Deploying .NET applications with the Nix package manager

Deploying .NET applications with the Nix package
manager
Sander van der Burg
Delft University of Technology, EEMCS,
Department of Software Technology
Philips Healthcare, Philips Informatics Infrastructure (PII),
Best
June 15, 2010
Sander van der Burg Deploying .NET applications with the Nix package manager

Nix deployment system
Nix is a package manager, with some distinct features:
Stores components in isolation from each other
Allows using multiple variants/versions safely next to each
other
Builds components from declarative speciﬁcations
Reproducibility
Supports atomic upgrades and rollbacks
Garbage collection
Safely removes obsolete components

Nix deployment system
About 2500 open-source/free software packages are supported
(Nixpkgs)
Used as a basis for the NixOS GNU/Linux distribution

Hydra
Continuous build & integration server
Built upon the Nix package manager
Used at TU Delft for building, integration and testing of
several projects on multiple platforms

Disnix
Distributed deployment extension for Nix
Manages inter-dependencies
Builds, distributes, activates services in a network of machines

The Nix store
All components are stored in isolation in a Nix store
In Nix every component name consists of a hash code and
component name:
/nix/store/30v58jznlaxnr4bca3hiz64wlb43mgpx-hello-2.5
Hash is generated from all the input arguments of the build
function: compilers, libraries, build scripts etc.
Multiple variants/versions can be kept safely next to each
other
Can be used for any type of component

The Nix store
/nix/store
44ef921582e840dae...-glibc-2.9
lib
libc.so
a1v58jz2la6nr7bcr...-glibc-2.11.1
lib
libc.so
30v58jznlaxnr4bca...-hello-2.5
bin
hello
0a4d829298227c98c...-hello-2.5
bin
hello

Global Assembly Cache (GAC)
.NET Global Assembly Cache (GAC) only supports strong-named
library assemblies (DLLs):
Other types of components are not supported (executables,
native DLLs, compilers)
Strong name is created from name, version, culture and
signing with a public-private key pair
Creating strong-names is sometimes painful
Possible to produce a diﬀerent assembly with same
strong-name

Nix expressions
{stdenv, fetchurl}:
stdenv.mkDerivation {
name = "hello-2.5";
src = fetchurl {
url = ftp://ftp.gnu.org/gnu/hello/hello-2.5.tar.gz;
sha256 = "0in467phypnis2ify1gkmvc5l2fxyz3s4xss7g74gwk279ylm4r2";
};
meta = {
description = "A program that produces a familiar, friendly greeting";
homepage = http://www.gnu.org/software/hello/manual/;
license = "GPLv3+";
};
}
Speciﬁes how the hello component should be built.

Nix expressions
rec {
stdenv = ...
curl = ...
openssl = ...
fetchurl = import ../build-support/fetchurl {
inherit curl openssl;
};
hello = import ../applications/misc/hello {
inherit stdenv fetchurl;
};
}
The hello build function is called with its arguments

Nix expressions
To build the Hello package:
$ nix-build all-packages.nix -A hello
Will recursively build hello and its dependencies and produces hello
in:
/nix/store/30v58jznlaxnr4bca3hiz64wlb43mgpx-hello-2.5

Runtime dependencies
Nix detects runtime dependencies of a build
Nix scans all files of a component for hash-codes of a
dependency, e.g. RPATH defined in a ELF header
Uses a notion of closures to guarantee completeness:
If a specific component needs to be deployed, all its runtime
dependencies are deployed first

Runtime dependencies
/nix/store
44ef921582e840dae...-glibc-2.9
lib
libc.so
a1v58jz2la6nr7bcr...-glibc-2.11.1
lib
libc.so
30v58jznlaxnr4bca...-hello-2.5
bin
hello
0a4d829298227c98c...-hello-2.5
bin
hello

Supporting .NET applications with Nix
Nix is designed for use on UNIX like systems, e.g. GNU/Linux,
FreeBSD, Mac OS X

Requirements
Buildtime support:
Compile Visual Studio solutions and produce assemblies
Invoke MSBuild.exe with right parameters
The build process must ﬁnd its buildtime dependencies
Runtime support:
Assemblies must ﬁnd its runtime dependencies
Integrate .NET CLR dependency resolver with Nix

Windows support
Nix is supported on Windows through Cygwin:
Oﬀers UNIX implementation on top of Windows
Allows combining UNIX and Windows utilities

Windows support
Several Cygwin utilities map Windows concepts to UNIX concepts
and vica versa:
Can be used to glue UNIX tooling to Windows processes
cygpath, UNIX path names <=> Windows path names

Implementing build support
A .NET Nix build function dotnetenv.buildSolution is
implemented:
Takes source code of a Visual Studio C# solution
Produces output of the solution into a unique store path,
based on the input arguments of this function

Build function implementation
{stdenv, dotnetfx}:
{ name, src, slnFile, targets ? "ReBuild"
, options ? "/p:Configuration=Debug;Platform=Win32"
, assemblyInputs ? []
}:
stdenv.mkDerivation {
inherit name src;
buildInputs = [ dotnetfx ];
installPhase = ’’
for i in ${toString assemblyInputs}; do
windowsPath=$(cygpath --windows $i)
AssemblySearchPaths="$AssemblySearchPaths;$windowsPath"
done
export AssemblySearchPaths
ensureDir $out
outPath=$(cygpath --windows $out)
MSBuild.exe ${slnFile} /nologo /t:${targets}
/p:OutputPath=$outPath ${options} ...
’’;
}

Example usage
{dotnetenv, MyAssembly1, MyAssembly2}:
dotnetenv.buildSolution {
name = "My.Test.Assembly";
src = /path/to/source/code;
slnFile = "Assembly.sln";
assemblyInputs = [
dotnetenv.assembly20Path
MyAssembly1
MyAssembly2
];
}
Speciﬁes how a Visual Studio solution should be built.

