redis 集群运行之后，难免由于硬件故障、网络规划变化、业务变化等原因对已有集群进行相应的调整， 比如: 增加节点、减少节点、节点迁移、更换服务器等。增加节点和删除节点会涉及到已有的槽位重新分配及数据迁移。
本次模拟案例：某个公司可能因为业务萎缩或主机故障，需要现有的五主五从的redis cluster架构缩小规模，我们模拟不能影响业务使用和不造成数据丢失情况下，将其动态缩容从四主四从的集群。
特别说明：一般redis集群都是3以上的偶数构成，否则容易脑裂，本实践仅演示一台机器的删除过程，同样方法可以删除第二对主从redis，实现三主三从架构。
集群维护之动态缩容过程：
先将被要删除的Redis node（IP58）上的槽位迁移到集群中的其他Redis node节点上
然后再将其（主从两个节点）删除，如果一个Redis node节点上的槽位没有被完全迁移，删除该node的时候会提示有数据且无法删除。
- 迁移槽位至其他节点
注意: 做数据迁移前一定要做好规划和数据的备份！这应该是每个SRE工程师必须记得的玉律！！！被迁移Redis master源服务器尽可能地保证没有数据在上面运行了，否则迁移过程容易出错并可能被强制中断而失败。
#### 查看所有节点和从属关系，确定好装备删除的节点
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning --cluster check 172.16.0.18:6379
172.16.0.18:6379 (d5462f69...) -> 0 keys | 3278 slots | 1 slaves.
172.16.0.28:6379 (5163e9ab...) -> 0 keys | 3278 slots | 1 slaves.
172.16.0.58:6379 (c4af78bc...) -> 0 keys | 3274 slots | 1 slaves.
172.16.0.48:6379 (aaa956c2...) -> 1 keys | 3275 slots | 1 slaves.
172.16.0.38:6379 (4c429a48...) -> 0 keys | 3279 slots | 1 slaves.
[OK] 1 keys in 5 masters.
0.00 keys per slot on average.
>>> Performing Cluster Check (using node 172.16.0.18:6379)
M: d5462f6961c0f45ecbdf12d6606e6993c33e3e29 172.16.0.18:6379
slots:[2184-5461] (3278 slots) master
1 additional replica(s)
S: 93a4ba65d181a756c08bd3b6c2a7a4d24cf5855d 172.16.0.148:6379
slots: (0 slots) slave
replicates aaa956c280b5d9fe18fca48a910c1085b5f22122
S: aeee686e355fa7784b383fec3543232126dcfbad 172.16.0.158:6379
slots: (0 slots) slave
replicates c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
M: 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e 172.16.0.28:6379
slots:[7645-10922] (3278 slots) master
1 additional replica(s)
M: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots:[1093-2183],[6553-7644],[12014-13104] (3274 slots) master
1 additional replica(s)
S: a7583f69703921c6b3d14a97f54b3015966155ab 172.16.0.118:6379
slots: (0 slots) slave
replicates d5462f6961c0f45ecbdf12d6606e6993c33e3e29
S: 3d69cddc61df9443ff7de9850c220fc9e9187c03 172.16.0.138:6379
slots: (0 slots) slave
replicates 4c429a48054a771cbc154319182a3d16cf4ce7a1
M: aaa956c280b5d9fe18fca48a910c1085b5f22122 172.16.0.48:6379
slots:[0-1092],[5462-6552],[10923-12013] (3275 slots) master
1 additional replica(s)
S: 3bbdbc3ab34b67161655974fed9de5667def8ed0 172.16.0.128:6379
slots: (0 slots) slave
replicates 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e
M: 4c429a48054a771cbc154319182a3d16cf4ce7a1 172.16.0.38:6379
slots:[13105-16383] (3279 slots) master
1 additional replica(s)
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
[root@CentOS84-IP172-18 ]#
#### 从集群中删除下面这对（主从）节点 IP58，演示缩容过程
M: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots:[1093-2183],[6553-7644],[12014-13104] (3274 slots) master
1 additional replica(s)
S: aeee686e355fa7784b383fec3543232126dcfbad 172.16.0.158:6379
slots: (0 slots) slave
replicates c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
#### 考虑五组变成四组脑裂问题，可以继续从集群中删除下面这对（主从）节点 IP48，本次仅演示删除IP58，如果要删除IP48方法相同即可。
M: aaa956c280b5d9fe18fca48a910c1085b5f22122 172.16.0.48:6379
slots:[0-1092],[5462-6552],[10923-12013] (3275 slots) master
1 additional replica(s)
S: 93a4ba65d181a756c08bd3b6c2a7a4d24cf5855d 172.16.0.148:6379
slots: (0 slots) slave
replicates aaa956c280b5d9fe18fca48a910c1085b5f22122
#### 从集群中删除下面这对（主从）节点 IP58，演示缩容过程
M: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots:[1093-2183],[6553-7644],[12014-13104] (3274 slots) master
1 additional replica(s)
S: aeee686e355fa7784b383fec3543232126dcfbad 172.16.0.158:6379
