Docker Overlay网络的MTU
Docker Daemon生产环境配置提到了MTU设置，但是这只是针对于名为bridge的docker bridge network，对于overlay network是无效的。
如果docker host machine的网卡MTU为1500，则不需要此步骤
设置ingress和docker_gwbridge的MTU
以下步骤得在swarm init或join之前做
假设你有三个机器，manager、worker-1、worker-2，准备搞一个Docker swarm集群
1) [manager] docker swarm init
2) [manager] 获得docker_gwbridge的参数，注意Subnet
$ docker network inspect docker_gwbridge
[
{
"Name": "docker_gwbridge",
...
"IPAM": {
...
"Config": [
{
"Subnet": "172.18.0.0/16",
...
}
]
},
...
}
]3) [manager] docker swarm leave --force
4) [manager] 停掉docker sudo systemctl stop docker.service
5) [manager] 删掉虚拟网卡docker_gwbridge
$ sudo ip link set docker_gwbridge down $ sudo ip link del dev docker_gwbridge
6) [manager] 启动docker sudo systemctl start docker.service
7) [manager] 重建docker_gwbridge，
记得设置之前得到的Subnet参数和正确的MTU值
$ docker network rm docker_gwbridge $ docker network create \ --subnet 172.18.0.0/16 \ --opt com.docker.network.bridge.name=docker_gwbridge \ --opt com.docker.network.bridge.enable_icc=false \ --opt com.docker.network.bridge.enable_ip_masquerade=true \ --opt com.docker.network.driver.mtu=1450 \ docker_gwbridge
再到worker-1和worker-2上执行相同的命令。
8) [manager] docker swarm init
9) [manager] 先观察ingress network的参数，注意Subnet和Gateway：
$ docker network inspect ingress
[
{
"Name": "ingress",
...
"IPAM": {
...
"Config": [
{
"Subnet": "10.255.0.0/16",
"Gateway": "10.255.0.1"
}
]
},
...
}
]10) [manager] 删除ingress network，docker network rm ingress。
11) [manager] 重新创建ingress network，记得填写之前得到的Subnet和Gateway，以及正确的MTU值：
$ docker network create \ --driver overlay \ --ingress \ --subnet=10.255.0.0/16 \ --gateway=10.255.0.1 \ --opt com.docker.network.driver.mtu=1450 \ ingress
12) [worker-1] [worker-2] join docker swarm join ...
注意：新机器在join到swarm之前，得先执行第7步
验证：
1) 启动一个swarm service，docker service create -td --name busybox busybox
2) 观察虚拟网卡
发现MTU都是1450：
$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
link/ether fa:16:3e:71:09:f5 brd ff:ff:ff:ff:ff:ff
3: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UP mode DEFAULT group default
link/ether 02:42:6b:de:95:71 brd ff:ff:ff:ff:ff:ff
298: docker_gwbridge: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UP mode DEFAULT group default
link/ether 02:42:ae:7b:cd:b4 brd ff:ff:ff:ff:ff:ff
309: veth7e0f9e5@if308: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue master docker_gwbridge state UP mode DEFAULT group default
link/ether 16:ca:8f:c7:d3:7f brd ff:ff:ff:ff:ff:ff link-netnsid 1
311: vethcb94fec@if310: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue master docker0 state UP mode DEFAULT group default
link/ether 9a:aa:de:7b:4f:d4 brd ff:ff:ff:ff:ff:ff link-netnsid 23) 观察容器内网卡
网卡MTU也是1450：
$ docker exec b.1.pdsdgghzyy5rhqkk5et59qa3o ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
310: eth0@if311: <BROADCAST,MULTICAST,UP,LOWER_UP,M-DOWN> mtu 1450 qdisc noqueue
link/ether 02:42:ac:11:00:02 brd ff:ff:ff:ff:ff:ff自建overlay network的MTU
方法一：在docker compose file设置
...
networks:
my-overlay:
driver: bridge
driver_opts:
com.docker.network.driver.mtu: 1450不过这样不好，因为这样就把docker compose file的内容和生产环境绑定了，换了个环境这个MTU值未必合适。
方法二：外部创建时设置
docker network create \ -d overlay \ --opt com.docker.network.driver.mtu=1450 \ --attachable \ my-overlay
用法：
在docker compose file里这样用：
... networks: app-net: external: true name: my-overlaydocker run --network my-overlay ...docker service create --network my-overlay ...