Docker

linux, docker, cli, installation, network, volume, iptables, nftables, portainer

Docker

Docker is a set of platform as a service (PaaS) products that use OS-level virtualization to deliver software in packages called _containers_. The service has both free and premium tiers. The software that hosts the containers is called Docker Engine.

Project Homepage: [Home - Docker](https://www.docker.com/)
Documentation: [Docker Documentation | Docker Documentation](https://docs.docker.com/)
Docker hub: [Docker hub](https://hub.docker.com)

Installation

Install Docker Engine on Debian

One click installation script:

curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh get-docker.sh

Note for Debian testing just use sudo apt install docker, as testing packages the latest docker and the docker repo does not seem to have testing.

Run docker as non root user:

sudo groupadd docker
sudo usermod -aG docker $USER

Install Docker Engine : [Docker Engine](https://docs.docker.com/engine/install/)

Docker Desktop for Linux

I have preferred to run Docker command as a native Linux applications. Docker Desktop originally was created to allow operating systems other than Linux to run Docker by creating a virtual Linux machine to operate them within. Linux does not need this as the various docker programs run natively. A version of Docker Desktop was created for Linux that looks like it has some additional user interface features, but to date I have not wanted to setup an additional VM for this purpose and am happy to continues to use the Linux KVM VM solution.

Uninstall

Both the install methods actually use the standard package manager to install docker.

dpkg -l|grep docker to check the docker packages actually installed and which docker packages and versions are installed
sudo apt remove docker-ce
Check the the var/lib/docker directory, sudo du -d 1 -h var/lib/docker
rm -rf /var/lib/docker to remove the docker directory. I try not to store any important files in docker, so this should be low risk for me.

Uninstall docker version installed via script

Docker and iptables on Host

Docker applies iptables on the host machine, see Docker and iptables.

A Docker host that is acting or running as a router, e.g. using Traefik, the following may be needed to allow operation.

For some more details, tldr;

This may affect other services operating on the host machine. The default FORWARD chain is set to DROP. On my existing home web server this effectively stopped the KVM bridge network from operating, so the virtual machines could not communicate outside the local host IP address with other LAN addresses, including the router / gateway.

Linux forwarding is required for Docker and can be checked with sudo sysctl net.ipv4.ip_forward.

It would also adversely affect my Linux router should I attempt to load docker on this machine. To make matters worse my Linux router is based on nftables which may not operate well with iptables. I will cross that hurdle should I get there. Interestingly, it would seem that iptables operates on/as nftables in the Debian 11.

As perDocker and iptables. Docker on a router the “simple” solution is to add FORWARD ACCEPT rules to the DOCKER-USER chain as required, e.g.: iptables -I DOCKER-USER -i src_if -o dst_if -j ACCEPT. For the machine in question this became sudo iptables -I DOCKER-USER -i br0 -o br0 -j ACCEPT, where br0 was the bridge interface for the VMs and also LAN access. The next problem was how to make this occur automagically after a reboot. I added a new systemd.service for this: sudo vim /etc/systemd/system/iptables-docker.service:

[Unit]
Description=IPTables Docker Rules
After=docker.service

[Service]
Type=oneshot
ExecStart=/usr/sbin/iptables -I DOCKER-USER -i br0 -o br0 -j ACCEPT

[Install]
WantedBy=multi-user.target

As I was just adding a single rule to one chain I simply ran the iptables command as a oneshot service after the docker.service. If I needed a more complex iptable configuration I could have created a file called iptables-docker.rules in /etc/iptables/rules.v4 and then used command iptables-restore -nv < /etc/iptables/rules.v4 or some such in the docker.service.

Some hand commands:

sudo iptables -S to see the current iptable rules
sudo nft list ruleset lists as nftable rules
whereis iptables to find the full path for the iptables command.
systemctl daemon-reload to reload the system service file if modified
sudo systemctl enable iptables-docker.service to enable the service to function automatically, e.g. at startup, on multi-user-target

DNS and nftable / iptables / netfilter within containers

Docker has to perform some interesting network filtering both on the container host, as noted above and within containers as outlined here. It looks like this is required to allow container DNS functionality on Docker containers using bridge networking.

