Nobody Cares About Your Build

Every software system, from simple Python packages to huge enterprise-grade +systems spanning massive clusters, has a build—a set of steps that must be +followed to go from a source tree or a checked-out project to a ready-to-use +build product. A build system's job is to automate these steps.

Build systems are critical to software development.

They're also one of the most common avoidable engineering failures.

A reliable, comfortable build system has measurable benefits for software +development. Being able to build a testable, deployable system at any point +during development lets the team test more frequently. Frequent testing +isolates bugs and integration problems earlier, reducing their impact. Simple, +working builds allow new team members to ramp up more quickly on a project: +once they understand how one piece of the system is constructed, they can +apply that knowledge to the entire system and move on to doing useful work. If +releases, the points where code is made available outside the development +team, are done using the same build system that developers use in daily life, +there will be fewer surprises during releases as the “release” build process +will be well-understood from development.

Builds Have Needs, Too

In 1947, Abraham Maslow described a hierarchy of +needs for a +person's physical and mental well-being on the premise that all the items at +the lowest level of the hierarchy must be met before a person will be able to +focus usefully on higher-level needs. Maslow's hierarchy begins with a set of +needs that, without which, you do not have a person (for long)—physiological +needs like “breathing,” “food,” and “water.” At the peak, there are extremely +high-level needs that are about being a happy and enlightened +person—“creativity,” “morality,” “curiosity,” and so on.

A three-tier pyramid. At the bottom: Automatable. Repeatable. Standardized.
+Extensible. Understood. In the middle tier: Simple. Fast. Unit tests. Part of
+the project. Environment independent. At the top: Metrics. Parallel builds.
+Acceptance tests. Product caching. IDE
+integration.

Builds, and software engineering as a whole, can be described the same way: at +the top of the hierarchy is a working system that solves a problem, and at the +bottom are the things you need to have software at all. If you don't meet +needs at a given level, you will eventually be forced to stop what you're +doing at a higher level and face them.

Before a build is a build, there are five key needs to meet:

It must be repeatable. Every time you start your build on a given source + tree, it must build exactly the same products without any further + intervention. Without this, you can't reliably decide whether a given build + is “good,” and can easily wind up with a build that needs to be run several + times, or a build that relies on running several commands in the right + order, to produce a build.
It must be automatable. Build systems are used by developers sitting at + their desks, but they’re also used by automatic build systems for nightly + builds and continuous integration, and they can be made into parts of other + builds. A build system that can only be run by having someone sit down at a + keyboard and mouse and kicking it off can’t be integrated into anything + else.
It must be standardized. If you have multiple projects that build + similar things—for example, several Java libraries—all of them must be built + the same way. Without this, it's difficult for a developer to apply + knowledge from one project to another, and it's difficult to debug problems + with individual builds.
It must be extensible. Not all builds are created equal. Where one build + compiles a set of source files, another needs five libraries and a WSDL + descriptor before it can compile anything. There must be affordances within + the standard build that allow developers to describe the ways their build is + different. Without this, you have to write what amounts to a second build + tool to ensure that all the “extra” steps for certain projects happen.
Someone must understand it. A build nobody understands is a time bomb: + when it finally breaks (and it will), your project will be crippled until + someone fixes it or, more likely, hacks around it.

If you have these five things, you have a working build. The next step is to +make it comfortable. Comfortable builds can be used daily for development +work, demonstrations, and tests as well as during releases; builds that are +used constantly don't get a chance to “rust” as developers ignore them until a +release or a demo and don’t hide surprises for launch day.

It must be simple. When a complicated build breaks, you need someone who + understands it to fix it for you. Simple builds mean more people can + understand it and fewer things can break.
It must be fast. A slow build will be hacked around or ignored entirely. + Ideally, someone creating a local build for a small change should have a + build ready in seconds.
It must be part of the product. The team responsible for developing a + project must be in control of and responsible for its build. Changes to it + and bugs against it must be treated as changes to the product or bugs in the + product.
It must run unit tests. Unit tests, which are completely isolated tests + written by and for developers, can catch a large number of bugs, but they're + only useful if they get run. The build must run the unit test suite for the + product it's building every build.
It must build the same thing in any environment. A build is no good if + developers can only get a working build from a specific machine, or where a + build from one developer's machine is useless anywhere else. If the build is + uniform on any environment, any developer can cook up a build for a test or + demo at any time.

