感覺昨天講了一堆廢話，沒真正實作的話我自己是看不懂拉，今天將應用Docker官方的範例來做Swarm的使用並做擴展。

實作

事前配置

首先先將官方實例clone下來再bulid就好

git clone https://github.com/dockersamples/node-bulletin-board
cd node-bulletin-board/bulletin-board-app
docker build --tag bulletinboard:1.0 .

接下來再建立bb-stack.yaml，包含以下的內容(此檔案就如同compose-file)

version: '3.7'

services:
  bb-app:
    image: bulletinboard:1.0
    ports:
      - "8000:8080"

在使用之前要先確認Swarm功能是有運行的，如果沒有就初始Swarm，Docker就會自動建立Swarm manager能先體驗一下功能

docker swarm init

建立Swarm service

一切就緒之後就可以deploy來使用我們的stack

$ docker stack deploy -c bb-stack.yaml mystack
Creating network mystack_default
Creating service mystack_bb-app

部屬好我們的stack之後可以使用service命令來觀察我們建立的service，可以看到service ID還有一些詳細資訊

$ docker service ls
ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
27g4pcawle5o        mystack_bb-app      replicated          1/1                 bulletinboard:1.0   *:8000->8080/tcp

也可以觀察node這昨天提過

再來是做擴展的功能，擴展也是使用service指令，格式如下

docker service scale <SERVICE-ID>=<NUMBER-OF-TASKS>

再搭配我們剛剛觀察到的service ID建立擴展十個，就會增加十個task

$ docker service scale 27g4pcawle5o=1027g4pcawle5o scaled to 10
27g4pcawle5o scaled to 10
overall progress: 10 out of 10 tasks
1/10: running   [==================================================>]
2/10: running   [==================================================>]
3/10: running   [==================================================>]
4/10: running   [==================================================>]
5/10: running   [==================================================>]
6/10: running   [==================================================>]
7/10: running   [==================================================>]
8/10: running   [==================================================>]
9/10: running   [==================================================>]
10/10: running   [==================================================>]
verify: Service converged

再回去查看我們的service，REPLICAS就變成了十個

$ docker service ls
ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
27g4pcawle5o        mystack_bb-app      replicated          10/10               bulletinboard:1.0   *:8000->8080/tcp

也能透過ps來查看對應service的資訊

$ docker service ps 27g4pcawle5o
ID                  NAME                IMAGE               NODE                DESIRED STATE       CURRENT STATE            ERROR               PORTS
qphzkfmn5c7t        mystack_bb-app.1    bulletinboard:1.0   docker-desktop      Running             Running 26 minutes ago
8qna1q65sdsb        mystack_bb-app.2    bulletinboard:1.0   docker-desktop      Running             Running 5 minutes ago
xuqussywhffl        mystack_bb-app.3    bulletinboard:1.0   docker-desktop      Running             Running 5 minutes ago
ex0dg88uu5gy        mystack_bb-app.4    bulletinboard:1.0   docker-desktop      Running             Running 5 minutes ago
2h8prgkgpolm        mystack_bb-app.5    bulletinboard:1.0   docker-desktop      Running             Running 5 minutes ago
7y6wtubgi9om        mystack_bb-app.6    bulletinboard:1.0   docker-desktop      Running             Running 5 minutes ago
6vuncarl1is4        mystack_bb-app.7    bulletinboard:1.0   docker-desktop      Running             Running 5 minutes ago
yjroyvbvkhke        mystack_bb-app.8    bulletinboard:1.0   docker-desktop      Running             Running 5 minutes ago
yru1cx4rbu7z        mystack_bb-app.9    bulletinboard:1.0   docker-desktop      Running             Running 5 minutes ago
zfutz1757xpf        mystack_bb-app.10   bulletinboard:1.0   docker-desktop      Running             Running 5 minutes ago

這十個擴展就能提供給Swarm自動做負載平衡

刪除Swarm service

刪除的語法則是使用docker service rm <stack-name>就好

$ docker service rm 27g4pcawle5o
27g4pcawle5o

總結:

看了兩天終於看懂manager跟worker到底是在說甚麼了，不過由於時間已經太晚就只稍微講一下，manager跟worker都是各自的虛擬機或是實體機拉，所以我每次Swarm join都在manager自然會報錯，真是搞笑。好啦不過我們今天已經將Swarm基本功能玩過了。接下來來研究怎麼部署我們的container image到cloud吧，是跟Docker hub有關嗎?

參考文獻:
docker官方文件