dockerd

• CLI

• daemon.json

  • registry-mirrors

  • proxy

  • hosts for socket

  • storage

  • userns-remap

  • logs

  • full sample file

• enable tcp port 2375 for external connection to docker

[!NOTE|label:references:]

• dockerd

CLI

• to verify daemon.json

  $ dockerd --validate --config-file=/etc/docker/daemon.json
  configuration OK
  
  # or
  $ dockerd --debug --validate --config-file /etc/docker/daemon.json
  configuration OK

daemon.json

[!TIP|label:references:]

• Docker daemon configuration overview

  • linux: /etc/docker/daemon.json

  • linux rootless: [[ -n "${XDG_CONFIG_HOME}" ]] && ${XDG_CONFIG_HOME}/docker/daemon.json || ~/.config/docker/daemon.json

  • windows: C:\ProgramData\docker\config\daemon.json

• Protect the Docker daemon socket
• Configure and troubleshoot the Docker daemon
• Set Up Docker with TLS
• How to Configure Docker daemon with a configuration file?
• * Troubleshooting the Docker daemon

registry-mirrors

[!NOTE|label:references:]

• How to change the default docker registry from docker.io to my private registry?
• #11815 Allow configuration of additional registries

$ cat /etc/docker/daemon.json
{
  "registry-mirrors": ["https://artifactory.domain.com"]
}
$ sudo systemctl daemon-reload
$ sudo systemctl restart docker

# equal to `docker pull artifactory.domain.com/docker-local/image:tag`
$ docker pull docker-local/image:tag

# check status
$ docker info | sed -n '/Registry Mirrors:/{p;n;p;}'
 Registry Mirrors:
  https://artifactory.domain.com/

proxy

[!NOTE|label:references:]

• request Docker Engine version 23.0 or later

• Proxy configuration
• control and configure Docker with systemd

{
  "proxies": {
    "http-proxy": "http://proxy.example.com:3128",
    "https-proxy": "https://proxy.example.com:3129",
    "no-proxy": "*.test.example.com,.example.org,127.0.0.0/8"
  }
}

hosts for socket

[!NOTE|label:references:]

• Configuring remote access with daemon.json

{
  "hosts": ["unix:///var/run/docker.sock", "tcp://127.0.0.1:2375"]
}

• or

  {
    "hosts": ["unix:///var/run/docker.sock", "fd://", "tcp://0.0.0.0:2375"]
  }

storage

[!TIP]

• Supported storage drivers per Linux distribution

LINUX DISTRIBUTION	RECOMMENDED STORAGE DRIVERS	ALTERNATIVE DRIVERS
Ubuntu	overlay2	zfs, vfs
Debian	overlay2	vfs
CentOS	overlay2	zfs, vfs
Fedora	overlay2	zfs, vfs
SLES 15	overlay2	vfs
RHEL	overlay2	vfs

• to check current storage driver

  $ docker info | sed -n '/Storage Driver/{p;n;p}'
   Storage Driver: overlay2
    Backing Filesystem: extfs

• data-root

  {
     "data-root": "/path/to/data/root/"
  }

• storage-driver

  {
    "storage-driver": "vfs",
    "storage-opts": ["size=256M"]
  }

userns-remap

{
  "userns-remap": "testuser"
}

logs

[!NOTE|label:references:]

• Configure logging drivers
• Docker: How to clear the logs properly for a Docker container?

{
   "log-driver": "json-file",
   "log-opts": {
     "max-size": "1g",
     "max-file": "3"
  }
}

