auth-pass mymaster 123456
sentinel down-after-milliseconds mymaster 30000 #判斷master主觀下線時間，預設30s
這裡需要注意，sentinel auth-pass mymaster 123456需要配置在sentinel monitor mymaster 192.168.30.128 6379 2下面，否則啟動報錯：
# /usr/local/bin/redis-sentinel /usr/local/redis/sentinel.conf *** FATAL CONFIG FILE ERROR *** Reading the configuration file,at line 104 >>> 'sentinel auth-pass mymaster 123456' No such master with specified name.
全部啟動sentinel：
# mkdir /usr/local/redis/sentinel && chown -R redis:redis /usr/local/redis
# /usr/local/bin/redis-sentinel /usr/local/redis/sentinel.conf
任一主機檢視日誌：
# tail -f /usr/local/redis/sentinel.log
21574:X 09 May 2019 15:32:04.298 # Sentinel ID is 30c417116a8edbab09708037366c4a7471beb770
21574:X 09 May 2019 15:32:04.298 # +monitor master mymaster 192.168.30.128 6379 quorum 2
21574:X 09 May 2019 15:32:04.299 * +slave slave 192.168.30.129:6379 192.168.30.129 6379 @ mymaster 192.168.30.128 6379
21574:X 09 May 2019 15:32:04.300 * +slave slave 192.168.30.130:6379 192.168.30.130 6379 @ mymaster 192.168.30.128 6379
21574:X 09 May 2019 15:32:16.347 * +sentinel sentinel 79b8d61626afd4d059fb5a6a63393e9a1374e78f 192.168.30.129 26379 @ mymaster 192.168.30.128 6379
21574:X 09 May 2019 15:32:31.584 * +sentinel sentinel d7b429dcba792103ef0d80827dd0910bd9284d21 192.168.30.130 26379 @ mymaster 192.168.30.128 6379
Sentinel模式下的幾個事件：
· +reset-master ：主伺服器已被重置。
· +slave ：一個新的從伺服器已經被 Sentinel 識別並關聯。
· +failover-state-reconf-slaves ：故障轉移狀態切換到了 reconf-slaves 狀態。
· +failover-detected ：另一個 Sentinel 開始了一次故障轉移操作，或者一個從伺服器轉換成了主伺服器。
· +slave-reconf-sent ：領頭（leader）的 Sentinel 向例項傳送了 [SLAVEOF](/commands/slaveof.html) 命令，為例項設定新的主伺服器。
· +slave-reconf-inprog ：例項正在將自己設定為指定主伺服器的從伺服器，但相應的同步過程仍未完成。
· +slave-reconf-done ：從伺服器已經成功完成對新主伺服器的同步。
· -dup-sentinel ：對給定主伺服器進行監視的一個或多個 Sentinel 已經因為重複出現而被移除 —— 當 Sentinel 例項重啟的時候，就會出現這種情況。
· +sentinel ：一個監視給定主伺服器的新 Sentinel 已經被識別並新增。
· +sdown ：給定的例項現在處於主觀下線狀態。
· -sdown ：給定的例項已經不再處於主觀下線狀態。
· +odown ：給定的例項現在處於客觀下線狀態。
· -odown ：給定的例項已經不再處於客觀下線狀態。
· +new-epoch ：當前的紀元（epoch）已經被更新。
· +try-failover ：一個新的故障遷移操作正在執行中，等待被大多數 Sentinel 選中（waiting to be elected by the majority）。
· +elected-leader ：贏得指定紀元的選舉，可以進行故障遷移操作了。
· +failover-state-select-slave ：故障轉移操作現在處於 select-slave 狀態 —— Sentinel 正在尋找可以升級為主伺服器的從伺服器。
· no-good-slave ：Sentinel 操作未能找到適合進行升級的從伺服器。Sentinel 會在一段時間之後再次嘗試尋找合適的從伺服器來進行升級，又或者直接放棄執行故障轉移操作。
· selected-slave ：Sentinel 順利找到適合進行升級的從伺服器。
· failover-state-send-slaveof-noone ：Sentinel 正在將指定的從伺服器升級為主伺服器，等待升級功能完成。
· failover-end-for-timeout ：故障轉移因為超時而中止，不過最終所有從伺服器都會開始複製新的主伺服器（slaves will eventually be configured to replicate with the new master anyway）。
· failover-end ：故障轉移操作順利完成。所有從伺服器都開始複製新的主伺服器了。
· +switch-master ：配置變更，主伺服器的 IP 和地址已經改變。 這是絕大多數外部使用者都關心的資訊。
· +tilt ：進入 tilt 模式。
· -tilt ：退出 tilt 模式。
master宕機演示：
192.168.30.128
# systemctl stop redis
# tail -f /usr/local/redis/sentinel.log
22428:X 09 May 2019 15:51:29.287 # +sdown master mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:29.371 # +odown master mymaster 192.168.30.128 6379 #quorum 2/2
22428:X 09 May 2019 15:51:29.371 # +new-epoch 1
22428:X 09 May 2019 15:51:29.371 # +try-failover master mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:29.385 # +vote-for-leader 30c417116a8edbab09708037366c4a7471beb770 1
22428:X 09 May 2019 15:51:29.403 # d7b429dcba792103ef0d80827dd0910bd9284d21 voted for 30c417116a8edbab09708037366c4a7471beb770 1
22428:X 09 May 2019 15:51:29.408 # 79b8d61626afd4d059fb5a6a63393e9a1374e78f voted for 30c417116a8edbab09708037366c4a7471beb770 1
