Fixing "pull access denied" Docker Build Errors

When building Docker images, you may encounter "pull access denied" or "insufficient_scope: authorization failed" errors. These can occur for various reasons, from authentication issues to incorrect image references and platform mismatches.

Problem Analysis

The error typically appears when Docker cannot access the specified image or repository:

failed to load cache key: pull access denied, repository does not exist or may require authorization: server message: insufficient_scope: authorization failed

This can happen when:

1. Referencing non-existent stages in multi-stage builds
2. Using incorrect image names or repositories
3. Facing authentication/authorization issues
4. Encountering platform architecture mismatches

Solutions

1. Fix Multi-Stage Build References

The most common cause is incorrect stage references in multi-stage Dockerfiles. In the provided Dockerfile, the issue is:

# Incorrect - references non-existent stage "publish/app"
COPY --from=publish/app /app .

The correct approach references an existing build stage:

# Correct - references the "build" stage that exists
COPY --from=build /app .

Complete Fixed Dockerfile

FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-buster-slim AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443

FROM mcr.microsoft.com/dotnet/core/sdk:3.1-buster AS build
WORKDIR /src
COPY ["src/App.Web/App.Web.csproj", "src/App.Web/"]
RUN dotnet restore "App.Web.csproj"
COPY . .
WORKDIR "/src/App.Web"
RUN dotnet build App.Web.csproj -c Debug -o /app

FROM build as debug
RUN dotnet publish "App.Web.csproj" -c Debug -o /app

FROM base as final
WORKDIR /app
# Fixed: references existing "build" stage instead of "publish/app"
COPY --from=build /app .
ENTRYPOINT ["dotnet","App.Web.dll"]

2. Update Outdated Image References

Microsoft has renamed many of their .NET Docker repositories. Update outdated references:

# Old (may cause issues)
FROM mcr.microsoft.com/dotnet/core/aspnet:3.1-buster-slim

# Updated (recommended)
FROM mcr.microsoft.com/dotnet/aspnet:3.1-buster-slim

3. Handle Platform Architecture Mismatches

If you're on a different architecture (like Apple Silicon M1/M2), explicitly specify the platform:

docker build . --platform linux/amd64

This forces Docker to pull the correct architecture version of base images.

4. Verify Docker Authentication

Ensure you're authenticated with the appropriate registry:

docker login

Then retry your build command:

docker build .

Best Practices

TIP

• Always verify stage names match exactly between FROM and COPY --from statements
• Use official, up-to-date image references from verified sources
• Consider platform compatibility when building across different systems
• Regularly update your Dockerfiles as repositories and image names change

Troubleshooting Steps

1. Check stage names: Ensure all COPY --from statements reference valid build stages
2. Verify image availability: Test pulling base images directly with docker pull
3. Review repository URLs: Confirm image repositories haven't been renamed or moved
4. Check platform compatibility: Use --platform flag if building across different architectures

By addressing these common issues, you can resolve "pull access denied" errors and successfully build your Docker images.