How to configure Unicorn with a volume mapping for your CM server Docker container

docker-compose.yml

  cm:
    image: sitecore-xp-sxa-1.9.0-standalone:9.2.0-windowsservercore-${WINDOWSSERVERCORE_CHANNEL}
    entrypoint: cmd /c "start /B powershell Watch-Directory C:/src C:/inetpub/sc & C:\\remote_debugger\\x64\\msvsmon.exe /noauth /anyuser /silent /nostatus /noclrwarn /nosecuritywarn /nofirewallwarn /nowowwarn /timeout:2147483646"
    volumes:
      - C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\Common7\IDE\Remote Debugger:C:\remote_debugger:ro
      - .\deploy:C:\src
      - .\unicorn:C:\unicorn
      - .\data\cm:C:\inetpub\sc\App_Data\logs
      - .\data\creativeexchange:C:\inetpub\sc\App_Data\packages\CreativeExchange\FileStorage
    ports:
      - "44001:80"
    links:
      - sql
      - solr
      - xconnect
 
Only this part is relevant to Unicorn. It will map your solutionroot/unicorn to C:\unicorn in the container

    volumes:
      - .\unicorn:C:\unicorn

Setup Unicorn in Docker.txt

How to set up Unicorn in your Docker container

Since all writing to Unicorn files happens inside the container, and the container is now linked to .\unicorn, 
all you need to do is ensure that .\unicorn is included under source control.

This gets even better if you use Transparent Sync.

Unicorn.TargetDataStore.config

Place this in App_Config/Include/z.Unicorn

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
	<sitecore>
		<unicorn>
			<defaults>
				<targetDataStore>
					<patch:attribute name="physicalRootPath">c:\unicorn\$(configurationName)</patch:attribute>
				</targetDataStore>
			</defaults>
		</unicorn>
	</sitecore>
</configuration>