# Docker

ApisCP does not yet provide direct support for Docker, but it's easy to integrate into ApisCP.

# Installation

Unsafe for multi-tenant operations

The instructions contained herein assume you are the only person managing accounts on this server.

# CentOS 7

Install the docker package using yum, then replicate it into the filesystem template.

yum install -y docker
/usr/local/apnscp/bin/scripts/yum-post.php install -d docker siteinfo
mkdir -p /home/virtual/FILESYSTEMTEMPLATE/siteinfo/etc/sysconfig
cp -dp /etc/sysconfig/docker /home/virtual/FILESYSTEMTEMPLATE/siteinfo/etc/sysconfig/
systemctl reload fsmount

Files in /etc/sysconfig are typically skipped during filesystem replication. Populate this file to avoid any complications during initialization.

CentOS 7 rhsm hotfix

Broken package dependencies create a circular link in CentOS 7 for RedHat's subscription manager, required by Docker. Remove the dangling link, then download the CA/intermediate certs directly from RedHat (CentOS #14785 (opens new window)):

rm -f /etc/rhsm/ca/redhat-uep.pem
openssl s_client -showcerts -servername registry.access.redhat.com -connect registry.access.redhat.com:443 </dev/null 2>/dev/null | openssl x509 -text > /etc/rhsm/ca/redhat-uep.pem
cp -fpldR /etc/rhsm /home/virtual/FILESYSTEMTEMPLATE/siteinfo/etc/

# CentOS 8/Stream

docker-ce package replaces docker in CentOS 8. CentOS 8 replaces Docker with Podman (opens new window) as a noteworthy alternative. To run Docker on a CentOS 8+ platform, Cockpit must be removed as well as an additional repository added that contains docker-ce and dependencies.

dnf config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
dnf install -y --allowerasing docker-ce
/usr/local/apnscp/bin/scripts/yum-post.php install -d docker-ce siteinfo
systemctl reload fsmount

Docker's default configuration inhibits listening in other locations. It will be overrode with a custom systemd service definition that omits -H fd:// (see #22339 (opens new window), #21559 (opens new window), #25471 (opens new window), PR#27473 (opens new window)).

mkdir -p /etc/systemd/system/docker.service.d
cat << EOF > /etc/systemd/system/docker.service.d/override.conf
# This clears any ExecStart= inherited from docker.service
ExecStart=/usr/bin/dockerd --containerd=/run/containerd/containerd.sock
systemctl daemon-reload

# Final setup

Add a group named docker. This group will be used to authorize any user to use the Docker service. We'll come back to this later, adding the group for each site that will have Docker access.

groupadd --system docker 2> /dev/null

Reconfigure Docker to expose its Unix socket to an accessible location within the filesystem template.

systemctl enable --now docker
echo -e '{\n\t"hosts": ["unix:///var/run/docker.sock", "unix:///.socket/docker.sock"],\n\t"group": "docker"\n}' > /etc/docker/daemon.json
systemctl restart docker
ln -s  /.socket/docker.sock /home/virtual/FILESYSTEMTEMPLATE/siteinfo/var/run/docker.sock
systemctl reload fsmount

# Authorizing Docker usage per site

For each site to enable Docker, create the group then add the Site Administrator (or any sub-user) to the docker group.

Assume we're adding the Site Administrator for apiscp.com to use Docker. get_config, a CLI helper, will help lookup the Site Administrator (admin_user field) for a given site.

chroot /home/virtual/apiscp.com/ groupadd --system -g "$(getent group docker | cut -d: -f3)" docker
chroot /home/virtual/apiscp.com/ usermod -G docker -a "$(get_config apiscp.com siteinfo admin_user)"
# Switch to the Site Admin for apiscp.com
su apiscp.com
# Confirm the user is part of "docker" group
# Sample response:
# uid=9999(myadmin) gid=1000(myadmin) groups=1000(myadmin),10(wheel),978(docker)

# First container

For a hypothetical first run app, Apache Zeppelin (opens new window) is used as it's what initiated this document.

Create a subdomain or addon domain. Inside the document root (opens new window) add a .htaccess (opens new window) file that will proxy all requests to the container.

For example, if the port argument is --port 8082:8080 then externally, 8082 is being forwarded internally to the Docker container expecting traffic on 8080. Knowing this, prepare the .htaccess file:

DirectoryIndex disabled

RewriteEngine On
RewriteCond %{HTTP:Connection} =upgrade [NC]
RewriteCond %{HTTP:Upgrade} =websocket [NC]
RewriteRule ^(.*)$ ws://localhost:8082/$1 [L,QSA,P]
RewriteRule ^(.*)$ http://localhost:8082/$1 [L,QSA,P]

Websocket disabled by default

Enable Websocket support by loading the wstunnel (opens new window) module. Not every application utilizes Websockets, so check with your vendor documentation. Zeppelin requires Websocket for use.

