Customizing docker

The Docker systemd unit can be customized by overriding the unit that ships with the default CoreOS settings. Common use-cases for doing this are covered below.

Enable the remote API on a new socket (Test on Centos .latest docker 1.12)

新版的 Docker 使用 /etc/docker/daemon.json（Linux）或者 %programdata%\docker\config\daemon.json（Windows）来配置 Daemon。

请在该配置文件中加入（没有该文件的话，请先建一个）：

{

  "hosts": ["unix:///var/run/docker.sock", "tcp://0.0.0.0:8400", "tcp://0.0.0.0:2375"],
  "registry-mirrors": ["https://docker.mirrors.ustc.edu.cn"]

}

Enable the remote API on a new socket

Create a file called /etc/systemd/system/docker-tcp.socket to make Docker available on a TCP socket on port 2375.

[Unit]

Description=Docker Socket for the API

[Socket]

ListenStream=2375

BindIPv6Only=both

Service=docker.service

[Install]

WantedBy=sockets.target

Then enable this new socket:

systemctl enable docker-tcp.socket

systemctl stop docker

systemctl start docker-tcp.socket

systemctl start docker

Test that it’s working:

docker -H tcp://127.0.0.1:2375 ps

Cloud-config

To enable the remote API on every CoreOS machine in a cluster, use cloud-config. We need to provide the new socket file and Docker’s socket activation support will automatically start using the socket:

#cloud-config

coreos:

  units:

    - name: docker-tcp.socket

      command: start

      enable: true

      content: |

        [Unit]

        Description=Docker Socket for the API

        [Socket]

        ListenStream=2375

        BindIPv6Only=both

        Service=docker.service

        [Install]

        WantedBy=sockets.target

To keep access to the port local, replace the ListenStream configuration above with:

        [Socket]

        ListenStream=127.0.0.1:2375

Enable the remote API with TLS authentication

Docker TLS configuration consists of three parts: keys creation, configuring new systemd socket unit and systemd drop-in configuration.

TLS keys creation

Please follow the instruction to know how to create self-signed certificates and private keys. Then copy with following files into /etc/docker CoreOS’ directory and fix their permissions:

scp ~/cfssl/{server.pem,server-key.pem,ca.pem} coreos.example.com:

ssh core@coreos.example.com

sudo mv {server.pem,server-key.pem,ca.pem} /etc/docker/

sudo chown root:root /etc/docker/{server-key.pem,server.pem,ca.pem}

sudo chmod 0600 /etc/docker/server-key.pem

On your local host copy certificates into ~/.docker:

mkdir ~/.docker

chmod 700 ~/.docker

cd ~/.docker

cp -p ~/cfssl/ca.pem ca.pem

cp -p ~/cfssl/client.pem cert.pem

cp -p ~/cfssl/client-key.pem key.pem

Enable the secure remote API on a new socket

NOTE: For CoreOS releases older than 949.0.0 you must follow this guide.

Create a file called /etc/systemd/system/docker-tls-tcp.socket to make Docker available on a secured TCP socket on port 2376.

[Unit]

Description=Docker Secured Socket for the API

[Socket]

ListenStream=2376

BindIPv6Only=both

Service=docker.service

[Install]

WantedBy=sockets.target

Then enable this new socket:

systemctl enable docker-tls-tcp.socket

systemctl stop docker

systemctl start docker-tls-tcp.socket

Drop-in configuration

Create /etc/systemd/system/docker.service.d/10-tls-verify.conf drop-in for systemd Docker service:

[Service]

Environment="DOCKER_OPTS=--tlsverify --tlscacert=/etc/docker/ca.pem --tlscert=/etc/docker/server.pem --tlskey=/etc/docker/server-key.pem"

Reload systemd config files and restart docker service:

sudo systemctl daemon-reload

sudo systemctl restart docker.service

Now you can access your Docker’s API through TLS secured connection:

docker --tlsverify -H tcp://server:2376 images

# or

docker --tlsverify -H tcp://server.example.com:2376 images

If you’ve experienceed problems connection to remote Docker API using TLS connection, you can debug it with curl:

curl -v --cacert ~/.docker/ca.pem --cert ~/.docker/cert.pem --key ~/.docker/key.pem https://server:2376

Or on your CoreOS host:

journalctl -f -u docker.service

In addition you can export environment variables and use docker client without additional options:

export DOCKER_HOST=tcp://server.example.com:2376 DOCKER_TLS_VERIFY=1

docker images

Cloud-config

Cloud-config for Docker TLS authentication will look like:

#cloud-config

write_files:

    - path: /etc/docker/ca.pem

      permissions: 0644

      content: |

        -----BEGIN CERTIFICATE-----

        MIIFNDCCAx6gAwIBAgIBATALBgkqhkiG9w0BAQswLTEMMAoGA1UEBhMDVVNBMRAw

        DgYDVQQKEwdldGNkLWNhMQswCQYDVQQLEwJDQTAeFw0xNTA5MDIxMDExMDhaFw0y

        NTA5MDIxMDExMThaMC0xDDAKBgNVBAYTA1VTQTEQMA4GA1UEChMHZXRjZC1jYTEL

        ... ... ...

