Unable to load assembly in container environment

I have a .Net 2.2 core application that I’m trying to move into a container and I’m having little success getting the assembly loaded. I’m curious has anyone attempted this with any success? I have been hung up on an ELF header error for two days now :

“System.DllNotFoundException: Unable to load shared library ‘/app/libwkhtmltox.dll’ or one of its dependencies. In order to help diagnose loading problems, consider setting the LD_DEBUG environment variable: /app/libwkhtmltox.dll: invalid ELF header”

Details :

1. Its a 64-bit container image (Debian 9). It’s worth pointing out I’m currently using microsoft/dotnet:2.2-aspnetcore-runtime and I have tried :

   • mcr.microsoft.com/dotnet/core/runtime:2.2
   • mcr.microsoft.com/dotnet/core/runtime:2.2-stretch-slim
   • mcr.microsoft.com/dotnet/core/runtime:2.2-bionic
   • mcr.microsoft.com/dotnet/core/runtime:2.2.7-bionic

2. The app is built/published on the same flavor of Linux

3. The 64-bit DLL is in the apps working directory as is the dylib and so (see the file sizes in my screenshot)

4. libgdiplus is already present on the Debian 9 base image (it’s in my Dockerfile regardless)

5. I’m installing all of the dependencies I could find in the various older issues…

   • libx11-6
   • libxext6
   • libxrender1
   • zlib1g
   • fontconfig
   • libfreetype6
   • libgdiplus
   • libxcb1
   • xfonts-75dpi
   • xfonts-base

6. The Deb package for wkhtmltox is being installed.

7. libwkhtmltox.dll is also copied into /usr/lib.

I think the above covers every fix i have found on past issues for loading the dll on ubuntu and container environments, although I want to say none of those were 2.2Core

The relevant part of the C# looks like so :

        private SynchronizedConverter Converter
        {
            get
            {
                if (_converter == null)
                {
                    var context = new CustomAssemblyLoadContext();
                    var wkHtmlToPdfPath = Path.Combine(AppContext.BaseDirectory, $@"libwkhtmltox.dll");
                    Console.WriteLine($"Path to the file : {wkHtmlToPdfPath}");
                    try
                    {
                        context.LoadUnmanagedLibrary(wkHtmlToPdfPath);
                    }
                    catch (Exception e)
                    {
                        Console.WriteLine("This is where the trouble starts...");
                        Console.WriteLine(e.ToString());
                        Console.WriteLine(e.InnerException.Message.ToString());
                    }

                    _converter = new SynchronizedConverter(new PdfTools());
                }

                return _converter;
            }
        }

Which of course throws an exception :

Loaded ‘/app/DinkToPdf.dll’. Cannot find or open the PDB file. Path to the file : /app/libwkhtmltox.dll This is where the trouble starts… Loaded ‘/usr/share/dotnet/shared/Microsoft.NETCore.App/2.2.7/System.IO.MemoryMappedFiles.dll’. Skipped loading symbols. Module is optimized and the debugger option ‘Just My Code’ is enabled. System.DllNotFoundException: Unable to load shared library ‘/app/libwkhtmltox.dll’ or one of its dependencies. In order to help diagnose loading problems, consider setting the LD_DEBUG environment variable: /app/libwkhtmltox.dll: invalid ELF header at System.Runtime.Loader.AssemblyLoadContext.InternalLoadUnmanagedDllFromPath(String unmanagedDllPath) at System.Runtime.Loader.AssemblyLoadContext.LoadUnmanagedDllFromPath(String unmanagedDllPath) at FormsService.ServiceInterface.Common.HTMLToPDFConverter.get_Converter() in /src/FormsService.ServiceInterface/Common/IHTMLToPDFConverter.cs:line 21

My Dockerfile, which has gone through countless permutations over the last 12 hours or so now looks like :

FROM microsoft/dotnet:2.2-aspnetcore-runtime AS base
WORKDIR /app
EXPOSE 51950
EXPOSE 44378