22428:X 09 May 2019 15:51:29.451 # +elected-leader master mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:29.451 # +failover-state-select-slave master mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:29.528 # +selected-slave slave 192.168.30.129:6379 192.168.30.129 6379 @ mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:29.528 * +failover-state-send-slaveof-noone slave 192.168.30.129:6379 192.168.30.129 6379 @ mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:29.594 * +failover-state-wait-promotion slave 192.168.30.129:6379 192.168.30.129 6379 @ mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:30.190 # +promoted-slave slave 192.168.30.129:6379 192.168.30.129 6379 @ mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:30.190 # +failover-state-reconf-slaves master mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:30.258 * +slave-reconf-sent slave 192.168.30.130:6379 192.168.30.130 6379 @ mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:30.511 # -odown master mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:31.233 * +slave-reconf-inprog slave 192.168.30.130:6379 192.168.30.130 6379 @ mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:31.233 * +slave-reconf-done slave 192.168.30.130:6379 192.168.30.130 6379 @ mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:31.297 # +failover-end master mymaster 192.168.30.128 6379
22428:X 09 May 2019 15:51:31.297 # +switch-master mymaster 192.168.30.128 6379 192.168.30.129 6379
22428:X 09 May 2019 15:51:31.298 * +slave slave 192.168.30.130:6379 192.168.30.130 6379 @ mymaster 192.168.30.129 6379
22428:X 09 May 2019 15:51:31.298 * +slave slave 192.168.30.128:6379 192.168.30.128 6379 @ mymaster 192.168.30.129 6379
22428:X 09 May 2019 15:52:31.307 # +sdown slave 192.168.30.128:6379 192.168.30.128 6379 @ mymaster 192.168.30.129 6379
從日誌中可以看到，master已經從192.168.30.128轉移到192.168.30.129上
192.168.30.129上檢視叢集資訊
# /usr/local/bin/redis-cli -h 192.168.30.129 -p 6379 -a 123456 Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe. 192.168.30.129:6379> info replication # Replication role:master connected_slaves:1 slave0:ip=192.168.30.130,offset=291039,lag=1 master_replid:757aff269236ed2707ba584a86a40716c1c76d74 master_replid2:47a862fc0ff20362be29096ecdcca6d432070ee9 master_repl_offset:291182 second_repl_offset:248123 repl_backlog_active:1 repl_backlog_size:1048576 repl_backlog_first_byte_offset:1 repl_backlog_histlen:291182 192.168.30.129:6379> set key4 linux OK
當前叢集中只有一個slave——192.168.30.130，master是192.168.30.129，且192.168.30.129具有寫許可權。
192.168.30.130上檢視redis的配置檔案也可以看到replicaof 192.168.30.129 6379，這是sentinel在選舉master是做的修改。
重新把192.168.30.128上程序啟動
# systemctl start redis
# tail -f /usr/local/redis/sentinel.log
22428:X 09 May 2019 15:51:31.297 # +switch-master mymaster 192.168.30.128 6379 192.168.30.129 6379
22428:X 09 May 2019 15:51:31.298 * +slave slave 192.168.30.130:6379 192.168.30.130 6379 @ mymaster 192.168.30.129 6379
22428:X 09 May 2019 15:51:31.298 * +slave slave 192.168.30.128:6379 192.168.30.128 6379 @ mymaster 192.168.30.129 6379
22428:X 09 May 2019 15:52:31.307 # +sdown slave 192.168.30.128:6379 192.168.30.128 6379 @ mymaster 192.168.30.129 6379
22428:X 09 May 2019 16:01:24.872 # -sdown slave 192.168.30.128:6379 192.168.30.128 6379 @ mymaster 192.168.30.129 6379
檢視叢集資訊