Add LoadModule proxy_wstunnel_module modules/mod_proxy_wstunnel.so to /etc/httpd/conf/httpd-custom.conf, then run htrebuild to activate configuration changes.

Disabling index negotiation

Apache will try multiple files to determine which file to serve when no file is explicitly provided in the request URI. Disabling an index ensures this request - without a filename - is passed directly to your Docker instance for resolution.

Run Zeppelin, and you're done!

docker run -d  -p 8082:8080 --name zeppelin apache/zeppelin:0.9.0 

To list active containers, run docker container list. To stop a container, run docker stop CONTAINER-ID. Adding --rm to the task creates a volatile container (opens new window), which will remove created data on exit.

This task may be added to boot on startup using the @reboot token in crond:

crontab -e
# Next add the following line
@reboot docker run -d  -p 8082:8080 --name zeppelin apache/zeppelin:0.9.0 

# Container management

Portainer (opens new window) is a tool made for managing a collection of Docker containers. Given the sensitive nature of sending credentials across the wire, this subdomain (portainer.apiscp.com) will require HTTPS and set an HTTP strict transport security header to ensure future connections use SSL.

Portainer Dashboard

First create the persistent volume store, then run it.

docker volume create portainer_data
docker run -d -p 8000:8000 -p 9000:9000 --name=portainer --restart=always -v /var/run/docker.sock:/var/run/docker.sock -v portainer_data:/data portainer/portainer

Lastly, connect it using Apache to the backend container.

DirectoryIndex disabled

RequestHeader set X-Forwarded-Proto "https"
Header always set Strict-Transport-Security "max-age=63072000;"

RewriteEngine On
RewriteCond %{HTTPS} !=on
RewriteRule ^(.*)$ https://%{HTTP_HOST}/$1 [R,L]

RewriteCond %{HTTP:Connection} =upgrade [NC]
RewriteCond %{HTTP:Upgrade} =websocket [NC]
RewriteRule ^(.*)$ ws://localhost:9000/$1 [L,QSA,P]
RewriteRule ^(.*)$ http://localhost:9000/$1 [L,QSA,P]

That's all there is!

# Adding docker-compose

docker-compose is a tool (opens new window) for defining and running multi-container Docker applications. It requires Python 3.6+, which can be installed on a per-site basis.

su apiscp.com
# Compile Python 3.6.5
pyenv install 3.6.5
# Set Python 3.6.5 globally for this account
pyenv global 3.6.5
# Install docker-compose
pip install docker-compose
# Confirm it's installed
docker-compose  -v
# Reports: "docker-compose version 1.28.2, build unknown"

# Security

This current implementation of Docker is not suitable in a multi-administrator environment. Users within other domains may see and manage Docker containers. There are plans to implement RBAC and bring Docker as a permanent fixture to ApisCP, but for now only one authorized user may use Docker on a server.

If the same group treatment is applied to another domain, for instance, that user also has visibility of the Docker containers:

chroot /home/virtual/apisnetworks.com/ groupadd --system -g "$(getent group docker | cut -d: -f3)" docker
chroot /home/virtual/apisnetworks.com/ usermod -G docker -a "$(get_config apisnetworks.com siteinfo admin_user)"
su apisnetworks.com
docker container ls
# CONTAINER ID        IMAGE                   COMMAND                  CREATED             STATUS              PORTS                                            NAMES
# 13d1ed48ff42        portainer/portainer     "/portainer"             8 hours ago         Up 8 hours>8000/tcp,>9000/tcp   portainer
# f1a5e11a3cc9        apache/zeppelin:0.9.0   "/usr/bin/tini -- ..."   9 hours ago         Up 9 hours>8080/tcp                           zeppelin

Secondly, in the above examples, Docker privileges are bestowed to the Site Administrator of an account via usermod. In normal configuration, PHP-FPM runs as a separate, unprivileged user (apache). This feature may be changed by editing the service parameter apache,webuser to match the Site Administrator. In such configurations, an exploit in PHP would permit an attacker access to all docker commands.

Never grant a PHP-FPM user Docker privileges. Never designate a Docker user as apache,webuser.

EditDomain -c apache,webuser="$(get_config apisnetworks.com siteinfo admin_user)" apisnetworks.com
chroot /home/virtual/apisnetworks.com/ usermod -G docker -a "$(get_config apisnetworks.com siteinfo admin_user)"
# ^^^ BZZZT. WRONG. ^^^