slots: (0 slots) slave
replicates c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
## 第一步先挪动了 slots:[1093-2183] 给IP18
###################################################################################
## IP172.16.0.58 上的slots:[1093-2183]迁移到 IP172.16.0.28 上去
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning --cluster reshard 172.16.0.18:6379
>>> Performing Cluster Check (using node 172.16.0.18:6379)
M: d5462f6961c0f45ecbdf12d6606e6993c33e3e29 172.16.0.18:6379
slots:[2184-5461] (3278 slots) master
1 additional replica(s)
S: 93a4ba65d181a756c08bd3b6c2a7a4d24cf5855d 172.16.0.148:6379
slots: (0 slots) slave
replicates aaa956c280b5d9fe18fca48a910c1085b5f22122
S: aeee686e355fa7784b383fec3543232126dcfbad 172.16.0.158:6379
slots: (0 slots) slave
replicates c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
M: 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e 172.16.0.28:6379
slots:[7645-10922] (3278 slots) master
1 additional replica(s)
M: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots:[1093-2183],[6553-7644],[12014-13104] (3274 slots) master
1 additional replica(s)
S: a7583f69703921c6b3d14a97f54b3015966155ab 172.16.0.118:6379
slots: (0 slots) slave
replicates d5462f6961c0f45ecbdf12d6606e6993c33e3e29
S: 3d69cddc61df9443ff7de9850c220fc9e9187c03 172.16.0.138:6379
slots: (0 slots) slave
replicates 4c429a48054a771cbc154319182a3d16cf4ce7a1
M: aaa956c280b5d9fe18fca48a910c1085b5f22122 172.16.0.48:6379
slots:[0-1092],[5462-6552],[10923-12013] (3275 slots) master
1 additional replica(s)
S: 3bbdbc3ab34b67161655974fed9de5667def8ed0 172.16.0.128:6379
slots: (0 slots) slave
replicates 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e
M: 4c429a48054a771cbc154319182a3d16cf4ce7a1 172.16.0.38:6379
slots:[13105-16383] (3279 slots) master
1 additional replica(s)
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
How many slots do you want to move (from 1 to 16384)? 1091
What is the receiving node ID? d5462f6961c0f45ecbdf12d6606e6993c33e3e29
Please enter all the source node IDs.
Type 'all' to use all the nodes as source nodes for the hash slots.
Type 'done' once you entered all the source nodes IDs.
Source node #1: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
Source node #2: done
Ready to move 1091 slots.
Source nodes:
M: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots:[1093-2183],[6553-7644],[12014-13104] (3274 slots) master
1 additional replica(s)
Destination node:
M: d5462f6961c0f45ecbdf12d6606e6993c33e3e29 172.16.0.18:6379
slots:[2184-5461] (3278 slots) master
1 additional replica(s)
Resharding plan:
Moving slot 1093 from c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
.....................
Moving slot 2183 from c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
Do you want to proceed with the proposed reshard plan (yes/no)? yes
Moving slot 1093 from 172.16.0.58:6379 to 172.16.0.18:6379:
.........................
###################################################################################
## 第二步 IP172.16.0.58 上的slots:[6553-7644] 迁移到 IP172.16.0.28 上去
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning --cluster check 172.16.0.18:6379
172.16.0.18:6379 (d5462f69...) -> 0 keys | 4369 slots | 1 slaves.
172.16.0.28:6379 (5163e9ab...) -> 0 keys | 3278 slots | 1 slaves.
172.16.0.58:6379 (c4af78bc...) -> 0 keys | 2183 slots | 1 slaves.
172.16.0.48:6379 (aaa956c2...) -> 1 keys | 3275 slots | 1 slaves.
172.16.0.38:6379 (4c429a48...) -> 0 keys | 3279 slots | 1 slaves.