FROM microsoft/dotnet:2.2-sdk AS build
WORKDIR /src
COPY ["FormsService/FormsService.csproj", "FormsService/"]
COPY ["FormsService.ServiceModel/FormsService.ServiceModel.csproj", "FormsService.ServiceModel/"]
COPY ["FormsService.ServiceInterface/FormsService.ServiceInterface.csproj", "FormsService.ServiceInterface/"]
RUN dotnet restore "FormsService/FormsService.csproj"
COPY . .
WORKDIR "/src/FormsService"
RUN dotnet build "FormsService.csproj" -c Release -o /app

FROM build AS publish
RUN dotnet publish "FormsService.csproj" -c Release -o /app

FROM base AS final
WORKDIR /app
COPY --from=publish /app .
RUN apt-get update \ 
	&& apt-get install -y zlib1g fontconfig libfreetype6 \
        libx11-6 libxext6 libxrender1 \
		libgdiplus libxcb1 xfonts-75dpi \
		xfonts-base wget \
    && wget -nv -O /tmp/wkhtmltox.deb https://downloads.wkhtmltopdf.org/0.12/0.12.5/wkhtmltox_0.12.5-1.stretch_amd64.deb \
	&& apt-get -qy install /tmp/wkhtmltox.deb \
	&& cp /usr/local/bin/wkhtmlto* /usr/bin/ \
    && curl -o /usr/lib/libwkhtmltox.so \
        --location \
        https://github.com/rdvojmoc/DinkToPdf/blob/master/v0.12.4/64%20bit/libwkhtmltox.so?raw=true \
	&& curl -o /usr/lib/libwkhtmltox.dylib \
        --location \
        https://github.com/rdvojmoc/DinkToPdf/blob/master/v0.12.4/64%20bit/libwkhtmltox.dylib?raw=true \
	&& curl -o /usr/lib/libwkhtmltox.dll \
        --location \
        https://github.com/rdvojmoc/DinkToPdf/blob/master/v0.12.4/64%20bit/libwkhtmltox.dll?raw=true \
	&& cp /usr/lib/libwkhtmltox* /app \
	&& cp /usr/lib/libwkhtmltox* /app/Dependencies/64Bit/
	

ENTRYPOINT ["dotnet", "FormsService.dll"]

I added the steps to re-download the Dll/So/Dylib on the off chance that I had some corrupt version locally. Alas this had no effect…

Does anyone have any insight into what the underlying issue maybe? I’m assuming the ELF Header is signaling that a dependency is missing or that dependency is the incorrect arch (32-bit) but I’m grasping at straws at this point.

[oscartorres9]

I have the exactly same error on centos 7,which working nicely in loacl windows 10, but occur the error when I publish my app to the centos 7 server. please tell me how to solve this fxxking problem… thanks

[mKay00]

What worked for me was to install wkhtmltopdf with apt (worked on ubuntu, but resulted in a big docker image) or use the correct binary from here, download with wget, install the .deb file with dpkg, which results in an error and then use apt-get -f install -y to correctly install it.

Here is my dockerfile to build and deploy an asp.net core app to heroku which uses wkhtmltopdf (the images used are based on debian 10):

# NuGet restore
FROM mcr.microsoft.com/dotnet/core/sdk:3.1 AS build
WORKDIR /src
COPY ["{your_solution}/{your_project}.csproj", "{your_project}/"]
RUN dotnet restore "{your_project}/{your_project}.csproj"
COPY . .

# publish
WORKDIR "/src/{your_project}"
RUN dotnet publish "{your_project}.csproj" -c Release -o /app/publish

# release
FROM mcr.microsoft.com/dotnet/core/aspnet:3.1 AS release_base
WORKDIR /tmp
# Add wkhtmltopdf and its depoendencies
RUN apt-get update \
    && apt-get install -y wget \
    && wget https://github.com/wkhtmltopdf/packaging/releases/download/0.12.6-1/wkhtmltox_0.12.6-1.buster_amd64.deb \
    && dpkg -i ./wkhtmltox_0.12.6-1.buster_amd64.deb \
    ; apt-get -f install -y \
    && rm wkhtmltox_0.12.6-1.buster_amd64.deb \
    && rm -rf /var/cache/apt/lists/*

FROM release_base AS release
WORKDIR /app
COPY --from=build /app/publish .

# Run the image as a non-root user
RUN useradd -m myuser
USER myuser

# heroku uses the following
CMD ASPNETCORE_URLS=http://*:$PORT dotnet {your_project}.dll