Example Dockerfile for SSH Server on Windows Server Core

dockerfile

FROM microsoft/windowsservercore:1709

# Install Powershell
ADD https://github.com/PowerShell/PowerShell/releases/download/v6.0.0/PowerShell-6.0.0-win-x64.zip c:/powershell.zip
RUN powershell.exe -Command Expand-Archive c:/powershell.zip c:/PS6 ; Remove-Item c:/powershell.zip
RUN C:/PS6/pwsh.EXE -Command C:/PS6/Install-PowerShellRemoting.ps1

# Install SSH
ADD https://github.com/PowerShell/Win32-OpenSSH/releases/download/0.0.24.0/OpenSSH-Win64.zip c:/openssh.zip
RUN c:/PS6/pwsh.exe -Command Expand-Archive c:/openssh.zip c:/ ; Remove-Item c:/openssh.zip
RUN c:/PS6/pwsh.exe -Command c:/OpenSSH-Win64/Install-SSHd.ps1

# Configure SSH
COPY sshd_config c:/OpenSSH-Win64/sshd_config
COPY sshd_banner c:/OpenSSH-Win64/sshd_banner
WORKDIR c:/OpenSSH-Win64/
# Don't use powershell as -f paramtere causes problems.
RUN c:/OpenSSH-Win64/ssh-keygen.exe -t dsa -N "" -f ssh_host_dsa_key && \
    c:/OpenSSH-Win64/ssh-keygen.exe -t rsa -N "" -f ssh_host_rsa_key && \
    c:/OpenSSH-Win64/ssh-keygen.exe -t ecdsa -N "" -f ssh_host_ecdsa_key && \
    c:/OpenSSH-Win64/ssh-keygen.exe -t ed25519 -N "" -f ssh_host_ed25519_key

# Create a user to login, as containeradministrator password is unknown
RUN net USER ssh "Passw0rd" /ADD && net localgroup "Administrators" "ssh" /ADD

# Set PS6 as default shell
RUN C:/PS6/pwsh.EXE -Command \
    New-Item -Path HKLM:\SOFTWARE -Name OpenSSH -Force; \
    New-ItemProperty -Path HKLM:\SOFTWARE\OpenSSH -Name DefaultShell -Value c:\ps6\pwsh.exe -PropertyType string -Force ; 

RUN C:/PS6/pwsh.EXE -Command \
    ./Install-sshd.ps1; \
    ./FixHostFilePermissions.ps1 -Confirm:$false;

EXPOSE 22
# For some reason SSH stops after build. So start it again when container runs.
CMD [ "c:/ps6/pwsh.exe", "-NoExit", "-Command", "Start-Service" ,"sshd" ]

sshd_banner

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=============================================================================================

* login as ssh / Passw0rd

sshd_config

Port 22

Protocol 2

LogLevel DEBUG

# Authentication:

#LoginGraceTime 2m
PermitRootLogin yes
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10

#RSAAuthentication yes
#PubkeyAuthentication yes

# The default is to check both .ssh/authorized_keys and .ssh/authorized_keys2
# but this is overridden so installations will only check .ssh/authorized_keys
AuthorizedKeysFile      .ssh/authorized_keys

# To disable tunneled clear text passwords, change to no here!
PasswordAuthentication yes
PermitEmptyPasswords yes

Banner sshd_banner

Subsystem       sftp    sftp-server.exe

hostkeyagent \\.\pipe\openssh-ssh-agent

Great work Martin et al, thanks ever so much. This is really helpful. Love the banner!

For applications that only require Powershell 5.1, I've been able to produce a much simpler Dockerfile, based on these commands:
https://learn.microsoft.com/en-us/windows-server/administration/openssh/openssh_install_firstuse?tabs=powershell
I've got it to run based on a servercore:ltsc2022 image, and carried out a basic test of it within a Github Actions windows-2022 runner (sshing from a different process in the job using Python & Fabric). FYI there are official Powershell images now to use, if you do want a later Powershell version. You just need to figure out the path to powershell.exe if you want it as the log in shell - the docker files are on Github.

# escape=`

FROM mcr.microsoft.com/windows/servercore:ltsc2022
# hadolint shell=powershell

USER ContainerAdministrator

SHELL ["cmd.exe", "/C"]

RUN net USER ssh "Passw0rd" /ADD && net localgroup "Administrators" "ssh" /ADD

SHELL ["powershell", "-Command", "$ErrorActionPreference = 'Stop'; $ProgressPreference = 'SilentlyContinue';"]

RUN New-ItemProperty -Path "HKLM:\SOFTWARE\OpenSSH" -Name DefaultShell -Value "C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe" -PropertyType String -Force

RUN Add-WindowsCapability -Online -Name OpenSSH.Server~~~~0.0.1.0; `
    Start-Service sshd; `
    Set-Service -Name sshd -StartupType 'Automatic'

EXPOSE 22

# Ping self to keep container alive
CMD ["cmd.exe", "/c", "ping", "-t", "localhost", ">", "NUL"]

The same Dockerfile with more comments, a Github Action workflow, a Python test script, and test results are in this repo:
https://github.com/JamesParrott/Windows__ssh_server_with_powershell/