Docker Swarm節點的清空（Drain）和在啟用

所有的active節點，都可以接收task。有時候會遇到，一個節點需要維護暫時不能使用，這意味着此節點將不能再接受新的task，且原有的task也要遷走，在其他可用的節點上運行

【注】將節點設置為DRAIN並不會從該節點刪除獨立容器（docker run/ docker up/ docker Engine API創建的容器）。節點的狀態只影響service

1. 查看redis容器分布的節點

[root@node1 ~]# docker service ps redis
ID                  NAME                IMAGE               NODE                DESIRED STATE       CURRENT STATE           ERROR               PORTS
2au9etgoryzy        redis.1             redis:3.0.7         node1               Running             Running 2 hours ago                         
daxio9w01x6f         \_ redis.1         redis:3.0.6         node2               Shutdown            Shutdown 2 hours ago                        
t5na1flecwgb        redis.2             redis:3.0.7         node1               Running             Running 2 hours ago                         
ny2ia69mibek         \_ redis.2         redis:3.0.6         node2               Shutdown            Shutdown 2 hours ago                        
355xlpbugpt2        redis.3             redis:3.0.7         node1               Running             Running 2 hours ago                         
305huk42qp07         \_ redis.3         redis:3.0.6         node1               Shutdown            Shutdown 10 hours ago                       
[root@node1 ~]# 

2. 清空node1節點的任務

[root@node1 ~]# docker node update --availability drain node1 
node1

3. 查看此時任務分配的節點

[root@node1 ~]# docker service ps redis
ID                  NAME                IMAGE               NODE                DESIRED STATE       CURRENT STATE            ERROR               PORTS
3r2nu9exguqf        redis.1             redis:3.0.7         node2               Running             Starting 2 seconds ago                       
2au9etgoryzy         \_ redis.1         redis:3.0.7         node1               Shutdown            Shutdown 2 seconds ago                       
daxio9w01x6f         \_ redis.1         redis:3.0.6         node2               Shutdown            Shutdown 2 hours ago                         
3ie4hycd9m55        redis.2             redis:3.0.7         node2               Running             Starting 1 second ago                        
t5na1flecwgb         \_ redis.2         redis:3.0.7         node1               Shutdown            Shutdown 2 seconds ago                       
ny2ia69mibek         \_ redis.2         redis:3.0.6         node2               Shutdown            Shutdown 2 hours ago                         
ihnnj7k74aud        redis.3             redis:3.0.7         node2               Running             Starting 1 second ago                        
355xlpbugpt2         \_ redis.3         redis:3.0.7         node1               Shutdown            Shutdown 2 seconds ago                       
305huk42qp07         \_ redis.3         redis:3.0.6         node1               Shutdown            Shutdown 10 hours ago                        

可以看到此時任務都分配到了node2節點

4. 檢查節點的可用性

[root@node1 ~]# docker node inspect --pretty node1
ID:			28t3r12oxo2k9derz8i7yxw7p
Hostname:              	node1
Joined at:             	2019-06-08 12:20:34.266379324 +0000 utc
Status:
 State:			Ready
 Availability:         	Drain
 Address:		192.168.229.128
...

5. 啟用被清空的節點

[root@node1 ~]# docker node update --availability active node1
node1

[root@node1 ~]# docker node inspect --pretty node1
ID:			28t3r12oxo2k9derz8i7yxw7p
Hostname:              	node1
Joined at:             	2019-06-08 12:20:34.266379324 +0000 utc
Status:
 State:			Ready
 Availability:         	Active
 Address:		192.168.229.128

當節點的狀態變為Active時，可以接受新的任務

• 在服務更新期間進行擴展
• 在滾動更新期間
• 當您設置另一個節點以耗盡可用性時
• 當另一個活動節點上的任務失敗時

參考
https://my.oschina.net/u/915811/blog/1593856
https://docs.docker.com/engine/swarm/swarm-tutorial/drain-node/