4.9 Docker Overlay網絡和etcd實現多機容器通訊

實現多機容器的通訊，首先須要保證容器的ip在多臺虛擬機中都是惟一的。以上圖爲例，在192.168.205.10中新建容器，就不能再出現容器的ip爲172.17.0.3了，由於這個ip已經在192.168.205.10中存在了。

etcd安裝

爲了保證容器在多機中的ip惟一，能夠使用etcd，etcd是一個開源的、分佈式的鍵值對數據存儲系統

https://coreos.com/etcd/

在docker-node1上安裝etcd

wget https://github.com/coreos/etcd/releases/download/v3.0.12/etcd-v3.0.12-linux-amd64.tar.gz
tar zxvf etcd-v3.0.12-linux-amd64.tar.gz
cd etcd-v3.0.12-linux-amd64
nohup ./etcd --name docker-node1 --initial-advertise-peer-urls http://192.168.205.10:2380 
--listen-peer-urls http://192.168.205.10:2380 
--listen-client-urls http://192.168.205.10:2379,http://127.0.0.1:2379 
--advertise-client-urls http://192.168.205.10:2379 
--initial-cluster-token etcd-cluster 
--initial-cluster docker-node1=http://192.168.205.10:2380,docker-node2=http://192.168.205.11:2380 
--initial-cluster-state new &

在docker-node2上安裝etcd

wget https://github.com/coreos/etcd/releases/download/v3.0.12/etcd-v3.0.12-linux-amd64.tar.gz
tar zxvf etcd-v3.0.12-linux-amd64.tar.gz
cd etcd-v3.0.12-linux-amd64/
nohup ./etcd --name docker-node2 --initial-advertise-peer-urls http://192.168.205.11:2380 
--listen-peer-urls http://192.168.205.11:2380 
--listen-client-urls http://192.168.205.11:2379,http://127.0.0.1:2379 
--advertise-client-urls http://192.168.205.11:2379 
--initial-cluster-token etcd-cluster 
--initial-cluster docker-node1=http://192.168.205.10:2380,docker-node2=http://192.168.205.11:2380 
--initial-cluster-state new &

在docker-node1或docker-node2任一主機上檢查cluster運行狀態

./etcdctl cluster-health
member 21eca106efe4caee is healthy: got healthy result from http://192.168.205.10:2379
member 8614974c83d1cc6d is healthy: got healthy result from http://192.168.205.11:2379
cluster is healthy

docker重啓

使用 systemctl stop docker 命令，關閉docker服務後再使用以下方式重啓
docker-node1

sudo /usr/bin/dockerd -H tcp://0.0.0.0:2375 -H unix:///var/run/docker.sock --cluster-store=etcd://192.168.205.10:2379 --cluster-advertise=192.168.205.10:2375 &

docker-node2

sudo /usr/bin/dockerd -H tcp://0.0.0.0:2375 -H unix:///var/run/docker.sock --cluster-store=etcd://192.168.205.11:2379 --cluster-advertise=192.168.205.11:2375 &

建立overlay network

在docker-node1上建立一個demo的overlay network

docker network create -d overlay demo

docker-node1，能夠看到demo的DRIVER是overlay，SCOPE是global

[vagrant@docker-node1 etcd-v3.0.12-linux-amd64]$ docker network ls
NETWORK ID NAME DRIVER SCOPE
9bacf5670fa1 bridge bridge local
5a8cd36174a1 demo overlay global
efb6975c8935 host host local
4213425c5293 my-bridge bridge local
3fa0f2e1a00b none null local

而後在docker-node2上發現會同步建立

[vagrant@docker-node2 etcd-v3.0.12-linux-amd64]$ docker network ls
NETWORK ID NAME DRIVER SCOPE
1c79331058ff bridge bridge local
5a8cd36174a1 demo overlay global
148fe990ddc5 host host local
452bd665cf13 none null local

經過查看etcd的key-value，發現docker network inspect demo的內容與key-value中的內容是同樣的，也就是所謂的分佈式網絡

[
    {
        "Name": "demo",
        "Id": "5a8cd36174a1b37f9146aaa99de33ff20bfa8df472e07412e36048a39fe9a0e9",
        "Created": "2018-07-03T09:21:08.95776633Z",
        "Scope": "global",
        "Driver": "overlay",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "10.0.0.0/24",
                    "Gateway": "10.0.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {},
        "Options": {},
        "Labels": {}
    }
]

測試多機通訊效果

在docker-node1上

docker run -d --name test1 --network demo busybox /bin/sh -c "while true;do sleep 3600;done"

在docker-node2上若是重複執行上述命令，就會報以下錯誤了，從另外一方面也說明了etcd在發揮做用

docker: Error response from daemon: Conflict. The container name "/test1" is already in use by container "14d690ada81a4510eb5dd24286d061064e8131f549dcb5320f5b5b441cc49c40". You have to remove (or rename) that container to be able to reuse that name.

能夠改成

docker run -d --name test2 --network demo busybox /bin/sh -c "while true;do sleep 3600;done"

此時查看一下docker-node1與docker-node2分別對應的test1與test2容器的網絡

docker network inspect demo
{
 "Containers": {
 "a9fa503852b26267d13b67067ba6c119eebcf0677f8365483b3b798dcab616a5": {
 "Name": "test1",
 "EndpointID": "3869243fcfb6a975fadf64dc31533161d2922137b18af0c3ee78c02f82b84def",
 "MacAddress": "",
 "IPv4Address": "10.0.0.2/24",
 "IPv6Address": ""
 },
 "ep-8f8e30e36867c5b906bc84438049b2911660057fe031536a97efcf01d7d98699": {
 "Name": "test2",
 "EndpointID": "8f8e30e36867c5b906bc84438049b2911660057fe031536a97efcf01d7d98699",
 "MacAddress": "",
 "IPv4Address": "10.0.0.3/24",
 "IPv6Address": ""
 }
 }
}

而後在test1上ping位於docker-node2上的test2容器是能夠ping通的

docker exec test1 ping 10.0.0.3

在test2上ping位於docker-node1上的test1容器也是能夠ping通的

docker exec test2 ping 10.0.0.2

成功實現了多機容器通訊的效果