# /usr/local/bin/redis-cli -h 192.168.30.128 -p 6379 -a 123456 Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe. 192.168.30.128:6379> info replication # Replication role:slave master_host:192.168.30.129 master_port:6379 master_link_status:up master_last_io_seconds_ago:0 master_sync_in_progress:0 slave_repl_offset:514774 slave_priority:100 slave_read_only:1 connected_slaves:0 master_replid:757aff269236ed2707ba584a86a40716c1c76d74 master_replid2:0000000000000000000000000000000000000000 master_repl_offset:514774 second_repl_offset:-1 repl_backlog_active:1 repl_backlog_size:1048576 repl_backlog_first_byte_offset:376528 repl_backlog_histlen:138247 192.168.30.128:6379> get key4 "linux" 192.168.30.128:6379> set key5 (error) ERR wrong number of arguments for 'set' command
即使192.168.30.128重新啟動redis服務，也是作為slave加入redis叢集，192.168.30.129仍然是master。
Cluster模式
Cluster模式介紹
sentinel模式基本可以滿足一般生產的需求，具備高可用性。但是當資料量過大到一臺伺服器存放不下的情況時，主從模式或sentinel模式就不能滿足需求了，這個時候需要對儲存的資料進行分片，將資料儲存到多個Redis例項中。cluster模式的出現就是為了解決單機Redis容量有限的問題，將Redis的資料根據一定的規則分配到多臺機器。
cluster可以說是sentinel和主從模式的結合體，通過cluster可以實現主從和master重選功能，所以如果配置兩個副本三個分片的話，就需要六個Redis例項。因為Redis的資料是根據一定規則分配到cluster的不同機器的，當資料量過大時，可以新增機器進行擴容。
使用叢集，只需要將redis配置檔案中的cluster-enable配置開啟即可。每個叢集中至少需要三個主資料庫才能正常執行，新增節點非常方便。
cluster叢集特點：
* 多個redis節點網路互聯，資料共享
* 所有的節點都是一主一從（也可以是一主多從），其中從不提供服務，僅作為備用
* 不支援同時處理多個key（如MSET/MGET），因為redis需要把key均勻分佈在各個節點上，
併發量很高的情況下同時建立key-value會降低效能並導致不可預測的行為
* 支援線上增加、刪除節點* 客戶端可以連線任何一個主節點進行讀寫
Cluster模式搭建
環境準備：
三臺機器，分別開啟兩個redis服務（埠）
192.168.30.128 埠：7001,7002
192.168.30.129 埠：7003,7004
192.168.30.130 埠：7005,7006
修改配置檔案：
192.168.30.128
# mkdir /usr/local/redis/cluster
# cp /usr/local/redis/redis.conf /usr/local/redis/cluster/redis_7001.conf
# cp /usr/local/redis/redis.conf /usr/local/redis/cluster/redis_7002.conf
# chown -R redis:redis /usr/local/redis
# mkdir -p /data/redis/cluster/{redis_7001,redis_7002} && chown -R redis:redis /data/redis
# vim /usr/local/redis/cluster/redis_7001.conf bind 192.168.30.128 port 7001 daemonize yes pidfile "/var/run/redis_7001.pid" logfile "/usr/local/redis/cluster/redis_7001.log" dir "/data/redis/cluster/redis_7001" #replicaof 192.168.30.129 6379 masterauth 123456 requirepass 123456 appendonly yes cluster-enabled yes cluster-config-file nodes_7001.conf cluster-node-timeout 15000
# vim /usr/local/redis/cluster/redis_7002.conf bind 192.168.30.128 port 7002 daemonize yes pidfile "/var/run/redis_7002.pid" logfile "/usr/local/redis/cluster/redis_7002.log" dir "/data/redis/cluster/redis_7002" #replicaof 192.168.30.129 6379 masterauth "123456" requirepass "123456" appendonly yes cluster-enabled yes cluster-config-file nodes_7002.conf cluster-node-timeout 15000
其它兩臺機器配置與192.168.30.128一致，此處省略
啟動redis服務：
# redis-server /usr/local/redis/cluster/redis_7001.conf
# tail -f /usr/local/redis/cluster/redis_7001.log
# redis-server /usr/local/redis/cluster/redis_7002.conf
# tail -f /usr/local/redis/cluster/redis_7002.log
其它兩臺機器啟動與192.168.30.128一致，此處省略
安裝ruby並建立叢集（低版本）：
如果redis版本比較低，則需要安裝ruby。任選一臺機器安裝ruby即可
# yum -y groupinstall "Development Tools"
# yum install -y gdbm-devel libdb4-devel libffi-devel libyaml libyaml-devel ncurses-devel openssl-devel readline-devel tcl-devel
# mkdir -p ~/rpmbuild/{BUILD,BUILDROOT,RPMS,SOURCES,SPECS,SRPMS}
# wget http://cache.ruby-lang.org/pub/ruby/2.2/ruby-2.2.3.tar.gz -P ~/rpmbuild/SOURCES
# wget http://raw.githubusercontent.com/tjinjin/automate-ruby-rpm/master/ruby22x.spec -P ~/rpmbuild/SPECS
# rpmbuild -bb ~/rpmbuild/SPECS/ruby22x.spec
# rpm -ivh ~/rpmbuild/RPMS/x86_64/ruby-2.2.3-1.el7.x86_64.rpm
# gem install redis #目的是安裝這個，用於配置叢集
# cp /usr/local/redis/src/redis-trib.rb /usr/bin/
# redis-trib.rb create --replicas 1 192.168.30.128:7001 192.168.30.128:7002 192.168.30.129:7003 192.168.30.129:7004 192.168.30.130:7005 192.168.30.130:7006
建立叢集：
