Docker daemon flags ignored

Recommended Way Docker 17.xx +

There are a number of ways to configure the daemon flags and environment variables for your Docker daemon. The recommended way is to use the platform-independent daemon.json file, which is located in /etc/docker/ on Linux by default.

So, for configuring insecure registries, do the following:

1. Set the following flag in the /etc/docker/daemon.json file:

   {
       "insecure-registries": ["mydocker-registry.net:5000"]
   }
   

2. Restart Docker

    $ sudo systemctl restart docker
   

Easier each time!

---

Previously Recommended Way with Docker 1.12

According to docker documentation, The recommended way to configure the daemon flags and environment variables for your Docker daemon is to use a systemd drop-in file.

So, for this specific case, do the following:

1. Create a file called /etc/systemd/system/docker.service.d/private-registry.conf with the following content:

   If not exists, create directory /etc/systemd/system/docker.service.d

   [Service]
   ExecStart=
   ExecStart=/usr/bin/dockerd --insecure-registry mydocker-registry.net:5000
   

2. Flush changes:

   $ sudo systemctl daemon-reload
   

3. Restart Docker:

    $ sudo systemctl restart docker
   

Voila!

---

Not recommended way

Edit file /lib/systemd/system/docker.service

...
[Service]
ExecStart=/usr/bin/docker -d -H fd:// $DOCKER_OPTS
...
EnvironmentFile=-/etc/default/docker
...

Then execute

systemctl daemon-reload
systemctl restart docker

Verify that /etc/default/docker is loaded

ps auxwww | grep docker
root      4989  0.8  0.1 265540 16608 ?        Ssl  10:37   0:00 /usr/bin/docker -d -H fd:// --insecure-registry 

That's it.

Things seem to have changed in Ubuntu 16.04 using docker 1.12.x. Based on the updated documentation

Add DOCKER_OPTS="-g /mnt/somewhere/else/docker/ --storage-driver=overlay2" to /etc/default/docker

Edit file /lib/systemd/system/docker.service

...
[Service]
ExecStart=/usr/bin/dockerd -H fd:// $DOCKER_OPTS
...
EnvironmentFile=-/etc/default/docker
...

Then execute:

sudo systemctl daemon-reload
sudo systemctl restart docker