full sample file

{
  "allow-nondistributable-artifacts": [],
  "api-cors-header": "",
  "authorization-plugins": [],
  "bip": "",
  "bridge": "",
  "builder": {
    "gc": {
      "enabled": true,
      "defaultKeepStorage": "10GB",
      "policy": [
        { "keepStorage": "10GB", "filter": ["unused-for=2200h"] },
        { "keepStorage": "50GB", "filter": ["unused-for=3300h"] },
        { "keepStorage": "100GB", "all": true }
      ]
    }
  },
  "cgroup-parent": "",
  "containerd": "/run/containerd/containerd.sock",
  "containerd-namespace": "docker",
  "containerd-plugins-namespace": "docker-plugins",
  "data-root": "",
  "debug": true,
  "default-address-pools": [
    {
      "base": "172.30.0.0/16",
      "size": 24
    },
    {
      "base": "172.31.0.0/16",
      "size": 24
    }
  ],
  "default-cgroupns-mode": "private",
  "default-gateway": "",
  "default-gateway-v6": "",
  "default-network-opts": {},
  "default-runtime": "runc",
  "default-shm-size": "64M",
  "default-ulimits": {
    "nofile": {
      "Hard": 64000,
      "Name": "nofile",
      "Soft": 64000
    }
  },
  "dns": [],
  "dns-opts": [],
  "dns-search": [],
  "exec-opts": [],
  "exec-root": "",
  "experimental": false,
  "features": {},
  "fixed-cidr": "",
  "fixed-cidr-v6": "",
  "group": "",
  "host-gateway-ip": "",
  "hosts": [],
  "proxies": {
    "http-proxy": "http://proxy.example.com:80",
    "https-proxy": "https://proxy.example.com:443",
    "no-proxy": "*.test.example.com,.example.org"
  },
  "icc": false,
  "init": false,
  "init-path": "/usr/libexec/docker-init",
  "insecure-registries": [],
  "ip": "0.0.0.0",
  "ip-forward": false,
  "ip-masq": false,
  "iptables": false,
  "ip6tables": false,
  "ipv6": false,
  "labels": [],
  "live-restore": true,
  "log-driver": "json-file",
  "log-level": "",
  "log-opts": {
    "cache-disabled": "false",
    "cache-max-file": "5",
    "cache-max-size": "20m",
    "cache-compress": "true",
    "env": "os,customer",
    "labels": "somelabel",
    "max-file": "5",
    "max-size": "10m"
  },
  "max-concurrent-downloads": 3,
  "max-concurrent-uploads": 5,
  "max-download-attempts": 5,
  "mtu": 0,
  "no-new-privileges": false,
  "node-generic-resources": [
    "NVIDIA-GPU=UUID1",
    "NVIDIA-GPU=UUID2"
  ],
  "oom-score-adjust": 0,
  "pidfile": "",
  "raw-logs": false,
  "registry-mirrors": [],
  "runtimes": {
    "cc-runtime": {
      "path": "/usr/bin/cc-runtime"
    },
    "custom": {
      "path": "/usr/local/bin/my-runc-replacement",
      "runtimeArgs": [
        "--debug"
      ]
    }
  },
  "seccomp-profile": "",
  "selinux-enabled": false,
  "shutdown-timeout": 15,
  "storage-driver": "",
  "storage-opts": [],
  "swarm-default-advertise-addr": "",
  "tls": true,
  "tlscacert": "",
  "tlscert": "",
  "tlskey": "",
  "tlsverify": true,
  "userland-proxy": false,
  "userland-proxy-path": "/usr/libexec/docker-proxy",
  "userns-remap": ""
}

{
  "allow-nondistributable-artifacts": [],
  "authorization-plugins": [],
  "bridge": "",
  "containerd": "\\\\.\\pipe\\containerd-containerd",
  "containerd-namespace": "docker",
  "containerd-plugins-namespace": "docker-plugins",
  "data-root": "",
  "debug": true,
  "default-network-opts": {},
  "default-runtime": "",
  "default-ulimits": {},
  "dns": [],
  "dns-opts": [],
  "dns-search": [],
  "exec-opts": [],
  "experimental": false,
  "features": {},
  "fixed-cidr": "",
  "group": "",
  "host-gateway-ip": "",
  "hosts": [],
  "insecure-registries": [],
  "labels": [],
  "log-driver": "",
  "log-level": "",
  "max-concurrent-downloads": 3,
  "max-concurrent-uploads": 5,
  "max-download-attempts": 5,
  "mtu": 0,
  "pidfile": "",
  "raw-logs": false,
  "registry-mirrors": [],
  "shutdown-timeout": 15,
  "storage-driver": "",
  "storage-opts": [],
  "swarm-default-advertise-addr": "",
  "tlscacert": "",
  "tlscert": "",
  "tlskey": "",
  "tlsverify": true
}

enable tcp port 2375 for external connection to docker

references:

• * Configure where the Docker daemon listens for connections
• * styblope/docker-api-port.md
• * Configure the daemon

  • Configure remote access for Docker daemon
  • Protect the Docker daemon socket
  • Configure and troubleshoot the Docker daemon
  • Control Docker with systemd
  • Configure the daemon for IPv6
  • Docker and iptables
• * Daemon socket option
• * Protect the Docker daemon socket

  • Create a CA, server and client keys with OpenSSL
  • Secure by default
• Docker security : Docker daemon attack surface

[!TIP]