我這裡是redis6.0.5，所以不需要安裝ruby，直接建立叢集即可
# redis-cli -a 123456 --cluster create 192.168.30.128:7001 192.168.30.128:7002 192.168.30.129:7003 192.168.30.129:7004 192.168.30.130:7005 192.168.30.130:7006 --cluster-replicas 1 Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe. >>> Performing hash slots allocation on 6 nodes... Master[0] -> Slots 0 - 5460 Master[1] -> Slots 5461 - 10922 Master[2] -> Slots 10923 - 16383 Adding replica 192.168.30.129:7004 to 192.168.30.128:7001 Adding replica 192.168.30.130:7006 to 192.168.30.129:7003 Adding replica 192.168.30.128:7002 to 192.168.30.130:7005 M: 80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001 slots:[0-5460] (5461 slots) master S: b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002 replicates 6788453ee9a8d7f72b1d45a9093838efd0e501f1 M: 4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003 slots:[5461-10922] (5462 slots) master S: b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004 replicates 80c80a3f3e33872c047a8328ad579b9bea001ad8 M: 6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005 slots:[10923-16383] (5461 slots) master S: 277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006 replicates 4d74ec66e898bf09006dac86d4928f9fad81f373 Can I set the above configuration? (type 'yes' to accept): yes #輸入yes，接受上面配置 >>> Nodes configuration updated >>> Assign a different config epoch to each node >>> Sending CLUSTER MEET messages to join the cluster
可以看到，
192.168.30.128:7001是master，它的slave是192.168.30.129:7004；
192.168.30.129:7003是master，它的slave是192.168.30.130:7006；
192.168.30.130:7005是master，它的slave是192.168.30.128:7002
自動生成nodes.conf檔案：
# ls /data/redis/cluster/redis_7001/ appendonly.aof dump.rdb nodes-7001.conf # vim /data/redis/cluster/redis_7001/nodes-7001.conf 6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557454406312 5 connected 10923-16383 277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557454407000 6 connected b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave 6788453ee9a8d7f72b1d45a9093838efd0e501f1 0 1557454408371 5 connected 80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 myself,master - 0 1557454406000 1 connected 0-5460 b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 slave 80c80a3f3e33872c047a8328ad579b9bea001ad8 0 1557454407366 4 connected 4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 master - 0 1557454407000 3 connected 5461-10922 vars currentEpoch 6 lastVoteEpoch 0
叢集操作
登入叢集：
# redis-cli -c -h 192.168.30.128 -p 7001 -a 123456 # -c，使用叢集方式登入
檢視叢集資訊：
192.168.30.128:7001> CLUSTER INFO #叢集狀態
cluster_state:ok
cluster_slots_assigned:16384
cluster_slots_ok:16384
cluster_slots_pfail:0
cluster_slots_fail:0
cluster_known_nodes:6
cluster_size:3
cluster_current_epoch:6
cluster_my_epoch:1
cluster_stats_messages_ping_sent:580
cluster_stats_messages_pong_sent:551
cluster_stats_messages_sent:1131
cluster_stats_messages_ping_received:546
cluster_stats_messages_pong_received:580
cluster_stats_messages_meet_received:5
cluster_stats_messages_received:1131
列出節點資訊：
