Day25 Redis架构实战-Sentinel选取Replica机制

Replica选择切换机制

• 先剔除不健康的Replica

  • Replica与Master失去连线时间，或是资料落後Master太久的都会优先背剔除

• 依照Replica-priority进行排序

  • 依照Redis.conf中设定的组态，越小越优先

• 资料同步复制处理之同步差

  • 如果Replica-priority相同，则会选择与Master资料同步差异最小的优先选择

• RunID

  • 如果Replica-priority相同且资料同步差也相同，则选择RunID最小的．
  • RunID越小代表Redis Server越先启动的．

• 在开始测试Redis Server异常自动切换Master前，先确认目前Sentinel丛集状态．

# 连线到sentinel丛集
# 目前监控的redis server master是mymaster中的 IP: 127.0.0.1 Port: 6380
# Sentinel 26379 状态
./redis-cli -h 127.0.0.1 -p 26379
127.0.0.1:26379> info sentinel
# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
sentinel_simulate_failure_flags:0
master0:name=mymaster,status=ok,address=127.0.0.1:6380,slaves=2,sentinels=3

# Sentinel 26380 状态
./redis-cli -h 127.0.0.1 -p 26380
127.0.0.1:26380> info sentinel
# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
sentinel_simulate_failure_flags:0
master0:name=mymaster,status=ok,address=127.0.0.1:6380,slaves=2,sentinels=3

# Sentinel 26381 状态
./redis-cli -h 127.0.0.1 -p 26381
127.0.0.1:26381> info sentinel
# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
sentinel_simulate_failure_flags:0
master0:name=mymaster,status=ok,address=127.0.0.1:6380,slaves=2,sentinels=3

• 连线到目前Redis Server Master确认目前状态．

# 连线至目前Redis Server (Master) 6380
./redis-cli -h 127.0.0.1 -p 6380
127.0.0.1:6380> info replication
# Replication
role:master
connected_slaves:2
slave0:ip=127.0.0.1,port=6381,state=online,offset=3204281,lag=0
slave1:ip=127.0.0.1,port=6379,state=online,offset=3204281,lag=0
master_failover_state:no-failover
master_replid:ea3bc11d99568d87b0496fb83c6f2ccc58425baa
master_replid2:a30878092cdd31e404af76eaa7a2d024c8ae843e
master_repl_offset:3204281
second_repl_offset:19299
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:2155706
repl_backlog_histlen:1048576

• 找出目前Redis Server Ｍaster并让其异常终止．

# 
ps -ef|grep redis-server

# kill
kill -9 409413

• 终止目前Redis Server Master Process

• Redis Server Replica 6379 log显示内容

• Redis Server Replica 6381 log显示内容

• Sentinel 26379 log 显示侦测到Redis Server Master异常并进行Replica选举，切换Replica为Master．

• Sentinel 已将Redis Server Replica 6381切换为Master．

# 原Redis Server Master 6380 已侦测到异常
+sdown master mymaster 127.0.0.1 6380

# 投票选取Sentinel 此次进行切换的Leader
+vote-for-leader 6337212980ee71b6db0222c50ad525c94c6c48a8 1

# 选取Sentinel 26380为此次进行切换的Leader
+config-update-from sentinel 6337212980ee71b6db0222c50ad525c94c6c48a8 127.0.0.1 26380 @ mymaster 127.0.0.1 6380

# 切换Redis Server Master 6381为新的Ｍaster取代原有的
switch-master mymaster 127.0.0.1 6380 127.0.0.1 6381

• Redis Server Master 6381 显示已成为Master．

• Redis Server Replica 6379 与新的Redis Server Ｍaster 6381 建立同步．

• 将Redis Server 6380 复原重新加入丛集．

Connecting to MASTER 127.0.0.1:6381
Full resync from master: c2f5749e8daef12058d98addb48e954afbc92698:1306638

• Sentinel 会将 Redis Server 6380角色切换为Replica．

• 确认结果是否符合异常自动切换的高可用情境．

# 确认Redis Server 6380角色为Replica
./redis-cli -h 127.0.0.1 -p 6380
127.0.0.1:6380> info replication
# Replication
role:slave
master_host:127.0.0.1
master_port:6381
master_link_status:up
master_last_io_seconds_ago:0
master_sync_in_progress:0
slave_repl_offset:1377655
slave_priority:100
slave_read_only:1
replica_announced:1
connected_slaves:0
master_failover_state:no-failover
master_replid:c2f5749e8daef12058d98addb48e954afbc92698
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:1377655
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1306639
repl_backlog_histlen:71017

# 确认Sentinel与Redis Server都已恢复
./redis-cli -h 127.0.0.1 -p 26379
127.0.0.1:26379> info sentinel
# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
sentinel_simulate_failure_flags:0
master0:name=mymaster,status=ok,address=127.0.0.1:6381,slaves=2,sentinels=3