[OK] 1 keys in 5 masters.
0.00 keys per slot on average.
>>> Performing Cluster Check (using node 172.16.0.18:6379)
M: d5462f6961c0f45ecbdf12d6606e6993c33e3e29 172.16.0.18:6379
slots:[1093-5461] (4369 slots) master
1 additional replica(s)
S: 93a4ba65d181a756c08bd3b6c2a7a4d24cf5855d 172.16.0.148:6379
slots: (0 slots) slave
replicates aaa956c280b5d9fe18fca48a910c1085b5f22122
S: aeee686e355fa7784b383fec3543232126dcfbad 172.16.0.158:6379
slots: (0 slots) slave
replicates c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
M: 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e 172.16.0.28:6379
slots:[7645-10922] (3278 slots) master
1 additional replica(s)
M: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots:[6553-7644],[12014-13104] (2183 slots) master
1 additional replica(s)
S: a7583f69703921c6b3d14a97f54b3015966155ab 172.16.0.118:6379
slots: (0 slots) slave
replicates d5462f6961c0f45ecbdf12d6606e6993c33e3e29
S: 3d69cddc61df9443ff7de9850c220fc9e9187c03 172.16.0.138:6379
slots: (0 slots) slave
replicates 4c429a48054a771cbc154319182a3d16cf4ce7a1
M: aaa956c280b5d9fe18fca48a910c1085b5f22122 172.16.0.48:6379
slots:[0-1092],[5462-6552],[10923-12013] (3275 slots) master
1 additional replica(s)
S: 3bbdbc3ab34b67161655974fed9de5667def8ed0 172.16.0.128:6379
slots: (0 slots) slave
replicates 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e
M: 4c429a48054a771cbc154319182a3d16cf4ce7a1 172.16.0.38:6379
slots:[13105-16383] (3279 slots) master
1 additional replica(s)
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
[root@CentOS84-IP172-18 ]#
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning --cluster reshard 172.16.0.18:6379
>>> Performing Cluster Check (using node 172.16.0.18:6379)
M: d5462f6961c0f45ecbdf12d6606e6993c33e3e29 172.16.0.18:6379
slots:[1093-5461] (4369 slots) master
1 additional replica(s)
S: 93a4ba65d181a756c08bd3b6c2a7a4d24cf5855d 172.16.0.148:6379
slots: (0 slots) slave
replicates aaa956c280b5d9fe18fca48a910c1085b5f22122
S: aeee686e355fa7784b383fec3543232126dcfbad 172.16.0.158:6379
slots: (0 slots) slave
replicates c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
M: 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e 172.16.0.28:6379
slots:[7645-10922] (3278 slots) master
1 additional replica(s)
M: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots:[6553-7644],[12014-13104] (2183 slots) master
1 additional replica(s)
S: a7583f69703921c6b3d14a97f54b3015966155ab 172.16.0.118:6379
slots: (0 slots) slave
replicates d5462f6961c0f45ecbdf12d6606e6993c33e3e29
S: 3d69cddc61df9443ff7de9850c220fc9e9187c03 172.16.0.138:6379
slots: (0 slots) slave
replicates 4c429a48054a771cbc154319182a3d16cf4ce7a1
M: aaa956c280b5d9fe18fca48a910c1085b5f22122 172.16.0.48:6379
slots:[0-1092],[5462-6552],[10923-12013] (3275 slots) master
1 additional replica(s)
S: 3bbdbc3ab34b67161655974fed9de5667def8ed0 172.16.0.128:6379
slots: (0 slots) slave
replicates 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e
M: 4c429a48054a771cbc154319182a3d16cf4ce7a1 172.16.0.38:6379
slots:[13105-16383] (3279 slots) master
1 additional replica(s)
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
How many slots do you want to move (from 1 to 16384)? 1092
What is the receiving node ID? 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e
Please enter all the source node IDs.
Type 'all' to use all the nodes as source nodes for the hash slots.
Type 'done' once you entered all the source nodes IDs.
Source node #1: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
Source node #2: done
......................
Do you want to proceed with the proposed reshard plan (yes/no)? yes
......................
###################################################################################
## 第三步 IP172.16.0.58 上的slots:[1093-5461] 迁移到 IP172.16.0.38 上去
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning --cluster check 172.16.0.18:6379
172.16.0.18:6379 (d5462f69...) -> 0 keys | 4369 slots | 1 slaves.