192.168.30.128:7001> CLUSTER NODES #列出節點資訊 6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557455176000 5 connected 10923-16383 277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557455174000 6 connected b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave 6788453ee9a8d7f72b1d45a9093838efd0e501f1 0 1557455175000 5 connected 80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 myself,master - 0 1557455175000 1 connected 0-5460 b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 slave 80c80a3f3e33872c047a8328ad579b9bea001ad8 0 1557455174989 4 connected 4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 master - 0 1557455175995 3 connected 5461-10922
這裡與nodes.conf檔案內容相同
寫入資料：
192.168.30.128:7001> set key111 aaa -> Redirected to slot [13680] located at 192.168.30.130:7005 #說明資料到了192.168.30.130:7005上 OK 192.168.30.130:7005> set key222 bbb -> Redirected to slot [2320] located at 192.168.30.128:7001 #說明資料到了192.168.30.128:7001上 OK 192.168.30.128:7001> set key333 ccc -> Redirected to slot [7472] located at 192.168.30.129:7003 #說明資料到了192.168.30.129:7003上 OK 192.168.30.129:7003> get key111 -> Redirected to slot [13680] located at 192.168.30.130:7005 "aaa" 192.168.30.130:7005> get key333 -> Redirected to slot [7472] located at 192.168.30.129:7003 "ccc" 192.168.30.129:7003>
可以看出redis cluster叢集是去中心化的，每個節點都是平等的，連線哪個節點都可以獲取和設定資料。
當然，平等指的是master節點，因為slave節點根本不提供服務，只是作為對應master節點的一個備份。
增加節點：
192.168.30.129上增加一節點：
# cp /usr/local/redis/cluster/redis_7003.conf /usr/local/redis/cluster/redis_7007.conf # vim /usr/local/redis/cluster/redis_7007.conf bind 192.168.30.129 port 7007 daemonize yes pidfile "/var/run/redis_7007.pid" logfile "/usr/local/redis/cluster/redis_7007.log" dir "/data/redis/cluster/redis_7007" #replicaof 192.168.30.129 6379 masterauth "123456" requirepass "123456" appendonly yes cluster-enabled yes cluster-config-file nodes_7007.conf cluster-node-timeout 15000 # mkdir /data/redis/cluster/redis_7007 # chown -R redis:redis /usr/local/redis && chown -R redis:redis /data/redis # redis-server /usr/local/redis/cluster/redis_7007.conf
192.168.30.130上增加一節點：
# cp /usr/local/redis/cluster/redis_7005.conf /usr/local/redis/cluster/redis_7008.conf # vim /usr/local/redis/cluster/redis_7007.conf bind 192.168.30.130 port 7008 daemonize yes pidfile "/var/run/redis_7008.pid" logfile "/usr/local/redis/cluster/redis_7008.log" dir "/data/redis/cluster/redis_7008" #replicaof 192.168.30.130 6379 masterauth "123456" requirepass "123456" appendonly yes cluster-enabled yes cluster-config-file nodes_7008.conf cluster-node-timeout 15000 # mkdir /data/redis/cluster/redis_7008 # chown -R redis:redis /usr/local/redis && chown -R redis:redis /data/redis # redis-server /usr/local/redis/cluster/redis_7008.conf
叢集中增加節點：
192.168.30.129:7003> CLUSTER MEET 192.168.30.129 7007 OK 192.168.30.129:7003> CLUSTER NODES 4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 myself,master - 0 1557457361000 3 connected 5461-10922 80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 master - 0 1557457364746 1 connected 0-5460 277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557457362000 6 connected b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 slave 80c80a3f3e33872c047a8328ad579b9bea001ad8 0 1557457363000 4 connected b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave 6788453ee9a8d7f72b1d45a9093838efd0e501f1 0 1557457362000 5 connected e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 192.168.30.129:7007@17007 master - 0 1557457362729 0 connected 6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557457363739 5 connected 10923-16383
