Docker: /etc/default/docker or /etc/sysconfig/docker does not work anymore under systemd?

If you question why all of the sudden your OPTIONS under /etc/default/docker or /etc/sysconfig/docker no longer work, I can assure you that you are not alone!

Let's put it simply, it is due to the /usr/lib/systemd/system/docker.service shipped with newer version of Docker (most probably v1.7 and above).

The file looks like this now =>

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

[Service]
Type=notify
ExecStart=/usr/bin/docker daemon -H fd://
MountFlags=slave<
LimitNOFILE=1048576
LimitNPROC=1048576
LimitCORE=infinity

[Install]
WantedBy=multi-user.target

 You can see clearly that it no longer contains any environment variable for you to customize stuff.

To fix that, we need to create a systemd drop-in file for docker.service.

(1) Create a directory "/etc/systemd/system/docker.service.d" on ALL servers.

mkdir /etc/systemd/system/docker.service.d

(2)  In the directory, create a file - "local.conf" - using your favorite text editor with the following lines:

[Service]
EnvironmentFile=-/etc/sysconfig/docker
EnvironmentFile=-/etc/sysconfig/docker-storage
EnvironmentFile=-/etc/sysconfig/docker-network
ExecStart=
ExecStart=/usr/bin/docker daemon -H fd:// $OPTIONS \
      $DOCKER_STORAGE_OPTIONS \
      $DOCKER_NETWORK_OPTIONS \
      $BLOCK_REGISTRY \
      $INSECURE_REGISTRY

(3) Create or edit the /etc/sysconfig/docker or /etc/sysconfig/docker-storage or /etc/sysconfig/docker-network to specify your customized options.

Eg.
[/etc/sysconfig/docker]
OPTIONS="-H tcp://0.0.0.0:2375 --label nodename=node1.mytestmac.com"

(4) Reload systemd.

systemctl daemon-reload

(5) Verify that docker.service is now aware of its environment files.

systemctl show docker | grep -i env

Eg.
[root@hdp1 ~]# systemctl show docker | grep -i env
EnvironmentFile=/etc/sysconfig/docker (ignore_errors=yes)
EnvironmentFile=/etc/sysconfig/docker-storage (ignore_errors=yes)
EnvironmentFile=/etc/sysconfig/docker-network (ignore_errors=yes)
[root@hdp1 ~]# 

(6) Restart docker.

systemctl restart docker

(7) Verify the changes.

ps -ef | grep docker

Hope that helps to resolve your headaches! :)