Program does not contain a static 'Main' method suitable for an entry point

[xiaotupansy]

Hi,
Environment :
Centos 7.3
Docker version 17.09.0-ce, build afdb6d4
microsoft/aspnetcore-build docker image, pulled just now using docker pull microsoft/aspnetcore-build

I have two projects in solution.

demo.csproj default asp.net mvc project set up by vs 2017 community
Library.csproj default library project set up by vs 2017 community

Demo project reference the Library project.

Here is my dockerfile:

---

FROM microsoft/aspnetcore-build AS builder
WORKDIR /sln
COPY ./demo.sln  ./
COPY ./demo/demo.csproj  ./demo/demo.csproj
COPY ./Library/Library.csproj  ./Library/Library.csproj

RUN dotnet restore
RUN dotnet build -c Release --no-restore

RUN dotnet publish "./demo/demo.csproj" -c Release -o "../dist" --no-restore

FROM microsoft/aspnetcore
WORKDIR /app
COPY --from=builder /sln/dist .
ENTRYPOINT ["dotnet", "demo.dll"]

---

Here is my docker command:

docker build /site/test -t aspnetapp

Here is the output:

[root@worth ~]# docker build /site/test -t aspnetapp
Sending build context to Docker daemon  5.083MB
Step 1/12 : FROM microsoft/aspnetcore-build AS builder
 ---> 244f6193d21a
Step 2/12 : WORKDIR /sln
 ---> Using cache
 ---> 44b558ba58b0
Step 3/12 : COPY ./demo.sln ./
 ---> 7dfd84d431b9
Step 4/12 : COPY ./demo/demo.csproj ./demo/demo.csproj
 ---> e8e751c2bca7
Step 5/12 : COPY ./Library/Library.csproj ./Library/Library.csproj
 ---> b0a979746fdf
Step 6/12 : RUN dotnet restore
 ---> Running in 5dabe8ff613f
  Restoring packages for /sln/Library/Library.csproj...
  Restoring packages for /sln/demo/demo.csproj...
  Generating MSBuild file /sln/Library/obj/Library.csproj.nuget.g.props.
  Generating MSBuild file /sln/Library/obj/Library.csproj.nuget.g.targets.
  Restore completed in 718.77 ms for /sln/Library/Library.csproj.
  Restoring packages for /sln/demo/demo.csproj...
  Restore completed in 3.46 sec for /sln/demo/demo.csproj.
  Generating MSBuild file /sln/demo/obj/demo.csproj.nuget.g.props.
  Generating MSBuild file /sln/demo/obj/demo.csproj.nuget.g.targets.
  Restore completed in 5.91 sec for /sln/demo/demo.csproj.
 ---> 75c5eb8d871e
Removing intermediate container 5dabe8ff613f
Step 7/12 : RUN dotnet build -c Release --no-restore
 ---> Running in 40ee491a3603
Microsoft (R) Build Engine version 15.6.82.30579 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Library -> /sln/Library/bin/Release/netcoreapp2.0/Library.dll
CSC : error CS5001: Program does not contain a static 'Main' method suitable for an entry point [/sln/demo/demo.csproj]

Build FAILED.

CSC : error CS5001: Program does not contain a static 'Main' method suitable for an entry point [/sln/demo/demo.csproj]
    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:06.10
The command '/bin/sh -c dotnet build -c Release --no-restore' returned a non-zero code: 1

[natemcmaster]

This error isn't specific to Docker. It's a C# compiler error. For any project that is <OutputType>exe</OutputType>, you need to have a method like this public static void Main(string[] args) somewhere in your project.

[xiaotupansy]

Here is the output from centos without docker using the same code:

[root@localhost ~]# dotnet build -c release /site/test1/demo/demo.sln
Microsoft (R) Build Engine version 15.3.409.57025 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Library -> /site/test1/demo/Library/bin/Release/netcoreapp2.0/Library.dll
  demo -> /site/test1/demo/demo/bin/Release/netcoreapp2.0/demo.dll

Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:25.02
[root@localhost ~]#

So I think maybe something wrong in build image.

I did a lot of searching before I post this issue. I'm sure code can work both in iisexpress and kestrel.

[natemcmaster]

If you can provide exact steps to reproduce the issue, we may be able to investigate more. The error message indicates that you are missing some of your source code when building inside the container. Double check your COPY statements in your Dockerfile. Not trying to be mean -- we just don't have enough info to investigate, so I closed it because we are not planning on taking action here.

[natemcmaster]

...and of course, I see you edited the original issue. So far you've only copied your .csproj files into the container. You need the .cs files too. Add this line to your dockerfile before dotnet build to copy everything.

COPY . .

[xiaotupansy]

Thanks.
After copy files, it works now.

[lcr0815]

what is the exact meaning of COPY . .

[natemcmaster]

Syntax for this directive is COPY <src> <dest>. This is the same as COPY ./ ./. See https://docs.docker.com/engine/reference/builder/#copy

[Rickinio]

Hi, i had the exact same error message and for me the issue was that i had my Docker file at the same level as my .csproj. When i moved csproj one level deeper, docker build run successfully.

[lawphotog]

Got the same issue and what Rickinio said was right. Once I moved the Docker file one level up, things look better. But why was the file at the same level from the first place. I just created a fresh app. I guess they had to put at the same level so that Dockerfile is included in the solution explorer for those who use Visual Studio. VS seems smart enough to find things and start docker but docker build command wasn't working unless i moved the Dockerfile.

[Teklie]

This error isn't specific to Docker. It's a C# compiler error. For any project that is <OutputType>exe</OutputType>, you need to have a method like this public static void Main(string[] args) somewhere in your project.

Thanks. It worked.

[davidebbo]

I ran into the same thing. There seems to be a VS bug here causing it to create the Dockerfile in the wrong place.

[cilliemalan]

I randomly got this issue when I was (accidentally) building to a parent directory. Like so:

WORKDIR /app/src/
RUN dotnet build Thing.csproj -c Release -o /app

Fixed it by chainging /app to /out