192.168.30.129:7003> CLUSTER MEET 192.168.30.130 7008 OK 192.168.30.129:7003> CLUSTER NODES 4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 myself,master - 0 1557457489000 3 connected 5461-10922 80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 master - 0 1557457489000 1 connected 0-5460 277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557457489000 6 connected b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 slave 80c80a3f3e33872c047a8328ad579b9bea001ad8 0 1557457488000 4 connected b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave 6788453ee9a8d7f72b1d45a9093838efd0e501f1 0 1557457489472 5 connected 1a1c7f02fce87530bd5abdfc98df1cffce4f1767 192.168.30.130:7008@17008 master - 0 1557457489259 0 connected e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 192.168.30.129:7007@17007 master - 0 1557457489000 0 connected 6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557457490475 5 connected 10923-16383
可以看到，新增的節點都是以master身份加入叢集的
更換節點身份：
將新增的192.168.30.130:7008節點身份改為192.168.30.129:7007的slave
# redis-cli -c -h 192.168.30.130 -p 7008 -a 123456 cluster replicate e51ab166bc0f33026887bcf8eba0dff3d5b0bf14
cluster replicate後面跟node_id，更改對應節點身份。也可以登入叢集更改
# redis-cli -c -h 192.168.30.130 -p 7008 -a 123456 192.168.30.130:7008> CLUSTER REPLICATE e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 OK 192.168.30.130:7008> CLUSTER NODES 277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557458316881 3 connected 80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 master - 0 1557458314864 1 connected 0-5460 4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 master - 0 1557458316000 3 connected 5461-10922 6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557458315872 5 connected 10923-16383 b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave 6788453ee9a8d7f72b1d45a9093838efd0e501f1 0 1557458317890 5 connected 1a1c7f02fce87530bd5abdfc98df1cffce4f1767 192.168.30.130:7008@17008 myself,slave e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 0 1557458315000 7 connected b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 slave 80c80a3f3e33872c047a8328ad579b9bea001ad8 0 1557458315000 1 connected e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 192.168.30.129:7007@17007 master - 0 1557458314000 0 connected
檢視相應的nodes.conf檔案，可以發現有更改，它記錄當前叢集的節點資訊
# cat /data/redis/cluster/redis_7001/nodes-7001.conf
1a1c7f02fce87530bd5abdfc98df1cffce4f1767 192.168.30.130:7008@17008 slave e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 0 1557458236169 7 connected
6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557458235000 5 connected 10923-16383
277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557458234103 6 connected
b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave 6788453ee9a8d7f72b1d45a9093838efd0e501f1 0 1557458235129 5 connected
80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 myself,master - 0 1557458234000 1 connected 0-5460
b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 slave 80c80a3f3e33872c047a8328ad579b9bea001ad8 0 1557458236000 4 connected
e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 192.168.30.129:7007@17007 master - 0 1557458236000 0 connected
4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 master - 0 1557458233089 3 connected 5461-10922
vars currentEpoch 7 lastVoteEpoch 0
刪除節點：
192.168.30.130:7008> CLUSTER FORGET 1a1c7f02fce87530bd5abdfc98df1cffce4f1767
