Golang – building with Makefile and Jenkins

I’ve recently been working on a large Go project, and one of the deliverables was that the project be buildable using Jenkins. I was unfamiliar with Jenkins, and there didn’t seem to be any documentation around on how to build Go executables.

Project Structure

First of all an aside on project structure. For my first project I had a GOPATH of ~/go and the following directory structure:

~/go
  |--bin
  |--pkg
  |--src

But as I wrote more Go projects, it made more sense to separate each project into it’s own directory structure:

~/go
  |--project1
    |--bin
    |--pkg
    |--src
  |--project2
    |--bin
    |--pkg
    |--src

With this directory structure I set GOPATH on the command line or in a Makefile:

% cd ~go/project2/src/github.com/soniah/gosnmp
% GOPATH=~go/project2 go build

Makefile

For smaller projects you can just produce a binary using go run or go build. But a Makefile will be needed for larger projects, as they will have other deliverables besides a binary – for example manpages or an operating system installer like a .deb for Ubuntu/Debian.

GOROOT := /usr/lib/go
GOPATH := /var/lib/jenkins/workspace/go/project2

myhostname := $(shell hostname)
ifeq (${myhostname}, laptop)
    GOPATH := /home/sonia/go/project2
else ifeq (${myhostname}, testmachine)
    GOPATH := /home/u1234/go/project2
    GOROOT := /usr/local/go
endif

build: build-stamp
build-stamp: file1.go file2.go file3.go
    # always format code
    GOPATH=$(GOPATH) go fmt $^
    # binary
    GOPATH=$(GOPATH) go build -o project2 -v $^
    # docs
    markdown README.mkd > README.html
    help2man --no-info --include=help2man.roff --name "Project2" ./project2 > project2.roff
    man -Tps -l project2.roff > project2-man.ps
    ps2pdf project2-man.ps project2-man.pdf
    # mark as done
    touch $@

Jenkins

With a working Makefile, building under Jenkins will now be easier. The objective is to have Jenkins automatically build a new binary/package whenever a developer pushes to one of the git/mercurial/bzr repos that makeup the various components of your project.

However if your project contains multiple components, you’ll soon come across a problem. For example Project2 was using github.com/droundy/goopt and github.com/mattn/go-sqlite3. To see the problem, create a New Job using Build a free-style software project. Under Source Code Management, choose something like Git. Under the second Advanced button, you’ll need to change the option Local subdirectory for repo (optional) to point to the path of a component’s repo. But this setting is a global setting for all git repos – so the build won’t work as you add a second and third component.

The solution is to install to Jenkins the Multiple SCMs Plugin. Then in your Jenkins Job you’ll be able to set the local subdirectory for each component. For example in Project2:

  • the goopt local subdirectory was set to project2/src/github.com/droundy/goopt
  • the go-sqlite3 local subdirectory was set to project2/src/github.com/mattn/go-sqlite3

Other Jenkins  Settings

Here are some other useful setting for building Go projects on Jenkins:

  • if you’re building 32 and 64 bit binaries (on different build servers), use the setting Restrict where this project can be run with something like “32bit&&precise&&ubuntu”
  • separate out your Go code from other languages – Advanced Project Options, Use custom workspace, “/var/lib/jenkins/workspace/go”
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