172.16.0.28:6379 (5163e9ab...) -> 0 keys | 4370 slots | 1 slaves.
172.16.0.58:6379 (c4af78bc...) -> 0 keys | 1091 slots | 1 slaves.
172.16.0.48:6379 (aaa956c2...) -> 1 keys | 3275 slots | 1 slaves.
172.16.0.38:6379 (4c429a48...) -> 0 keys | 3279 slots | 1 slaves.
[OK] 1 keys in 5 masters.
0.00 keys per slot on average.
>>> Performing Cluster Check (using node 172.16.0.18:6379)
M: d5462f6961c0f45ecbdf12d6606e6993c33e3e29 172.16.0.18:6379
slots:[1093-5461] (4369 slots) master
1 additional replica(s)
S: 93a4ba65d181a756c08bd3b6c2a7a4d24cf5855d 172.16.0.148:6379
slots: (0 slots) slave
replicates aaa956c280b5d9fe18fca48a910c1085b5f22122
S: aeee686e355fa7784b383fec3543232126dcfbad 172.16.0.158:6379
slots: (0 slots) slave
replicates c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
M: 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e 172.16.0.28:6379
slots:[6553-10922] (4370 slots) master
1 additional replica(s)
M: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots:[12014-13104] (1091 slots) master
1 additional replica(s)
S: a7583f69703921c6b3d14a97f54b3015966155ab 172.16.0.118:6379
slots: (0 slots) slave
replicates d5462f6961c0f45ecbdf12d6606e6993c33e3e29
S: 3d69cddc61df9443ff7de9850c220fc9e9187c03 172.16.0.138:6379
slots: (0 slots) slave
replicates 4c429a48054a771cbc154319182a3d16cf4ce7a1
M: aaa956c280b5d9fe18fca48a910c1085b5f22122 172.16.0.48:6379
slots:[0-1092],[5462-6552],[10923-12013] (3275 slots) master
1 additional replica(s)
S: 3bbdbc3ab34b67161655974fed9de5667def8ed0 172.16.0.128:6379
slots: (0 slots) slave
replicates 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e
M: 4c429a48054a771cbc154319182a3d16cf4ce7a1 172.16.0.38:6379
slots:[13105-16383] (3279 slots) master
1 additional replica(s)
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning --cluster reshard 172.16.0.18:6379
>>> Performing Cluster Check (using node 172.16.0.18:6379)
M: d5462f6961c0f45ecbdf12d6606e6993c33e3e29 172.16.0.18:6379
slots:[1093-5461] (4369 slots) master
1 additional replica(s)
S: 93a4ba65d181a756c08bd3b6c2a7a4d24cf5855d 172.16.0.148:6379
slots: (0 slots) slave
replicates aaa956c280b5d9fe18fca48a910c1085b5f22122
S: aeee686e355fa7784b383fec3543232126dcfbad 172.16.0.158:6379
slots: (0 slots) slave
replicates c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
M: 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e 172.16.0.28:6379
slots:[6553-10922] (4370 slots) master
1 additional replica(s)
M: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots:[12014-13104] (1091 slots) master
1 additional replica(s)
S: a7583f69703921c6b3d14a97f54b3015966155ab 172.16.0.118:6379
slots: (0 slots) slave
replicates d5462f6961c0f45ecbdf12d6606e6993c33e3e29
S: 3d69cddc61df9443ff7de9850c220fc9e9187c03 172.16.0.138:6379
slots: (0 slots) slave
replicates 4c429a48054a771cbc154319182a3d16cf4ce7a1
M: aaa956c280b5d9fe18fca48a910c1085b5f22122 172.16.0.48:6379
slots:[0-1092],[5462-6552],[10923-12013] (3275 slots) master
1 additional replica(s)
S: 3bbdbc3ab34b67161655974fed9de5667def8ed0 172.16.0.128:6379
slots: (0 slots) slave
replicates 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e
M: 4c429a48054a771cbc154319182a3d16cf4ce7a1 172.16.0.38:6379
slots:[13105-16383] (3279 slots) master
1 additional replica(s)
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
How many slots do you want to move (from 1 to 16384)? 1091
What is the receiving node ID? 4c429a48054a771cbc154319182a3d16cf4ce7a1
Please enter all the source node IDs.
Type 'all' to use all the nodes as source nodes for the hash slots.
Type 'done' once you entered all the source nodes IDs.