(error) ERR I tried hard but I can't forget myself... #無法刪除登入節點192.168.30.130:7008> CLUSTER FORGET e51ab166bc0f33026887bcf8eba0dff3d5b0bf14
(error) ERR Can't forget my master! #不能刪除自己的master節點192.168.30.130:7008> CLUSTER FORGET 6788453ee9a8d7f72b1d45a9093838efd0e501f1
OK #可以刪除其它的master節點192.168.30.130:7008> CLUSTER NODES
277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557458887328 3 connected
80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 master - 0 1557458887000 1 connected 0-5460
4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 master - 0 1557458886000 3 connected 5461-10922
b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave - 0 1557458888351 5 connected
1a1c7f02fce87530bd5abdfc98df1cffce4f1767 192.168.30.130:7008@17008 myself,slave e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 0 1557458885000 7 connected
b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 slave 80c80a3f3e33872c047a8328ad579b9bea001ad8 0 1557458883289 1 connected
e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 192.168.30.129:7007@17007 master - 0 1557458885310 0 connected192.168.30.130:7008> CLUSTER FORGET b4d3eb411a7355d4767c6c23b4df69fa183ef8bc
OK #可以刪除其它的slave節點192.168.30.130:7008> CLUSTER NODES
277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557459031397 3 connected
80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 master - 0 1557459032407 1 connected 0-5460
4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 master - 0 1557459035434 3 connected 5461-10922
6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557459034000 5 connected 10923-16383
1a1c7f02fce87530bd5abdfc98df1cffce4f1767 192.168.30.130:7008@17008 myself,slave e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 0 1557459032000 7 connected
b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 slave 80c80a3f3e33872c047a8328ad579b9bea001ad8 0 1557459034000 1 connected
e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 192.168.30.129:7007@17007 master - 0 1557459034427 0 connected
儲存配置：
192.168.30.130:7008> CLUSTER SAVECONFIG #將節點配置資訊儲存到硬碟
OK
# cat /data/redis/cluster/redis_7001/nodes-7001.conf1a1c7f02fce87530bd5abdfc98df1cffce4f1767 192.168.30.130:7008@17008 slave e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 0 1557458236169 7 connected
6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557458235000 5 connected 10923-16383
277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557458234103 6 connected
b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave 6788453ee9a8d7f72b1d45a9093838efd0e501f1 0 1557458235129 5 connected
80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 myself,master - 0 1557458234000 1 connected 0-5460
b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 slave 80c80a3f3e33872c047a8328ad579b9bea001ad8 0 1557458236000 4 connected
e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 192.168.30.129:7007@17007 master - 0 1557458236000 0 connected
4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 master - 0 1557458233089 3 connected 5461-10922
vars currentEpoch 7 lastVoteEpoch 0# redis-cli -c -h 192.168.30.130 -p 7008 -a 123456
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.192.168.30.130:7008> CLUSTER NODES
277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557459500741 3 connected
80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 master - 0 1557459500000 1 connected 0-5460