• to check service

  $ sudo systemd-analyze verify <name.service>

• enable service if necessary

  $ sudo systemctl enable containerd.service
  Created symlink /etc/systemd/system/multi-user.target.wants/containerd.service → /usr/lib/systemd/system/containerd.service

# prepare
$ sudo systemctl stop docker.service
$ sudo systemctl stop docker.socket

• via daemon.json

  $ cat /etc/docker/daemon.json
  {
    "hosts": ["unix:///var/run/docker.sock", "tcp://127.0.0.1:2375"]
  }
  # or
  $ cat /etc/docker/daemon.json
  {
    "hosts": ["unix:///var/run/docker.sock", "fd://", "tcp://127.0.0.1:2375"]
  }
  
  $ sudo systemctl edit docker.service

• via override.conf

  $ cat /etc/systemd/system/docker.service.d/override.conf
  [Service]
  ExecStart=
  ExecStart=/usr/bin/dockerd -H fd:// -H tcp://127.0.0.1:2375 [--containerd=/run/containerd/containerd.sock] [--config-file /etc/docker/daemon.json]
  
  $ sudo systemctl daemon-reload
  $ sudo systemctl restart docker.service
  
  # result
  $ sudo netstat -lntp | grep dockerd
  tcp6       0      0 :::2375                 :::*                    LISTEN      5649/dockerd

• result

  $ sudo cat /etc/docker/daemon.json
  {
    "hosts": ["unix:///var/run/docker.sock", "fd://", "tcp://0.0.0.0:2375"]
  }
  
  $ sudo cat /etc/systemd/system/docker.service.d/docker.conf
  [Service]
  ExecStart=
  ExecStart=/usr/bin/dockerd
  
  $ docker -H tcp://0.0.0.0:2376 pull ubuntu:18.04
  18.04: Pulling from library/ubuntu
  a404e5416296: Pull complete
  Digest: sha256:ca70a834041dd1bf16cc38dfcd24f0888ec4fa431e09f3344f354cf8d1724499
  Status: Downloaded newer image for ubuntu:18.04

  • verify

    $ ip -4 a s en1
    5: en1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
        inet x.x.x.x/24 brd x.x.x.255 scope global noprefixroute en1
           valid_lft forever preferred_lft forever
    
    $ nc -zv <domain.com> 2375
    Connection to domain.com 2375 port [tcp/*] succeeded!
    
    $ docker -H tcp://<domain.com>:2375 images
    REPOSITORY   TAG       IMAGE ID       CREATED       SIZE
    ubuntu       18.04     71eaf13299f4   2 weeks ago   63.1MB

• or modify in /lib/systemd/system/docker.service

  [!TIP]

  • Troubleshoot conflicts between the daemon.json and startup scripts

  --- Replacing this line:
  ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
  ---                        ╰╴╴╴╴╴╴╯
  ---                     remove `-H fd://`
  
  +++ With this line:
  ExecStart=/usr/bin/dockerd --containerd=/run/containerd/containerd.sock [--tls=false]

• or via socat

  exec socat -d TCP-LISTEN:2375,fork UNIX-CONNECT:/var/run/docker.sock

$ sudo cat /usr/lib/systemd/system/docker.service
[Unit]
Description=Docker Application Container Engine
Documentation=https://docs.docker.com
After=network-online.target docker.socket firewalld.service containerd.service time-set.target
Wants=network-online.target containerd.service
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
#         remove if enable remote access in /etc/docker/daemon.json
#                          ╭╴╴╴╴╴╴╮
ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock
ExecReload=/bin/kill -s HUP $MAINPID
TimeoutStartSec=0
RestartSec=2
Restart=always

# Note that StartLimit* options were moved from "Service" to "Unit" in systemd 229.
# Both the old, and new location are accepted by systemd 229 and up, so using the old location
# to make them work for either version of systemd.
StartLimitBurst=3

# Note that StartLimitInterval was renamed to StartLimitIntervalSec in systemd 230.
# Both the old, and new name are accepted by systemd 230 and up, so using the old name to make
# this option work for either version of systemd.
StartLimitInterval=60s

# Having non-zero Limit*s causes performance problems due to accounting overhead
# in the kernel. We recommend using cgroups to do container-local accounting.
LimitNOFILE=infinity
LimitNPROC=infinity
LimitCORE=infinity

# Comment TasksMax if your systemd version does not support it.
# Only systemd 226 and above support this option.
TasksMax=infinity

# 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
OOMScoreAdjust=-500

[Install]
WantedBy=multi-user.target