Docker's docker container flannel mode multiple network segments across hosts

Problem 1: docker cannot be started

Error prompt:

[root@localhost docker.service.d] # systemctl status docker.service

● docker.service-Docker Application Container Engine

Loaded: error (Reason: Invalid argument)

Drop-In: / usr/lib/systemd/system/docker.service.d

└─ flannel.conf

Active: failed (Result: start-limit) since Fri 2020-01-17 01:18:59 PST; 4min 57s ago

Docs: https://docs.docker.com

Main PID: 9775 (code=exited, status=1/FAILURE)

Jan 17 01:18:56 localhost.localdomain systemd [1]: docker.service failed.

Jan 17 01:18:59 localhost.localdomain systemd [1]: docker.service holdoff time over, scheduling restart.

Jan 17 01:18:59 localhost.localdomain systemd [1]: Stopped Docker Application Container Engine.

Jan 17 01:18:59 localhost.localdomain systemd [1]: start request repeated too quickly for docker.service

Jan 17 01:18:59 localhost.localdomain systemd [1]: Failed to start Docker Application Container Engine.

Jan 17 01:18:59 localhost.localdomain systemd [1]: Unit docker.service entered failed state.

Jan 17 01:18:59 localhost.localdomain systemd [1]: docker.service failed.

Jan 17 01:20:37 localhost.localdomain systemd [1]: docker.service has more than one ExecStart= setting, wh...ing.

Jan 17 01:21:34 localhost.localdomain systemd [1]: docker.service has more than one ExecStart= setting, wh...ing.

Jan 17 01:23:46 localhost.localdomain systemd [1]: docker.service has more than one ExecStart= setting, wh...ing.

Hint: Some lines were ellipsized, use-l to show in full.

Resolve:

Upgrade the kernel:

[root@localhost docker.service.d] # yum update-y

After the upgrade is complete, uninstall the old version and reinstall docker-ce.

[root@localhost docker.service.d] # rpm-qa | grep docker-ce

Docker-ce-19.03.5-3.el7.x86_64

Docker-ce-cli-19.03.5-3.el7.x86_64

[root@localhost docker.service.d] # rpm-e-nodeps docker-ce-19.03.5-3.el7.x86_64

[root@localhost docker.service.d] # rpm-e-nodeps docker-ce-cli-19.03.5-3.el7.x86_64

[root@localhost docker.service.d] # yum install-y docker-ce-*

[root@localhost docker.service.d] # systemctl start docker

[root@localhost docker.service.d] # systemctl status docker

Docker starts normally!

Reflect: can you install flannel first, and then follow docker-ce? will a similar situation occur? To be tested!

Problem 2: docker and flannel start normally, but docker0 cannot get the address pool address.

Resolve:

Modify / usr/lib/systemd/system/docker.service file

[root@localhost docker.service.d] # vim / usr/lib/systemd/system/docker.service

Add the following:

Add $DOCKER_NETWORK_OPTIONS after ExecStart=/usr/bin/dockerd

Add at the end of [server]

EnvironmentFile=/run/flannel/docker

Restart docker

[root@localhost docker.service.d] # systemctl daemon-reload

[root@localhost docker.service.d] # systemctl restart docker.service

[root@localhost docker.service.d] # ifconfig

Docker0 normally acquires the flannel address pool.