4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 master - 0 1557459501000 3 connected 5461-10922
6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557459500000 5 connected 10923-16383
b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave 6788453ee9a8d7f72b1d45a9093838efd0e501f1 0 1557459499737 5 connected
1a1c7f02fce87530bd5abdfc98df1cffce4f1767 192.168.30.130:7008@17008 myself,slave e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 0 1557459499000 7 connected
b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 slave 80c80a3f3e33872c047a8328ad579b9bea001ad8 0 1557459501750 1 connected
e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 192.168.30.129:7007@17007 master - 0 1557459498000 0 connected
可以看到，之前刪除的節點又恢復了，這是因為對應的配置檔案沒有刪除，執行CLUSTER SAVECONFIG恢復。
模擬master節點掛掉：
192.168.30.128
# netstat -lntp |grep 7001 tcp 0 0 192.168.30.128:17001 0.0.0.0:* LISTEN 6701/redis-server 1 tcp 0 0 192.168.30.128:7001 0.0.0.0:* LISTEN 6701/redis-server 1 # kill 6701
192.168.30.130:7008> CLUSTER NODES
277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557461178000 3 connected
80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 master,fail - 1557460950483 1557460947145 1 disconnected
4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 master - 0 1557461174922 3 connected 5461-10922
6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557461181003 5 connected 10923-16383
b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave 6788453ee9a8d7f72b1d45a9093838efd0e501f1 0 1557461179993 5 connected
1a1c7f02fce87530bd5abdfc98df1cffce4f1767 192.168.30.130:7008@17008 myself,slave e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 0 1557461176000 7 connected
b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 master - 0 1557461178981 8 connected 0-5460
e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 192.168.30.129:7007@17007 master - 0 1557461179000 0 connected
對應7001的一行可以看到，master fail，狀態為disconnected；而對應7004的一行，slave已經變成master。
重新啟動7001節點：
# redis-server /usr/local/redis/cluster/redis_7001.conf 192.168.30.130:7008> CLUSTER NODES 277daeb8660d5273b7c3e05c263f861ed5f17b92 192.168.30.130:7006@17006 slave 4d74ec66e898bf09006dac86d4928f9fad81f373 0 1557461307000 3 connected 80c80a3f3e33872c047a8328ad579b9bea001ad8 192.168.30.128:7001@17001 slave b6331cbc986794237c83ed2d5c30777c1551546e 0 1557461305441 8 connected 4d74ec66e898bf09006dac86d4928f9fad81f373 192.168.30.129:7003@17003 master - 0 1557461307962 3 connected 5461-10922 6788453ee9a8d7f72b1d45a9093838efd0e501f1 192.168.30.130:7005@17005 master - 0 1557461304935 5 connected 10923-16383 b4d3eb411a7355d4767c6c23b4df69fa183ef8bc 192.168.30.128:7002@17002 slave 6788453ee9a8d7f72b1d45a9093838efd0e501f1 0 1557461306000 5 connected 1a1c7f02fce87530bd5abdfc98df1cffce4f1767 192.168.30.130:7008@17008 myself,slave e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 0 1557461305000 7 connected b6331cbc986794237c83ed2d5c30777c1551546e 192.168.30.129:7004@17004 master - 0 1557461308972 8 connected 0-5460 e51ab166bc0f33026887bcf8eba0dff3d5b0bf14 192.168.30.129:7007@17007 master - 0 1557461307000 0 connected
可以看到，7001節點啟動後為slave節點，並且是7004的slave節點。即master節點如果掛掉，它的slave節點變為新master節點繼續對外提供服務，而原來的master節點如果重啟，則變為新master節點的slave節點。
另外，如果這裡是拿7007節點做測試的話，會發現7008節點並不會切換，這是因為7007節點上根本沒資料。叢集資料被分為三份，採用雜湊槽 (hash slot)的方式來分配16384個slot的話，它們三個節點分別承擔的slot 區間是：
節點7004覆蓋0－5460
節點7003覆蓋5461－10922
節點7005覆蓋10923－16383
更多參考：
Redis叢集常用命令