The containers DNS (/etc/resolv.conf) is assigned to a proxy on 127.0.0.11:53. (Note that DNS uses UDP not TCP datagrams.)

Further to this The container netfilter use NAT chains to operate on 127.0.0.11. See the following nftables info:

nft list tables

table ip nat

nft list table ip nat

# Warning: table ip nat is managed by iptables-nft, do not touch!
table ip nat {
	chain DOCKER_OUTPUT {
		meta l4proto tcp ip daddr 127.0.0.11 xt match "tcp" counter packets 0 bytes 0 xt target "DNAT"
		meta l4proto udp ip daddr 127.0.0.11 xt match "udp" counter packets 329 bytes 20249 xt target "DNAT"
	}

	chain OUTPUT {
		type nat hook output priority dstnat; policy accept;
		ip daddr 127.0.0.11 counter packets 329 bytes 20249 jump DOCKER_OUTPUT
	}

	chain DOCKER_POSTROUTING {
		meta l4proto tcp ip saddr 127.0.0.11 xt match "tcp" counter packets 0 bytes 0 xt target "SNAT"
		meta l4proto udp ip saddr 127.0.0.11 xt match "udp" counter packets 0 bytes 0 xt target "SNAT"
	}

	chain POSTROUTING {
		type nat hook postrouting priority srcnat; policy accept;
		ip daddr 127.0.0.11 counter packets 329 bytes 20249 jump DOCKER_POSTROUTING
	}
}
/ #

On VPN setup, at least openvpn, the /etc/resolv.conf is overwritten anyway so the Docker netfilter chains become irrelevant.

On the other hand where Docker bridge network DNS container name resolution is desirable then these netfilter chains must basically remain unadulterated. So in these cases where I need to used netfilter within the container, the simple solution is to simply add extra chains without using the nft flush ruleset command first. These means that if subsequent rule changes are made the container will need to be recreated. This is effectively only for simple basic filter (input, output & forward) chains only, more complex netfilter nat requirements would need further consideration.

Portainer

Portainer is a handy web view into the Docker system. It can be loaded on the host as a Docker container as per this docker documentation Install Portainer with Docker on Linux! A lot of the official Portainer web points to the business version. They do allow 5 free business installations with registration. The portainer-ee image is the business image on Docker hub, portainer-ce is the community addition. When downgrading from the business edition to the community edition the database on the volume storage needs to be downgraded or portainer-ce will not start.

The community addition command is:

docker volume create portainer_data
docker run -d -p 9443:9443 --name=portainer --restart=always \
    -v /var/run/docker.sock:/var/run/docker.sock \
    -v portainer_data:/data \
    portainer/portainer-ce:latest

Notes:

The port 8000 (-p 8000:8000) is not normally required on community edition. Further to this Kea dhcp control agent uses port 8000 as default.
Some browsers give strange message if http access is requested and then require exception for dodgy https certificate.

Portainer agent

Portainer agent allows a remote docker machine to be seen else were via the network. Default port seems to be 9001.

First stop the agent container: docker stop portainer_agent
Then remove the agent container: docker rm portainer_agent
Then pull the latest portainer/agent: docker pull portainer/agent, default is latest if version is not specified.

docker run -d   -p 9001:9001   --name portainer_agent   --restart=always -v /var/run/docker.sock:/var/run/docker.sock -v /var/lib/docker/volumes:/var/lib/docker/volumes portainer/agent

Docker CLI

Much of this material was originally sourced from: cheat-sheets/docker/docker.md

Run Containers

COMMAND	DESCRIPTION
`docker run IMAGE`	Start a new container
`docker run --name CONTAINER IMAGE`	Start a new container and set a name
`docker run -p HOSTPORT:CONTAINERPORT IMAGE`	Start a new container with mapped ports
`docker run -P IMAGE`	Start a new container and map all ports
`docker run -d IMAGE`	Start a new container in background
`docker run -v HOSTDIR:TARGETDIR IMAGE`	Map local directory and Launch

Container Management:

