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Docker Swarm mode 指令教學 | docker service
之前一直都討論Image 的打包形式，現在聊聊部署上線時的一些指令。
Docker Service
swarm mode 主要通過"docker service" 指令去產生一堆可以在不同節點上運行的container。為了更加形象地講，我把container稱為Image的分身。
docker service create跟docker container run的感覺很像，兩者都可以指定image
# swarm mode
$ docker swarm init
$ docker service create --name nginx_s nginx
# container mode
$ docker container run -d --name nginx_c nginx
兩者的差別在於docker service 可以指定多少個分身，可以隨時加減數目，而且如果你有多過一台機器，分身就會在不同的機器上遊走。而docker container就是只對本機有操作，也不會散播到其他機器。
# swarm mode
$ docker service create --replicas=2 --name nginx_s nginx
$ docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
uro4rwy6nelh nginx_s replicated 2/2 nginx:latest
$ docker service update --replicas=5 nginx_s
$ docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
uro4rwy6nelh nginx_s replicated 5/5 nginx:latest
# container mode
$ docker container run -d --name nginx_c1 nginx
$ docker container run -d --name nginx_c2 nginx
$ docker container run -d --name nginx_c3 nginx
$ docker container run -d --name nginx_c4 nginx
$ docker container run -d --name nginx_c5 nginx
$ docker container ls
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
c45771f06612 nginx "/docker-entrypoint.…" 7 seconds ago Up 6 seconds 80/tcp nginx_c5
a587a718da3a nginx "/docker-entrypoint.…" 9 seconds ago Up 9 seconds 80/tcp nginx_c4
079f206f8645 nginx "/docker-entrypoint.…" 9 seconds ago Up 9 seconds 80/tcp nginx_c3
e10dc525fd22 nginx "/docker-entrypoint.…" 10 seconds ago Up 9 seconds 80/tcp nginx_c2
dcaa2b4bb3de nginx "/docker-entrypoint.…" 10 seconds ago Up 9 seconds 80/tcp nginx_c1
在建立網段時也差不多，service需要的是overlay network，而container用一般network就可以。
# swarm mode
$ docker network create --driver overlay nginx_s_gateway
$ docker service update --network-add name=nginx_s_gateway,alias=gateway nginx_s
$ docker service ps nginx_s
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS
fxqtheyvr914 nginx_s.1 nginx:latest dockertest Running Running 33 seconds ago
u0pvj1leoizw \_ nginx_s.1 nginx:latest dockertest Shutdown Shutdown 33 seconds ago
q7arumjlxduv nginx_s.2 nginx:latest dockertest Running Running 36 seconds ago
kurlwqfmopbg \_ nginx_s.2 nginx:latest dockertest Shutdown Shutdown 37 seconds ago
zd0zlkhxafv0 nginx_s.3 nginx:latest dockertest Running Running 40 seconds ago
3kapr00fs6pt \_ nginx_s.3 nginx:latest dockertest Shutdown Shutdown 40 seconds ago
5o4afd3whygo nginx_s.4 nginx:latest dockertest Running Running 35 seconds ago
oxocropolbo8 \_ nginx_s.4 nginx:latest dockertest Shutdown Shutdown 35 seconds ago
x5y94jf3ok51 nginx_s.5 nginx:latest dockertest Running Running 38 seconds ago
cgld3au0w1i9 \_ nginx_s.5 nginx:latest dockertest Shutdown Shutdown 39 seconds ago
# container mode
$ docker network create nginx_c_gateway
$ docker network connect --alias gateway nginx_c_gateway nginx_c1
$ docker network connect --alias gateway nginx_c_gateway nginx_c2
$ docker network connect --alias gateway nginx_c_gateway nginx_c3
$ docker network connect --alias gateway nginx_c_gateway nginx_c4
$ docker network connect --alias gateway nginx_c_gateway nginx_c5
不過比較大的差異是service會停了原有的分身，重開新的分身去加入網段。所以上面的docker service ps nginx_s執行結果，就有一半是停掉的。
類似地，docker service也不能單獨地停掉分身，頂多只能調整--replicas=NUMBER，來控制分身數量。而單機則可以經過docker container stop來暫停分身。
