How do enable Experimental Docker daemon in Azure Pipelines on hosted Ubuntu agent

Question

I want to be able to use the --squash switch when building docker images as this shaves several MB of the result image.

This requires experimental features enabled for docker.

Executing a docker --version confirms (as it should) experimental features to be off on hosted Azure Pipelines agents.

Server:
 Engine:
  Version:  18.03.1-ce
  API version:  1.37 (minimum version 1.12)
  Go version:   go1.9.5
  Git commit:   9ee9f40
  Built:    Thu Apr 26 07:15:30 2018
  OS/Arch:  linux/amd64
  Experimental: false

Linux agents are running

Kernel Version: 4.15.0-1022-azure
Operating System: Ubuntu 16.04.4 LTS
OSType: linux
Architecture: x86_64

I've tried altering /etc/systemd/system/docker.service.d/docker.conf and /etc/docker/daemon.json to start with/include experimental flags, but didn't succeed in enabling it.

docker.conf

[Service]
ExecStart=
ExecStart=/usr/bin/dockerd -H fd:// --experimental=tr

or

daemon.json

{ 
    "experimental": true 
} 

But don't unsure if I can restart the daemon on a hosted agent.

Currently doing yaml builds invoking docker from bash, but didn't see anything around experimental in the web interface either.

If i spin up my own Ubuntu VM and host an agent on that, experimental works, but want to avoid cost and maintenance by using the hosted agents.

Answer 1

In the Ubuntu Image you can simply restart the docker service, after the daemon.json is updated. I use a script with two lines:

echo '{ "experimental": true }' | sudo tee /etc/docker/daemon.json
sudo service docker restart