    - path: /etc/docker/server.pem

      permissions: 0644

      content: |

        -----BEGIN CERTIFICATE-----

        MIIFajCCA1SgAwIBAgIBBTALBgkqhkiG9w0BAQswLTEMMAoGA1UEBhMDVVNBMRAw

        DgYDVQQKEwdldGNkLWNhMQswCQYDVQQLEwJDQTAeFw0xNTA5MDIxMDM3MDFaFw0y

        NTA5MDIxMDM3MDNaMEQxDDAKBgNVBAYTA1VTQTEQMA4GA1UEChMHZXRjZC1jYTEQ

        ... ... ...

    - path: /etc/docker/server-key.pem

      permissions: 0600

      content: |

        -----BEGIN RSA PRIVATE KEY-----

        MIIJKAIBAAKCAgEA23Q4yELhNEywScrHl6+MUtbonCu59LIjpxDMAGxAHvWhWpEY

        P5vfas8KgxxNyR+U8VpIjEXvwnhwCx/CSCJc3/VtU9v011Ir0WtTrNDocb90fIr3

        YeRWq744UJpBeDHPV9opf8xFE7F74zWeTVMwtiMPKcQDzZ7XoNyJMxg1wmiMbdCj

        ... ... ...

coreos:

  units:

    - name: docker-tls-tcp.socket

      command: start

      enable: true

      content: |

        [Unit]

        Description=Docker Secured Socket for the API

        [Socket]

        ListenStream=2376

        BindIPv6Only=both

        Service=docker.service

        [Install]

        WantedBy=sockets.target

    - name: docker.service

      drop-ins:

        - name: 10-tls-verify.conf

          content: |

            [Service]

            Environment="DOCKER_OPTS=--tlsverify --tlscacert=/etc/docker/ca.pem --tlscert=/etc/docker/server.pem --tlskey=/etc/docker/server-key.pem"

Use attached storage for Docker images

Docker containers can be very large and debugging a build process makes it easy to accumulate hundreds of containers. It’s advantageous to use attached storage to expand your capacity for container images. Check out the guide to mounting storage to your CoreOS machine for an example of how to bind mount storage into /var/lib/docker.

Enabling the Docker debug flag

First, copy the existing unit from the read-only file system into the read/write file system, so we can edit it:

cp /usr/lib/systemd/system/docker.service /etc/systemd/system/

Edit the ExecStart line to add the -D flag:

ExecStart=/usr/bin/docker -d -s=btrfs -r=false -H fd:// -D

Now lets tell systemd about the new unit and restart Docker:

systemctl daemon-reload

systemctl restart docker

To test our debugging stream, run a Docker command and then read the systemd journal, which should contain the output:

docker ps

journalctl -u docker

Cloud-config

If you need to modify a flag across many machines, you can provide the new unit with cloud-config:

#cloud-config

coreos:

  units:

    - name: docker.service

      command: restart

      content: |

        [Unit]

        Description=Docker Application Container Engine

        Documentation=http://docs.docker.io

        After=network.target

        [Service]

        ExecStartPre=/bin/mount --make-rprivate /

        # Run docker but don't have docker automatically restart

        # containers. This is a job for systemd and unit files.

        ExecStart=/usr/bin/docker -d -s=btrfs -r=false -H fd:// -D

        [Install]

        WantedBy=multi-user.target

Use an HTTP proxy

If you’re operating in a locked down networking environment, you can specify an HTTP proxy for Docker to use via an environment variable. First, create a directory for drop-in configuration for Docker:

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

Now, create a file called /etc/systemd/system/docker.service.d/http-proxy.conf that adds the environment variable:

[Service]

Environment="HTTP_PROXY=http://proxy.example.com:8080"

To apply the change, reload the unit and restart Docker:

systemctl daemon-reload

systemctl restart docker

Cloud-config

The easiest way to use this proxy on all of your machines is via cloud-config:

#cloud-config

coreos:

  units:

    - name: docker.service

      drop-ins:

        - name: 20-http-proxy.conf

          content: |

            [Service]

            Environment="HTTP_PROXY=http://proxy.example.com:8080"

      command: restart

Increase ulimits

If you need to increase certain ulimits that are too low for your application by default, like memlock, you will need to modify the Docker service to increase the limit. First, create a directory for drop-in configuration for Docker:

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

Now, create a file called /etc/systemd/system/docker.service.d/increase-ulimit.conf that adds increased limit:

[Service]

LimitMEMLOCK=infinity

To apply the change, reload the unit and restart Docker:

systemctl daemon-reload

systemctl restart docker

Cloud-config

The easiest way to use these new ulimits on all of your machines is via cloud-config:

#cloud-config

coreos:

  units:

    - name: docker.service

      drop-ins:

        - name: 30-increase-ulimit.conf

          content: |

            [Service]

            LimitMEMLOCK=infinity

      command: restart

Using a dockercfg file for authentication

A json file .dockercfg can be created in your home directory that holds authentication information for a public or private Docker registry.

Read more about registry authentication.

https://coreos.com/os/docs/latest/customizing-docker.html