COMMAND	DESCRIPTION
`docker ps`	Show a list of all running containers
`docker ps -a`	Show a list of all containers
`docker create IMAGE`	Create a new container
`docker start CONTAINER`	Start a container
`docker stop CONTAINER`	Graceful stop a container
`docker kill CONTAINER`	Kill (SIGKILL) a container
`docker restart CONTAINER`	Graceful stop and restart a container
`docker pause CONTAINER`	Suspend a container
`docker unpause CONTAINER`	Resume a container
`docker rename OLD NEW`	Rename a container
`docker rm CONTAINER`	Destroy a container
`docker rm -f CONTAINER`	Destroy a running container
`docker exec -it CONTAINER COMMAND`	Run a command in a container
`docker exec -it CONTAINER bash`	Run bash shell in a container as default user, usually root
`docker exec -it --user www-data CONTAINER bash`	Run bash shell in a container as defined user

Not that in many simple Alpine containers bash is not the default sh, ash or sh is more likely.

Container Bulk Management

COMMAND	DESCRIPTION
`docker stop $(docker ps -q)`	To stop all the running containers
`docker stop $(docker ps -a -q)`	To stop all the stopped and running containers
`docker kill $(docker ps -q)`	To kill all the running containers
`docker kill $(docker ps -a -q)`	To kill all the stopped and running containers
`docker restart $(docker ps -q)`	To restart all running containers
`docker restart $(docker ps -a -q)`	To restart all the stopped and running containers
`docker rm $(docker ps -q)`	To destroy all running containers
`docker rm $(docker ps -a -q)`	To destroy all the stopped and running containers
`docker pause $(docker ps -q)`	To pause all running containers
`docker pause $(docker ps -a -q)`	To pause all the stopped and running containers
`docker start $(docker ps -q)`	To start all running containers
`docker start $(docker ps -a -q)`	To start all the stopped and running containers
`docker rm -vf $(docker ps -a -q)`	To delete all containers including its volumes use
`docker rmi -f $(docker images -a -q)`	To delete all the images
`docker system prune`	To delete all dangling and unused images, containers, cache and volumes
`docker system prune -a`	To delete all used and unused images
`docker system prune --volumes`	To delete all docker volumes

Inspect / Troubleshoot Containers:

COMMAND	DESCRIPTION
`docker ps`	List running containers
`docker ps -a`	List all containers, including stopped
`docker logs CONTAINER`	Show a container output
`docker logs -f CONTAINER`	Follow a container output
`docker top CONTAINER`	List the processes running in a container
`docker diff`	Show the differences with the image (modified files)
`docker inspect`	Show information of a container (json formatted)
`docker stats`	Show stats
`docker port CONTAINER`	Show mapped port of a container

Run Commands:

COMMAND	DESCRIPTION
`docker attach CONTAINER`	Attach to a container
`docker cp CONTAINER:PATH HOSTPATH`	Copy files from the container
`docker cp HOSTPATH CONTAINER:PATH`	Copy files into the container
`docker export CONTAINER`	Export the content of the container (tar archive)
`docker exec CONTAINER`	Run a command inside a container
`docker exec -it CONTAINER /bin/bash`	Open an interactive shell inside a container (there is no bash in some images, use /bin/sh)
`docker wait CONTAINER`	Wait until the container terminates and return the exit code

Images:

COMMAND	DESCRIPTION
`docker images`	List all local images
`docker history IMAGE`	Show the image history
`docker inspect IMAGE`	Show information (json formatted)
`docker tag IMAGE TAG`	Tag an image
`docker commit CONTAINER IMAGE`	Create an image (from a container)
`docker import URL`	Create an image (from a tarball)
`docker rmi IMAGE`	Delete images
`docker pull REPO:[TAG]`	pull an image/repo from a registry
`docker push REPO:[TAG]`	push and image/repo to a registry
`docker search TEXT`	Search an image on the official registry
`docker login`	Login to a registry
`docker logout`	Logout from a registry
`docker save REPO:[TAG]`	Export an image/repo as a tarball
`docker load`	Load images from a tarball
`docker build DIRECTORY`	Build an image from a docker file

Volumes:

COMMAND	DESCRIPTION
`docker volume ls`	List all volumes
`docker volume create VOLUME`	Create a volume
`docker volume inspect VOLUME`	Show information (json formatted)
`docker volume rm VOLUME`	Destroy a volume
`docker volume ls --filter="dangling=true“`	List all dangling volumes (not referenced by any container)
`docker volume prune`	Delete all volumes (not referenced by any container)

docker ps command

The docker ps command output is long and often difficult to read on the terminal for this reason.

