NuGet with Docker Builds

A Docker build does not necessarily run in a context that is authorised to access a private NuGet feed, so we have a challenge to access our packages on a dotnet restore.

We can pass credentials via a NuGet.config file, but we don’t really want to store these in Source Control.

First of all, we add NuGet.config to our .gitignore file (or whatever your source control uses to exclude files)

Next we head on over to Azure DevOps to create a personal access token

The only scope you need is “Packaging (Read)”, which only allows access to pull NuGet packages.

Now we need to create a relevant entry in our root NuGet.config file. On Windows, this is located at %appdata%\NuGet\NuGet.Config

<packageSources>
  <add key="((myfeedname))" value="((myfeedurl))" />
</packageSource>

...

<packageSourceCredentials>
  <((myfeedname))>
    <add key="Username" value="anything" />
    <add key="ClearTextPassword" value="((my-personal-access-token))" />
  </((myfeedname))>
</packageSourceCredentials>

We can now write a PowerShell script to pull this in to our working directory before each Docker build (I’m using Docker Compose here)

copy $env:APPDATA\NuGet\NuGet.Config NuGet.Config
docker-compose build

I save this next to my docker-compose.yml.

The final step is to use the dockerfile to tell the Docker build to pull in our generated configuration

COPY NuGet.config ((folder containing my .csproj or .sln))/

Now when I run the PowerShell script I will get a fresh copy of my NuGet.config from a single source, and it is never checked into source control.

When building on the Build server, I recommend using a different access token, storing it as a secret and generating the NuGet.config on the fly as a build step, e.g.

echo '<?xml version="1.0" encoding="utf-8"?><configuration><packageSources><add key="MyFeed" value="$(NuGet-Feed)" /></packageSources><packageSourceCredentials><MyFeed><add key="Username" value="Anything" /><add key="ClearTextPassword" value="$(NuGet-PAT)" /></MyFeed></packageSourceCredentials></configuration>' > NuGet.config