Source node #1: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
Source node #2: done
Ready to move 1091 slots.
Source nodes:
M: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots:[12014-13104] (1091 slots) master
1 additional replica(s)
Destination node:
M: 4c429a48054a771cbc154319182a3d16cf4ce7a1 172.16.0.38:6379
slots:[13105-16383] (3279 slots) master
1 additional replica(s)
Resharding plan:
Moving slot 12014 from c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
..........................
Moving slot 13104 from c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
Do you want to proceed with the proposed reshard plan (yes/no)? yes
..............................
###################################################################################
# 确认172.16.0.58 的所有slot都移走了，上面的 slave 也自动删除，成为其它 master （IP38)的 slave
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning --cluster check 172.16.0.18:6379
172.16.0.18:6379 (d5462f69...) -> 0 keys | 4369 slots | 1 slaves.
172.16.0.28:6379 (5163e9ab...) -> 0 keys | 4370 slots | 1 slaves.
172.16.0.48:6379 (aaa956c2...) -> 1 keys | 3275 slots | 1 slaves.
172.16.0.38:6379 (4c429a48...) -> 0 keys | 4370 slots | 3 slaves. #自动并入
[OK] 1 keys in 4 masters.
0.00 keys per slot on average.
>>> Performing Cluster Check (using node 172.16.0.18:6379)
M: d5462f6961c0f45ecbdf12d6606e6993c33e3e29 172.16.0.18:6379
slots:[1093-5461] (4369 slots) master
1 additional replica(s)
S: 93a4ba65d181a756c08bd3b6c2a7a4d24cf5855d 172.16.0.148:6379
slots: (0 slots) slave
replicates aaa956c280b5d9fe18fca48a910c1085b5f22122
S: aeee686e355fa7784b383fec3543232126dcfbad 172.16.0.158:6379
slots: (0 slots) slave
replicates 4c429a48054a771cbc154319182a3d16cf4ce7a1
M: 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e 172.16.0.28:6379
slots:[6553-10922] (4370 slots) master
1 additional replica(s)
S: c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 172.16.0.58:6379
slots: (0 slots) slave
replicates 4c429a48054a771cbc154319182a3d16cf4ce7a1
S: a7583f69703921c6b3d14a97f54b3015966155ab 172.16.0.118:6379
slots: (0 slots) slave
replicates d5462f6961c0f45ecbdf12d6606e6993c33e3e29
S: 3d69cddc61df9443ff7de9850c220fc9e9187c03 172.16.0.138:6379
slots: (0 slots) slave
replicates 4c429a48054a771cbc154319182a3d16cf4ce7a1
M: aaa956c280b5d9fe18fca48a910c1085b5f22122 172.16.0.48:6379
slots:[0-1092],[5462-6552],[10923-12013] (3275 slots) master
1 additional replica(s)
S: 3bbdbc3ab34b67161655974fed9de5667def8ed0 172.16.0.128:6379
slots: (0 slots) slave
replicates 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e
M: 4c429a48054a771cbc154319182a3d16cf4ce7a1 172.16.0.38:6379
slots:[12014-16383] (4370 slots) master
3 additional replica(s)
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
[root@CentOS84-IP172-18 ]#
###################################################################################
## 在IP58上也看到自动成为其他的主master redis 的从节点；IP158也自动将成了其他 主master redis 的从节点了
[root@CentOS84-IP172-58 ]#redis-cli -a 123456 --no-auth-warning info replication
# Replication
role:slave
master_host:172.16.0.38
master_port:6379
master_link_status:up
master_last_io_seconds_ago:9
master_sync_in_progress:0
slave_read_repl_offset:222208
slave_repl_offset:222208
