# Container with build environment¶

Note

Sometimes we encounter applications that have system dependencies which are incompatible with the global environment on the cluster. This can happen for instance if you download a precompiled binary from an online archive which has been built for a specific OS version or depends on a system library which is not available, or if you want to compile your own application with some non-standard dependencies. One way to resolve such issues is to containerize the appropriate environment and run/compile your application through this container on the cluster. In the following examples we will demonstrate such a work flow.

## Hello world example¶

This example demonstrates:

1. how to write a simple Singularity definition file

2. how to install system packages on top of a standard OS base image

3. how to build the container on your laptop

4. how to run commands through the container environment on the cluster

In this example we will create a very simple container environment with a Ubuntu-16.04 operating system and a GNU compiler. We will then use this environment to compile a simple program on the cluster.

Writing the definition file

We start with the following definition file (we call it example.def)

Bootstrap: docker
From: ubuntu16.04

%post
apt-get update && apt-get install -y g++


This recipe will pull the ubuntu16.04 image from the docker registry and install the GNU C++ compiler using the Ubuntu package manager. Any system package that is available for the base OS can be installed in this way. Other common Bootstrap options include library for the Singularity Container Library, shub for Singularity-Hub or localimage if you want to build on top of another image located on your computer.

Tip

You can find much more on Singularity definition files here.

Building the container

We can now build the container with the following command (you need sudo rights for this step):

[me@laptop]$sudo singularity build example.sif example.def [... lots of output ...] INFO: Adding environment to container INFO: Creating SIF file... INFO: Build complete: example.sif  Running the container Once example.sif is generated, we can scp the container file to the cluster: [me@laptop]$ scp example.sif me@saga.sigma2.no


First we check the default g++ compiler on the cluster:

[me@login-1.SAGA ~]$g++ --version g++ (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44) Copyright (C) 2015 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  Then we check the g++ version in the container by running the command through singularity exec: [me@login-1.SAGA ~]$ singularity exec example.sif g++ --version
g++ (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


We write a simple hello-world.cpp program:

#include <iostream>

int main() {
std::cout << "Hello World!" << std::endl;
return 0;
}


and compile it through the container environment:

[me@login-1.SAGA ~]$singularity exec example.sif g++ hello-world.cpp [me@login-1.SAGA ~]$ singularity exec example.sif ./a.out
Hello World!


Remember that you also need to run the program through the container if it is dynamically linked to some of the containerized libraries.

## Real world example: pdflatex¶

This example demonstrates:

1. how to build a container from a definition file

2. how to set environment variables inside the container

3. how to document your container

4. how to make your container look like an executable application

5. how to run your container application on the cluster

Latex is a software package with a plethora of different package options which can easily mess up your global environment. It is something that is typically not installed on compute clusters, but could still be useful e.g. for building code documentation. In this example we will create a fully functional container for the pdflatex command for building PDFs from tex files.

Writing the definition file

Bootstrap: library
From: ubuntu:20.04

%post
apt-get install -y software-properties-common
apt-get update -y
apt-get install -y texlive texlive-fonts-extra

%environment
export LC_ALL=C

%runscript
pdflatex $@ %labels Author Me <me@mymail.com> Description PDF latex on a Ubuntu-20.04 base image Version v1.0.0 %help How to run the container on a tex file:$ ./<image-name>.sif <file-name>.tex


Here we use the Ubuntu package manager to install a few texlive packages on top of a Ubuntu-20.04 base image, and we set the LC_ALL environment variable inside the container at run time. The %runscript section specifies the commands to be run inside the container when you launch the image file as an executable, where the $@ will capture an argument string. In this particular example it means that we can run the image as $ ./<image-name>.sif <file-name>.tex


which will be equivalent of running the given %runscript command (pdflatex in this case) through the container with singularity exec:

$singularity exec <image-name>.sif pdflatex <file-name>.tex  Finally, we add a few labels (accessible through singularity inspect <image-name>.sif) and a help string (accessible through singularity run-help <image-name>.sif) for documentation. Building the container We build the container on a local computer (requires sudo rights), where we have called the definition and image files pdflatex.def and pdflatex.sif, respectively: [me@laptop]$ sudo singularity build pdflatex.sif pdflatex.def

[... lots of output ...]

This may take some time... done.
INFO:    Creating SIF file...
INFO:    Build complete: pdflatex.sif


Inpecting the container

When the image is ready we can inspect the metadata that we put into it

[me@laptop]$singularity inspect pdflatex.sif Author: Me <me@mymail.com> Description: PDF latex on a Ubuntu-20.04 base image Version: v1.0.0 org.label-schema.build-arch: amd64 org.label-schema.build-date: Thursday_10_June_2021_13:12:27_CEST org.label-schema.schema-version: 1.0 org.label-schema.usage: /.singularity.d/runscript.help org.label-schema.usage.singularity.deffile.bootstrap: library org.label-schema.usage.singularity.deffile.from: ubuntu:20.04 org.label-schema.usage.singularity.deffile.mirrorurl: http://us.archive.ubuntu.com/ubuntu/ org.label-schema.usage.singularity.deffile.osversion: focal org.label-schema.usage.singularity.runscript.help: /.singularity.d/runscript.help org.label-schema.usage.singularity.version: 3.7.0  [me@laptop]$ singularity run-help pdflatex.sif
How to run the container on a tex file:
$./<image-name>.sif <file-name>.tex  Running the container When we are happy with the container we can move it to any machine where we would like to run pdflatex. Here we scp to Saga and log in with -X in order to browse the produced PDF: [me@laptop]$ scp pdflatex.sif me@saga.sigma2.no
[me@laptop]$ssh -X me@saga.sigma2.no  We write a simple hello-world.tex file \documentclass[12pt]{article} \begin{document} Hello World! \end{document}  and run our container on it: [me@login-1.SAGA ~]$ ./pdflatex.sif hello-world.tex
This is pdfTeX, Version 3.14159265-2.6-1.40.20 (TeX Live 2019/Debian) (preloaded format=pdflatex) restricted \write18 enabled.
entering extended mode
(./hello-world.tex
LaTeX2e <2020-02-02> patch level 2
L3 programming layer <2020-02-14>
(/usr/share/texlive/texmf-dist/tex/latex/base/article.cls
Document Class: article 2019/12/20 v1.4l Standard LaTeX document class
(/usr/share/texlive/texmf-dist/tex/latex/base/size12.clo))
(/usr/share/texlive/texmf-dist/tex/latex/l3backend/l3backend-pdfmode.def)
No file hello-world.aux.
[1{/var/lib/texmf/fonts/map/pdftex/updmap/pdftex.map}] (./hello-world.aux) )</u
sr/share/texlive/texmf-dist/fonts/type1/public/amsfonts/cm/cmr12.pfb>
Output written on hello-world.pdf (1 page, 9893 bytes).
Transcript written on hello-world.log.


Finally, you can inspect the produced file e.g. in a browser:

[me@login-1.SAGA ~]\$ firefox hello-world.pdf


where you will hopefully see an almost blank page with the words “Hello World!” written.