How to add service to docker container?

Question

Is it possible to install an additional feature to a specific docker layer? In practice, I want to add the ability to handle ssh from a terminal for scripts launched by asp.net core applications. In a normal nondocker environment, this works fine.

MyDockerFile:

FROM mcr.microsoft.com/dotnet/aspnet:3.1 AS base
WORKDIR /app
FROM mcr.microsoft.com/dotnet/sdk:3.1 AS build
WORKDIR /src
COPY ["LinuxConsoleApp/LinuxConsoleApp.csproj", "LinuxConsoleApp/"]
COPY . ./
WORKDIR "/src/LinuxConsoleApp"
RUN dotnet build "LinuxConsoleApp.csproj" -c Release -o /app/build
FROM build AS publish
RUN dotnet publish "LinuxConsoleApp.csproj" -c Release -o /app/publish
FROM base AS final
WORKDIR /app

##instaling additional service, in my case ssh-client
RUN apt-get update && apt-get install -y openssh-client
##changing permissions
RUN mkdir -p /root/.ssh && \
  chmod 0700 /root/.ssh 

###unsafe coping private key to container - i know 
COPY id_rsa /root/.ssh/id_rsa

WORKDIR /app/

###here ssh can connect from docker to localhost during build time
RUN ssh -o StrictHostKeyChecking=no troom@192.168.0.200

COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "LinuxConsoleApp.dll"]
COPY LinuxConsoleApp/data /app/scripts

When i try to run script from asp.net core container i get message:

/app/scripts/Import.sh: 1: /app/scripts/Import.sh: ssh: not found

Where Import.sh is my script containg:

ssh -o StrictHostKeyChecking=no troom@192.168.0.200

As you can see, it installs the ssh client, but I don't understand why it is not available from the asp.net core application

Answer 1

The solution to the problem was not obvious, at least to me.

Long story: UTF-8 BOM https://www.w3.org/International/questions/qa-byte-order-mark

Short story: My ssh file was in a format that had invisible characters. So it was enough to create a new file, copy the contents there (in my case ssh -o StrictHostKeyChecking=no troom@192.168.0.200) and everything started to work properly.

To sum up, the above dockerfile is correct and can be safely used. The problem was the script file.