slave_priority:100
slave_read_only:1
replica_announced:1
connected_slaves:0
master_failover_state:no-failover
master_replid:348918a6f1e9fc1b9eab3289584760767ed883b4
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:222208
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:221957
repl_backlog_histlen:252
[root@CentOS84-IP172-58 ]#
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning cluster info
cluster_state:ok
cluster_slots_assigned:16384
cluster_slots_ok:16384
cluster_slots_pfail:0
cluster_slots_fail:0
cluster_known_nodes:10 #集群中还有10个节点
cluster_size:4 #只有4对主从
cluster_current_epoch:14
cluster_my_epoch:12
cluster_stats_messages_ping_sent:160157
cluster_stats_messages_pong_sent:171005
cluster_stats_messages_sent:331162
cluster_stats_messages_ping_received:161182
cluster_stats_messages_pong_received:168889
cluster_stats_messages_meet_received:4
cluster_stats_messages_update_received:2
cluster_stats_messages_received:330077
total_cluster_links_buffer_limit_exceeded:0
[root@CentOS84-IP172-18 ]#
#### 至此IP58上的所有槽位已经全部迁移走了，可以从集群中删除主机了2. 从集群删除服务器
虽然槽位已经迁移完成，但是服务器IP信息还在集群当中，因此还需要将主机的IP信息从集群删除等。
注意: 删除服务器前,必须清除主机上面的槽位，否则会删除主机失败。
Redis 5版本以后的删除命令格式：
[root@CentOS84-IP172-58 ]#redis-cli -a <集群密码> --no-auth-warning --cluster del-node <集群中任一节点>:6379 <要删除的节点ID>
#删除节点后,redis进程自动关闭
#删除节点信息
[root@redis-node1 ~]#rm -rf /??/???/redis/nodes-6379.conf# 删除IP58节点 c4af78bc4a26490d51edc78b6c547a7abaf4e1aa 是IP58的ID信息
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning --cluster del-node 172.16.0.18:6379 c4af78bc4a26490d51edc78b6c547a7abaf4e1aa
>>> Removing node c4af78bc4a26490d51edc78b6c547a7abaf4e1aa from cluster 172.16.0.18:6379
>>> Sending CLUSTER FORGET messages to the cluster...
>>> Sending CLUSTER RESET SOFT to the deleted node.
[root@CentOS84-IP172-18 ]#
# 删除IP158节点 aeee686e355fa7784b383fec3543232126dcfbad 是IP158的ID信息
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning --cluster del-node 172.16.0.18:6379 aeee686e355fa7784b383fec3543232126dcfbad
>>> Removing node aeee686e355fa7784b383fec3543232126dcfbad from cluster 172.16.0.18:6379
>>> Sending CLUSTER FORGET messages to the cluster...
>>> Sending CLUSTER RESET SOFT to the deleted node.
[root@CentOS84-IP172-18 ]#
###################################################################################
# 登入删除节点的信息
[root@CentOS84-IP172-58 ]#find / -name nodes-6379.conf
/apps/redis/data/nodes-6379.conf
[root@CentOS84-IP172-58 ]#rm -rf /apps/redis/data/nodes-6379.conf
[root@CentOS84-IP172-158 ]#find / -name nodes-6379.conf
/apps/redis/data/nodes-6379.conf
[root@CentOS84-IP172-158 ]#rm -rf /apps/redis/data/nodes-6379.conf
[root@CentOS84-IP172-158 ]#find / -name nodes-6379.conf
[root@CentOS84-IP172-158 ]#3. 验证结果
#### 查看删除后的节点情况
###################################################################################
## 再查看相关信息
[root@CentOS84-IP172-18 ]#redis-cli -a 123456 --no-auth-warning --cluster check 172.16.0.18:6379
172.16.0.18:6379 (d5462f69...) -> 0 keys | 4369 slots | 1 slaves.
172.16.0.28:6379 (5163e9ab...) -> 0 keys | 4370 slots | 1 slaves.
172.16.0.48:6379 (aaa956c2...) -> 1 keys | 3275 slots | 1 slaves.
172.16.0.38:6379 (4c429a48...) -> 0 keys | 4370 slots | 1 slaves.
[OK] 1 keys in 4 masters.
0.00 keys per slot on average.
