General Information

Installing and configuring docker.

• Docker Versions Change Log - Change branches to see different change logs
  • 17.12: https://github.com/docker/docker-ce/blob/17.12/CHANGELOG.md

Checklist

• CentOS 7

Docker has switched from docker-engine packages to docker-ce (community edition) and docker-ee (enterprise edition).

docker-engine-ce's last version was 17.05.

Official documentation: https://docs.docker.com/engine/installation/linux/docker-ce/centos/

• Ensure system is updated

  sudo yum update

• Add the Docker repo
  • Repo

    yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

  • Add the GPG key

    rpm --import https://download.docker.com/linux/centos/gpg

• Install Docker
  • CE (community edition)

    yum install docker-ce

Docker Data and Meta Data

• Create a “thin” logical volume using all of the space on a physical volume

  sudo lvcreate --extents 100%PVS --thin --name lvdockerpool vglocal /dev/sdX1

  • This thin logical volume will be used by the docker daemon directly to automatically setup a file system and allocate space for docker data and metadata.
  • NOTE: This space is NOT used for docker container image storage. (/var is the default)

If you ever need to increase docker container data storage OR metadata storage, they can be resized individually.

• Resize docker pool metadata example (increase by 1 GB)

  lvextend --size +1G -n vglocal/lvdockerpool_tmeta

• Resize docker pool storage example (increase by 10 GB)

  lvextend --size +10G -n vglocal/lvdockerpool_tdata

Docker container image storage (/var)

• If /var needs more space for container image storage, run the following (example)

  sudo lvextend --resizefs --size +7G /dev/vglocal/lvvar

Service Setup

• Override default docker.service startup options
  • Create a systemd docker.service override directory

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

• Create a docker.service override file
  • Docker 1.12 (2016-07-28) - 17.12.0-ce (2017-12)

    tee /etc/systemd/system/docker.service.d/docker.conf <<-'EOF'
    [Service]
    EnvironmentFile=
    EnvironmentFile=-/etc/sysconfig/docker
    ExecStart=
    ExecStart=/usr/bin/dockerd $OPTIONS
    EOF

  • The blank variable setting ensures that no default settings are appended to the overrides.

• Setup docker daemon startup options
  • Docker 1.12 (2016-07-28) - 17.12.0-ce (2017-12)

    tee /etc/sysconfig/docker <<-'EOF'
    # Modify these options if you want to change the way the docker daemon runs
    OPTIONS=--storage-driver=devicemapper --storage-opt dm.thinpooldev=vglocal-lvdockerpool --storage-opt dm.use_deferred_deletion=true --storage-opt dm.use_deferred_removal=true
    EOF

• Reload the systemd daemon for the override file to be picked up

  systemctl daemon-reload

• Start the Docker engine, enable on boot, and check status

  sudo systemctl start docker
  sudo systemctl enable docker
  sudo systemctl status docker

• Verify docker was started with the correct options

  ps -elf | grep docker | grep -v grep

• Run the test image to ensure it is installed correctly

  sudo docker run hello-world

• Create the “docker” group and add users to it

  sudo usermod -aG docker <username>

  • Multiple users example

    for x in user1 user2 user3; do sudo usermod -aG docker $x; done

• Log out/log back in
• Verify the user can run docker commands without using sudo

  docker run hello-world

• Symptom: Docker service fails to start
• Error Seen In Logs: Error starting daemon: error initializing graphdriver: devicemapper: Non existing device vglocal-lvdockerpool
• Why: /var/lib/docker contains metadata telling docker about the contents of device mapper storage. When /var/lib/docker is removed, metadata is lost. Then docker will detect the thin pool has data, but docker is unable to use it.
• Official Documentation: https://access.redhat.com/solutions/2281281

The Fix

• Stop docker

  systemctl stop docker

• Remove the docker thin pool logical volume

  lvremove /dev/vglocal/lvdockerpool

• Re-create it (example using 100% of /dev/sde1)

  lvcreate --extents 100%PVS --thin --name lvdockerpool vglocal /dev/sde1