docker ps --format 'table {{ .ID }}\t{{.Image}}\t{{ .Names }}'

CONTAINER ID   IMAGE                    NAMES

docker ps -s --format 'table {{ .ID }}\t{{.Status}}\t{{.Image}}\t{{ .Names }}'

CONTAINER ID   STATUS                  IMAGE                 NAMES

docker ps -s --format 'table {{ .ID }}\t{{.Status}}\t{{.Image}}\t{{ .Names }}\t{{.Size}}'

CONTAINER ID   STATUS                  IMAGE                 NAMES               SIZE

reference

How to change the docker ps output format
Docker Docs
- docker container ls
- Container size on disk

Backup a container

Backup docker data from inside container volumes and package it in a tarball archive.
docker run --rm --volumes-from CONTAINER -v $(pwd):/backup busybox tar cvfz /backup/backup.tar CONTAINERPATH

Restore container from backup

Restore the volume with a tarball archive.
docker run --rm --volumes-from CONTAINER -v $(pwd):/backup busybox sh -c "cd CONTAINERPATH && tar xvf /backup/backup.tar --strip 1"

Volumes

Docker volume types:

Host Volumes: -v /path/on/host:/path/in/container
Anonymous Volumes: -v /path/in/container
Named Volumes: -v name:/path/in/container

Docker controlled volumes are stored at /var/lib/docker/volumes

Networks

Type of networks on Docker:

Default Bridge (The default separate isolated bridge network.)
- This is the default network used if nothing else is defined
User defined bridge (DNS name resolution on Docker containers, which default bridge does not.)
- docker network create network_named
Host (Appears on the host machine as if installed there, no separate network.)
MACVLAN
1. MACVLAN (without subVLAN) this create a new ip address on the host machine
  - ```
  docker network create -d macvlan \
  --subnet 192.168.1.0/24 \
  --gateway 192.168.1.1 \
  -o parent=br0 \
  network_named
```
- No host DHCP access so need to specify ip address when creating container (docker cli --ip 192.168.1.14). If not specified docker DHCP will assign and could cause clash with host.
- May be problem with multiple MACs on common switch port. Need to set promiscuous mode on network, e.g. sudo ip link set br0 promisc on.
2. MACVLAN with subVLAN - never had to use this yet myself, so do not know much about it, something about trunking on a common link.
IPVLAN
1. IPVLAN on host subnet, this create a new ip address on the host machine, but not with new MAC number, it uses the host MAC number
  - ```
  docker network create -d ipvlan \
  --subnet 192.168.1.0/24 \
  --gateway 192.168.1.1 \
  -o parent=br0 \
  network_named
```
- No host DHCP access so need to specify ip address when creating container (docker cli --ip 192.168.1.14). If not specified docker DHCP will assign and could cause clash with host.
- May be problem with shared MAC with multiple IP address, but less likely than MACVLAN.
2. IPVLAN on separate subnet using the host machine as gateway, but not with new MAC number, it uses the host MAC number
  - ```
  docker network create -d ipvlan \
  --subnet 192.168.1.0/24 \
  -o parent=br0 -o ipvlan_mode=l3 \
  --subnet 192.168.10.0/24 \
  network_named
```
- No host DHCP access so need to specify ip address when creating container (docker cli --ip 192.168.1.14). If not specified docker DHCP will assign and could cause clash with host.
- May be problem with shared MAC with multiple IP address, but less likely than MACVLAN.
Overlay network, an even more obscure network arrangement I know nothing about.
None network - no assigned network, container has no external network connectivity

network troubleshooting

A lot of containers are setup to be small and hence do not include many, if any of the tools required to diagnose problems. A small docker image netshoot includes the most common networking tools and when attached to the same docker network can be used to diagnose the network and containers networks thereon.

docker run --rm --name netshoot --network proxy -it nicolaka/netshoot /bin/bash

Troubleshooting

netshoot: a Docker + Kubernetes network trouble-shooting swiss-army container docker run --name netshoot --rm -it nicolaka/netshoot /bin/bash
Docker - How to cleanup (unused) resources

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