Is it possible to start multiple docker daemons on the same machine

Question

And if it is possible, how would you configure each daemon - graph location, images location, etc?

Answer 1

Yes, it's perfectly possible to run two Docker daemons on a single host even without Docker Machine. As of Docker 18.09.0-ce, the following dockerd flags are the ones that could cause conflicts if two daemons used the defaults:

  -b, --bridge string       Attach containers to a network bridge       --exec-root string    Root directory for execution state files (default "/var/run/docker")       --data-root string    Root directory of persistent Docker state (default "/var/lib/docker")   -H, --host list           Daemon socket(s) to connect to   -p, --pidfile string      Path to use for daemon PID file (default "/var/run/docker.pid") 

• The default for --bridge is docker0, and if you're not using the default, you must create and configure the bridge manually (Docker won't create/manage it for you). More details below.

• --exec-root is where container state is stored (default: /var/run/docker).

• --data-root is where images are stored (default: /var/lib/docker).

• --host specifies where the Docker daemon will listen for client connections. If unspecified, it defaults to /var/run/docker.sock.

• --pidfile is where the process ID of the daemon is stored (default: /var/run/docker.pid).

So, as long as your two daemons use different values for these flags, you can run them on the same host. Example script (including network setup):

#!/bin/sh ## name: altdocker.sh set -e -x  : ${bridge=altdocker} : ${base=$HOME/$bridge}  # Set up bridge network: if ! ip link show $bridge > /dev/null 2>&1 then    sudo ip link add name $bridge type bridge    sudo ip addr add ${net:-"10.20.30.1/24"} dev $bridge    sudo ip link set dev $bridge up fi  sudo dockerd \   --bridge=$bridge \   --data-root=$base.data \   --exec-root=$base.exec \   --host=unix://$base.socket \   --pidfile=$base.pid 

Example usage:

## in one terminal $ env net=10.9.8.7/24 /bin/sh altdocker.sh # ... log output ...  ## in another terminal $ docker -H unix://$HOME/altdocker.socket run --rm -i -t alpine sh / # echo hereiam hereiam 

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Updated for changes from Docker 1.9.1 to 18.09.0-ce, in case anyone is using a very old version:

┌───────────────┬─────────────┐ │ 1.9.1         │ 18.09.0-ce  │ ├───────────────┼─────────────┤ │ docker daemon │ dockerd     │ │ -g / --graph  │ --exec-root │ └───────────────┴─────────────┘ 

Answer 2

Great question! It is possible to start a Docker daemon inside a container. In that container you would be able to start more containers. This way you can run docker daemons with different settings on the same host machine.

Checkout this project: https://github.com/jpetazzo/dind. It provides a Docker image that contains Docker itself, just as you require.