Example usage
rec {
dotnetfx = ...
stdenv = ...
dotnetenv = import ../dotnetenv {
inherit stdenv dotnetfx;
};
MyAssembly1 = import ../MyAssembly1 {
inherit dotnetenv;
};
MyAssembly2 = import ../MyAssembly1 {
inherit dotnetenv;
};
MyTestAssembly = import ../MyTestAssembly {
inherit dotnetenv MyAssembly1 MyAssembly2;
};
}
The MyTestAssembly function is called with its arguments

Example usage
To build the My.Test.Assembly component:
$ nix-build all-packages.nix -A MyTestAssembly
Recursively builds My.Test.Assembly and its dependencies, i.e.
MyAssembly1, MyAssembly2, MyTestAssembly and produces
output in:
/nix/store/ri0zzm2hmwg01w2wi0g4a3rnp0z24r8p-My.Test.Assembly

Implementing runtime support
.NET runtime locaties assemblies:
Determines the correct version of the assembly (strong-named
assemblies only)
Checks whether the assembly has been bound before
(strong-named assemblies only)
If so, it uses this version
Shares same assemblies in memory between applications
Checks the Global Assembly Cache (GAC) (strong-named
assemblies only)
Probes the assembly
Checking the <codebase> element in the application .config
Probing heuristics

Assembly probing
A <codebase> element in the application .config ﬁle can specify
its own assembly references:
Private assemblies can only reside in the directory or a
subdirectory of the executable
Strong-named assemblies can be invoked from an arbitrary
location, including remote locations
Referenced assembly is cached, therefore a strong-name is
required

Implementing runtime support in Nix
Not very trivial, 3 options:
Copy dependent assemblies into the same Nix store path as
the executable
Generate an application .config ﬁle with <codebase>
section
Symlink dependent assemblies into the same Nix store path as
the executable

Copy dependent assemblies
Copy dependent assemblies into the same Nix store path as the
executable:
Essentially static linking
Expensive in terms of disk space
Expensive in terms of memory usage
Works with private and strong-named assemblies
Works on Windows 2000, XP

Copy dependent assemblies
/nix/store
99bed1970e5e459bc...-My.Assembly1
My.Assembly1.dll
f4e5d4c96f95c5887...-My.Assembly2
My.Assembly2.dll
ri0zzm2hmwg01w2wi...-My.Test.Assembly
My.Assembly1.dll
My.Assembly2.dll
My.Test.Assembly.exe

Generate an application config file
Generate an application config file with <codebase> section:
References assemblies in other Nix store paths
Nix scans and detects runtime dependencies due to unique
store paths
Cheap in terms of disk space
Allows efficient upgrading of a system (i.e. only replacing
updated parts)
Only works with strong-named assemblies
Cheap in terms of memory usage (sharing in memory)

Generate an application conﬁg ﬁle
/nix/store
My.Assembly1.dll
My.Assembly2.dll
My.Test.Assembly.exe.config

Symlink dependent assemblies
Symlink dependent assemblies into the same Nix store path as the
executable:
References assemblies in other Nix store paths
Nix scans and detects runtime dependencies due to unique
store paths
Cheap in terms of disk space
Works with private and strong-named assemblies
Allows eﬃcient upgrading of a system (i.e. only replacing
updated parts)
Expensive in terms of memory usage (no sharing)
NTFS symlinks are only supported in Windows Vista+,
Windows Server 2008+

Symlink dependent assemblies
/nix/store
My.Assembly1.dll
My.Assembly2.dll
My.Assembly1.dll
My.Assembly2.dll

Result
With this implementation we can build and run .NET software
with Nix, some caveats:
.NET framework and Visual Studio tools are not managed by
Nix
.NET framework has dependencies which must be in the GAC
and registry
Registry is not managed
Do not use of registry for conﬁguration settings
Some UNIX properties are not enforced when invoking native
Windows processes:
e.g. chroot
Makes it slightly harder to guarantee purity

Possible applications
Use Nix for deployment of .NET applications
Oﬀers the beneﬁts of Nix (e.g. atomic upgrading) for .NET
applications
Allows the deployment of complete systems
No need to create your own installers
Hydra, http://nixos.org/hydra
Continuous integration & testing of .NET applications
Build and test components for multiple architectures
Disnix, http://nixos.org/disnix
Distributed deployment of .NET services into a network of
machines

References
Nix, Nixpkgs, Hydra, NixOS, Disnix, http://nixos.org
Cygwin, http://www.cygwin.com
Demystifying the .NET Global Assembly Cache, http:
//www.codeproject.com/kb/dotnet/demystifygac.aspx
Common MSBuild Project Properties, http:
//msdn.microsoft.com/en-us/library/bb629394.aspx

References
How the Runtime Locates Assemblies,
http://msdn.microsoft.com/en-us/library/yx7xezcf%
28VS.71%29.aspx
Locating the Assembly through Codebases or Probing,
http://msdn.microsoft.com/en-us/library/15hyw9x3%
28VS.71%29.aspx
Assembly Searching Sequence, http://msdn.microsoft.
com/en-us/library/aa374224%28VS.85%29.aspx

Questions

Deploying .NET applications with the Nix package manager

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