[ 문제 발생 ]

* eth0 과 docker0 의 mtu가 다른 상황입니다. MTU가 다를때는 옵션을 줘서 동일 값으로 셋팅합니다.

[root@localhost]# ip link
1: lo:  mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0:  mtu 1450 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
    link/ether fa:16:3e:0a:b2:dc brd ff:ff:ff:ff:ff:ff
3: docker0:  mtu 1500 qdisc noqueue state DOWN mode DEFAULT 
    link/ether 02:42:86:b8:b7:01 brd ff:ff:ff:ff:ff:ff

* docker MTU 기본값을 변경 합니다.

[ centos7 ]
[root@localhost]# vi /lib/systemd/system/docker.service

[Unit]
Description=Docker Application Container Engine
Documentation=http://docs.docker.com
After=network.target rhel-push-plugin.socket registries.service
Wants=docker-storage-setup.service
Requires=docker-cleanup.timer

[Service]
Type=notify
NotifyAccess=all
EnvironmentFile=-/run/containers/registries.conf
EnvironmentFile=-/etc/sysconfig/docker
EnvironmentFile=-/etc/sysconfig/docker-storage
EnvironmentFile=-/etc/sysconfig/docker-network
Environment=GOTRACEBACK=crash
Environment=DOCKER_HTTP_HOST_COMPAT=1
Environment=PATH=/usr/libexec/docker:/usr/bin:/usr/sbin
ExecStart=/usr/bin/dockerd-current \
          --add-runtime docker-runc=/usr/libexec/docker/docker-runc-current \
          --default-runtime=docker-runc \
          --exec-opt native.cgroupdriver=systemd \
          --userland-proxy-path=/usr/libexec/docker/docker-proxy-current \
          --seccomp-profile=/etc/docker/seccomp.json \
          --mtu 1450 \
          $OPTIONS \
          $DOCKER_STORAGE_OPTIONS \
          $DOCKER_NETWORK_OPTIONS \
          $ADD_REGISTRY \
          $BLOCK_REGISTRY \
          $INSECURE_REGISTRY \
          $REGISTRIES
ExecReload=/bin/kill -s HUP $MAINPID
LimitNOFILE=1048576
LimitNPROC=1048576
LimitCORE=infinity
TimeoutStartSec=0
Restart=on-abnormal
MountFlags=slave
KillMode=process

[Install]
WantedBy=multi-user.target


[ ubuntu 16.04]
[root@localhost]# vi /lib/systemd/system/docker.service

[Unit]
Description=Docker Application Container Engine
Documentation=https://docs.docker.com
After=network-online.target docker.socket firewalld.service
Wants=network-online.target
Requires=docker.socket

[Service]
Type=notify
# the default is not to use systemd for cgroups because the delegate issues still
# exists and systemd currently does not support the cgroup feature set required
# for containers run by docker
ExecStart=/usr/bin/dockerd -H fd:// --mtu 1450
ExecReload=/bin/kill -s HUP $MAINPID
LimitNOFILE=1048576
# Having non-zero Limit*s causes performance problems due to accounting overhead
# in the kernel. We recommend using cgroups to do container-local accounting.
LimitNPROC=infinity
LimitCORE=infinity
# Uncomment TasksMax if your systemd version supports it.
# Only systemd 226 and above support this version.
TasksMax=infinity
TimeoutStartSec=0
# set delegate yes so that systemd does not reset the cgroups of docker containers
Delegate=yes
# kill only the docker process, not all processes in the cgroup
KillMode=process
# restart the docker process if it exits prematurely
Restart=on-failure
StartLimitBurst=3
StartLimitInterval=60s

[Install]
WantedBy=multi-user.target
~                              


[root@skhkil 04:41:22:/lib/systemd/system]# systemctl daemon-reload 
[root@skhkil 04:41:30:/lib/systemd/system]# service docker restart
Redirecting to /bin/systemctl restart docker.service

* centos7 ,ubuntu16.04 에서 MTU 값을 서버와 동일하게 셋팅하고, 재접속 또는 docker os 마운트해서 확인하면 mtu 변경 확인이 가능 합니다.

[root@localhost]# ip link
1: lo:  mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0:  mtu 1450 qdisc pfifo_fast state UP mode DEFAULT qlen 1000
    link/ether fa:16:3e:0a:b2:dc brd ff:ff:ff:ff:ff:ff
3: docker0:  mtu 1450 qdisc noqueue state UP mode DEFAULT 
    link/ether 02:42:86:b8:b7:01 brd ff:ff:ff:ff:ff:ff
107: vethf134985@if106:  mtu 1450 qdisc noqueue master docker0 state UP mode DEFAULT 
    link/ether 42:82:96:46:44:b4 brd ff:ff:ff:ff:ff:ff link-netnsid 0