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PowerShell: backup Docker containers


I have to reinstall my computer several times in a year, and I need to keep backup of my different stuffs so I was looking for some kind of a procedure to backup Docker containers and I found this link Docker backup – Easy steps to backup and restore your containers (bobcares.com) where Reeshma Mathews explained how to do it.

However, sometimes I need to perform the backup procedure over several containers at the same time, so I tried to enhance this routine to make this happen using PowerShell.

I adapted Reeshma’s steps and include them in a PowerShell script as follows:

Reeshma uses docker ps command to get the containers in the Docker environment.

However, the command do not get those containers not running at the time of command execution.

So, I use the command adding the -a parameter, which list all the containers.

The command returns the information in several columns, as space separated values.

The last column is the name of the container, so I get the information by looking of the last space (Docker do not admit spaces in the containers name, so the last space is the previous char of the container name).

I store the result in a PowerShell variable, which becomes a string array, including the titles row.

$Result=docker ps -a

So, starting at the row number one  of the array, (starting in zero), there are the values from the containers. Each row is used as an argument of a function, which performs the actions documented by Reeshma.

for($i=1;$i -lt $result.count;$i++)
{
 
    Backup-Container $result[$i]
}

However, we need to use variables instead of hardcoding the names.

Since docker commands do not interpret the parameters well when call them from PowerShell, it is needed to prepare them in a string variable and call them by Invoke-Expression PowerShell command.

	 $command="docker save -o $namebak $Name"
	 Invoke-Expression $command

This is the function where I adapted the original code:

function Backup-Container
{
[CmdletBinding()]
param
(
	[Parameter(Mandatory=$true,Position=0,HelpMessage="Must define the docker container name" )]
	[string]$Line
 
)
 
	 $SpacePos=$Line.IndexOf(' ') # Find the first space to retrieve the ContainerID
	 $ContainerID=$Line.Substring(0,$SpacePos)
	 $SpacePos=$Line.LastIndexOf(' ') # Find the last space, where starts the container's name
	 $name=$Line.Substring($SpacePos)
	 Write-host "Backing up $name"
	 $Name=$Name.ToLower()+"bkp" # Add 'bkp' the the container's name as file name for the backup
	 $command="docker commit  $ContainerID $name" # First, create a commited version of the container
	 Invoke-Expression $command
	 $namebak="$name.tar"
	 $command="docker save -o $namebak $Name" # Then, save the commited one to disk
	 Invoke-Expression $command
}

Just a final couple of comments:

  • The function is in a PowerShell module, because the idea is progressively building a library of common Docker actions. That’s why the first line is for include the library.
Import-Module -Name D:\Desarrollos\PowerShell\Docker\DockerLib.psm1
  • The script change drive and folder to establish the place where I use to store the backups. Please, adapt it to your needs.
d: cd D:\Desarrollos\Docker\Backup
  • By using the Get-Process command, the script ensures Docker Desktop is running until start the process. If it is not the case, the script starts Docker Desktop.
# Look for Docker Desktop instance
$DockerProcesses=Get-Process|Where-Object {$_.ProcessName -eq 'Docker Desktop'}
if($DockerProcesses.count -eq 0) #If there is no instance, try to start it
{
    $command="C:\Program Files\Docker\Docker\Docker Desktop.exe"
    Invoke-Expression "& '$command'"
    while($DockerProcesses.count -eq 0) #Whait for an instance
    {
        Start-Sleep -Seconds 120
        $DockerProcesses=Get-Process|Where-Object {$_.ProcessName -eq 'Docker Desktop'}
    }
}

As usual, here you have the Docker Full backup script, and here the Docker library.

HTH