Finally, there are “chrome” features that take a build from effective to +excellent. These vary widely from project to project and from organization to +organization. Here are some common chrome needs:

It should integrate with your IDEs. This goes both directions: it should + be possible to run the build without leaving your IDE or editor suite, and + it should be possible to translate the build system into IDE-specific + configurations to reduce duplication between IDE settings and the build + configuration.
It should generate metrics. If you gather metrics for test coverage, + common bugs, complexity analysis, or generate reports or documentation, the + build system should be responsible for it. This keeps all the common + administrative actions for the project in the same place as the rest of the + configuration, and provides the same consistency that the system gives the + rest of the build.
It should support multiple processors. For medium-sized builds that + aren’t yet large enough to merit breaking down into libraries, being able to + perform independent build steps in parallel can be a major time-saver. This + can extend to distributed build systems, where idle CPU time can be donated + to other peoples’ builds.
It should run integration and acceptance tests. Taking manual work from + the quality control phase of a project and running it automatically during + builds amplifies the benefits of early testing and, if your acceptance tests + are good, when your project is done.
It should not need repeating. Once you declare a particular set of build + products “done,” you should be able to use those products as-is any time you + need them. Without this, you will eventually find yourself rebuilding the + same code from the same release over and over again.

What Doesn’t Work

Builds, like any other part of software development, have +antipatterns—recurring techniques for solving a problem that introduce more +problems.

One Source Tree, Many Products. Many small software projects that + survive to grow into large, monolithic projects are eventually broken up + into components. It's easy to do this by taking the existing source tree and + building parts of it, and it's also wrong. Builds that slice up a single + source tree require too much discipline to maintain and too much mental + effort to understand. Break your build into separate projects that are built + separately, and have each build produce one product.
The Build And Deploy System. Applications that have a server component + often choose to automate deployment and setup using the same build system + that builds the project. Too often, the extra build steps that set up a + working system from the built project are tacked onto the end of an existing + build. This breaks standardization, making that build harder to understand, + and means that that one build is producing more than one thing—it's + producing the actual project, and a working system around the project.
The Build Button. IDEs are really good at editing code. Most of them + will produce a build for you, too. Don't rely on IDE builds for your build + system, and don't let the IDE reconfigure the build process. Most IDEs don't + differentiate between settings that apply to the project and settings that + apply to the local environment, leading to builds that rely on libraries or + other projects being in specific places and on specific IDE settings that + are often buried in complex settings dialogs.
Manual Steps. Anything that gets done by hand will eventually be done + wrong. Automate every step.

What Does Work

Similarly, there are patterns—solutions that recur naturally and can be +applied to many problems.

Do One Thing Well. The UNIX philosophy of small, cohesive tools works + for build systems, too: if you need to build a package, and then install it + on a server, write three builds: one that builds the package, one that takes + a package and installs it, and a third that runs the first two builds in + order. The individual builds will be small enough to easily understand and + easy to standardize, and the package ends up installed on the server when + the main build finishes.
Dependency Repositories. After a build is done, make the built product + available to other builds and to the user for reuse rather than rebuilding + it every time you need it. Similarly, libraries and other inward + dependencies for a build can be shared between builds, reducing duplication + between projects.
Convention Over Extension. While it's great that your build system is + extensible, think hard about whether you really need to extend your build. + Each extension makes that project’s build that much harder to understand and + adds one more point of failure.

Pick A Tool, Any Tool

Nothing here is new. The value of build systems has been +discussed +in +great +detail elsewhere. +Much of the accumulated build wisdom of the software industry has already been +incorporated to one degree or another into build tools. What matters is that +you pick one, then use it with the discipline needed to get repeatable results +without thinking.

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