>>> Performing Cluster Check (using node 172.16.0.18:6379)
M: d5462f6961c0f45ecbdf12d6606e6993c33e3e29 172.16.0.18:6379
slots:[1093-5461] (4369 slots) master
1 additional replica(s)
S: 93a4ba65d181a756c08bd3b6c2a7a4d24cf5855d 172.16.0.148:6379
slots: (0 slots) slave
replicates aaa956c280b5d9fe18fca48a910c1085b5f22122
M: 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e 172.16.0.28:6379
slots:[6553-10922] (4370 slots) master
1 additional replica(s)
S: a7583f69703921c6b3d14a97f54b3015966155ab 172.16.0.118:6379
slots: (0 slots) slave
replicates d5462f6961c0f45ecbdf12d6606e6993c33e3e29
S: 3d69cddc61df9443ff7de9850c220fc9e9187c03 172.16.0.138:6379
slots: (0 slots) slave
replicates 4c429a48054a771cbc154319182a3d16cf4ce7a1
M: aaa956c280b5d9fe18fca48a910c1085b5f22122 172.16.0.48:6379
slots:[0-1092],[5462-6552],[10923-12013] (3275 slots) master
1 additional replica(s)
S: 3bbdbc3ab34b67161655974fed9de5667def8ed0 172.16.0.128:6379
slots: (0 slots) slave
replicates 5163e9abbf42bd3540d9c04f6fb384ea23a1f58e
M: 4c429a48054a771cbc154319182a3d16cf4ce7a1 172.16.0.38:6379
slots:[12014-16383] (4370 slots) master
1 additional replica(s)
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
[root@CentOS84-IP172-18 ]#redis-cli -h 172.16.0.18 -a 123456 --no-auth-warning cluster info
cluster_state:ok
cluster_slots_assigned:16384
cluster_slots_ok:16384
cluster_slots_pfail:0
cluster_slots_fail:0
cluster_known_nodes:8
cluster_size:4
cluster_current_epoch:14
cluster_my_epoch:12
cluster_stats_messages_ping_sent:161555
cluster_stats_messages_pong_sent:172378
cluster_stats_messages_sent:333933
cluster_stats_messages_ping_received:162555
cluster_stats_messages_pong_received:170287
cluster_stats_messages_meet_received:4
cluster_stats_messages_update_received:2
cluster_stats_messages_received:332848
total_cluster_links_buffer_limit_exceeded:0
[root@CentOS84-IP172-18 ]#
## 经过这样的过程,集群内有4对redis主从节点,8个主机节点
###################################################################################
#### 在删除的节点上去查看相应的服务和复制信息
[root@CentOS84-IP172-158 ]#ss -tlnp |grep redis
LISTEN 0 511 0.0.0.0:16379 0.0.0.0:* users:(("redis-server",pid=65931,fd=9))
LISTEN 0 511 0.0.0.0:6379 0.0.0.0:* users:(("redis-server",pid=65931,fd=6))
LISTEN 0 511 [::1]:16379 [::]:* users:(("redis-server",pid=65931,fd=10))
LISTEN 0 511 [::1]:6379 [::]:* users:(("redis-server",pid=65931,fd=7))
[root@CentOS84-IP172-158 ]#redis-cli -h 172.16.0.58 -a 123456 --no-auth-warning info replication
# Replication
role:master
connected_slaves:0
master_failover_state:no-failover
master_replid:4d67815feedd81d4c669d39a78f6838417304a22
master_replid2:348918a6f1e9fc1b9eab3289584760767ed883b4
master_repl_offset:223552
second_repl_offset:223553
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:221957
repl_backlog_histlen:1596
[root@CentOS84-IP172-158 ]#
###################################################################################
[root@CentOS84-IP172-18 ]#ss -tn
State Recv-Q Send-Q Local Address:Port Peer Address:Port Process
ESTAB 0 0 172.16.0.18:47751 172.16.0.118:16379
ESTAB 0 0 172.16.0.18:6379 172.16.0.118:38629
ESTAB 0 0 172.16.0.18:16379 172.16.0.28:36447
ESTAB 0 0 172.16.0.18:23045 172.16.0.48:16379
ESTAB 0 0 172.16.0.18:31225 172.16.0.148:16379
ESTAB 0 96 172.16.0.18:22 172.16.0.254:1132
ESTAB 0 0 172.16.0.18:16379 172.16.0.38:45723
ESTAB 0 0 172.16.0.18:27207 172.16.0.138:16379
ESTAB 0 0 172.16.0.18:16379 172.16.0.148:17267
ESTAB 0 0 172.16.0.18:16379 172.16.0.128:25009
ESTAB 0 0 172.16.0.18:16379 172.16.0.118:41581
ESTAB 0 0 172.16.0.18:16379 172.16.0.138:52927
ESTAB 0 0 172.16.0.18:16379 172.16.0.48:53471
ESTAB 0 0 172.16.0.18:51605 172.16.0.128:16379
ESTAB 0 0 172.16.0.18:51135 172.16.0.38:16379
ESTAB 0 0 172.16.0.18:63577 172.16.0.28:16379
[root@CentOS84-IP172-18 ]#
####至此IP58 / IP158 这对redis主机已经从集群中删除了，如果考虑到脑裂，可以将IP48 / IP148 用同样的方法删除。
