Buildpack: Go

This is a buildpack for Go.

Getting Started

Follow the guide at https://doc.scalingo.com/languages/go/start.

There's also a hello world sample app at https://github.com/Scalingo/sample-go-martini.

Example

$ ls -A1
.git
vendor
Procfile
web.go

$ scalingo create my-go-app
$ git push scalingo master
-----> Go app detected
-----> Installing go1.11... done
-----> Running: go install -tags paas .
-----> Discovering process types
       Procfile declares types -> web
        Build complete, shipping your container...
         Waiting for your application to boot...
          <-- https://my-go-app.osc-fr1.scalingo.io -->

This buildpack will detect your repository as Go if you are using either:

• go modules
• dep
• govendor
• glide
• GB
• Godep

This buildpack adds a paas build constraint, to enable Scalingo-specific code. See the App Engine build constraints article for more.

Go Module Specifics

When using go modules, this buildpack will search the code base for main packages, ignoring any in vendor/, and will automatically compile those packages. If this isn't what you want you can specify specific package spec(s) via the go.mod file's // +scalingo install directive (see below).

The go.mod file allows for arbitrary comments. This buildpack utilizes build constraint style comments to track Scalingo build specific configuration which is encoded in the following way:

• // +scalingo goVersion <version>: the major version of go you would like Scalingo to use when compiling your code. If not specified this defaults to the buildpack's DefaultVersion. Specifying a version < go1.11 will cause a build error because modules are not supported by older versions of go.

  Example: // +scalingo goVersion go1.11

• // +scalingo install <packagespec>[, <packagespec>]: a space separated list of the packages you want to install. If not specified, the buildpack defaults to detecting the main packages in the code base. Generally speaking this should be sufficient for most users. If this isn't what you want you can instruct the buildpack to only build certain packages via this option. Other common choices are: ./cmd/... (all packages and sub packages in the cmd directory) and ./... (all packages and sub packages of the current directory). The exact choice depends on the layout of your repository though.

  Example: // +scalingo install ./cmd/... ./special

If a top level vendor directory exists and the go.sum file has a size greater than zero, go install is invoked with -mod=vendor, causing the build to skip downloading and checking of dependencies. This results in only the dependencies from the top level vendor directory being used.

Pre/Post Compile Hooks

If the file bin/go-pre-compile or bin/go-post-compile exists and is executable then it will be executed either before compilation (go-pre-compile) of the repo, or after compilation (go-post-compile).

These hooks can be used to install additional tools, such as github.com/golang-migrate/migrate:

#!/bin/bash
set -e

go install -tags 'postgres' github.com/golang-migrate/migrate/v4/cmd/[email protected]

Because the buildpack installs compiled executables to bin, the go-post-compile hook can be written in go if it's installed by the specified <packagespec> (see above).

Example:

$ cat go.mod
// +scalingo install ./cmd/...
$ ls -F cmd
client/ go-post-compile/ server/

dep specifics

The Gopkg.toml file allows for arbitrary, tool specific fields. This buildpack utilizes this feature to track build specific configuration which are encoded in the following way:

• metadata.scalingo['root-package'] (String): the root package name of the packages you are pushing to Scalingo.You can find this locally with go list -e .. There is no default for this and it must be specified.

• metadata.scalingo['go-version'] (String): the major version of go you would like Scalingo to use when compiling your code. If not specified this defaults to the buildpack's DefaultVersion. Exact versions (ex go1.9.4) can also be specified if needed, but is not generally recommended. Since Go doesn't release .0 versions, specifying a .0 version will pin your code to the initial release of the given major version (ex go1.10.0 == go1.10 w/o auto updating to go1.10.1 when it becomes available).

• metadata.scalingo['install'] (Array of Strings): a list of the packages you want to install. If not specified, this defaults to ["."]. Other common choices are: ["./cmd/..."] (all packages and sub packages in the cmd directory) and ["./..."] (all packages and sub packages of the current directory). The exact choice depends on the layout of your repository though. Please note that ./..., for versions of go < 1.9, includes any packages in your vendor directory.

• metadata.scalingo['ensure'] (String): if this is set to false then dep ensure is not run.

• metadata.scalingo['additional-tools'] (Array of Strings): a list of additional tools that the buildpack is aware of that you want it to install. If the tool has multiple versions an optional @<version> suffix can be specified to select that specific version of the tool. Otherwise the buildpack's default version is chosen. Currently the only supported tool is github.com/golang-migrate/migrate at v3.4.0 (also the default version).

[metadata.scalingo]
  root-package = "github.com/Scalingo/fixture"
  go-version = "go1.8.3"
  install = [ "./cmd/...", "./foo" ]
  ensure = "false"
  additional-tools = ["github.com/golang-migrate/migrate"]
...

govendor specifics

The vendor.json spec that govendor follows for its metadata file allows for arbitrary, tool specific fields. This buildpack uses this feature to track build specific bits. These bits are encoded in the following top level json keys:

• rootPath (String): the root package name of the packages you are pushing to Scalingo. You can find this locally with go list -e .. There is no default for this and it must be specified. Recent versions of govendor automatically fill in this field for you. You can re-run govendor init after upgrading to have this field filled in automatically, or it will be filled the next time you use govendor to modify a dependency.

• scalingo.goVersion (String): the major version of go you would like Scalingo to use when compiling your code. If not specified this defaults to the buildpack's DefaultVersion. Exact versions (ex go1.9.4) can also be specified if needed, but is not generally recommended. Since Go doesn't release .0 versions, specifying a .0 version will pin your code to the initial release of the given major version (ex go1.10.0 == go1.10 w/o auto updating to go1.10.1 when it becomes available).

• scalingo.install (Array of Strings): a list of the packages you want to install. If not specified, this defaults to ["."]. Other common choices are: ["./cmd/..."] (all packages and sub packages in the cmd directory) and ["./..."] (all packages and sub packages of the current directory). The exact choice depends on the layout of your repository though. Please note that ./... includes any packages in your vendor directory.

• scalingo.additionalTools (Array of Strings): a list of additional tools that the buildpack is aware of that you want it to install. If the tool has multiple versions an optional @<version> suffix can be specified to select that specific version of the tool. Otherwise the buildpack's default version is chosen. Currently the only supported tool is github.com/golang-migrate/migrate at v3.4.0 (also the default version).

Example with everything, for a project using go1.9, located at $GOPATH/src/github.com/Scalingo/sample-go-martini and requiring a single package spec of ./... to install.

{
    ...
    "rootPath": "github.com/Scalingo/sample-go-martini",
    "scalingo": {
        "install" : [ "./..." ],
        "goVersion": "go1.9"
         },
    ...
}

A tool like jq or a text editor can be used to inject these variables into vendor/vendor.json.

glide specifics

The glide.yaml and glide.lock files do not allow for arbitrary metadata, so the buildpack relies solely on the glide command and environment variables to control the build process.

The base package name is determined by running glide name.

The Go version used to compile code defaults to the buildpack's DefaultVersion. This can be overridden by the $GOVERSION environment variable. Setting $GOVERSION to a major version will result in the buildpack using the latest released minor version in that series. Setting $GOVERSION to a specific minor Go version will pin Go to that version. Since Go doesn't release .0 versions, specifying a .0 version will pin your code to the initial release of the given major version (ex go1.10.0 == go1.10 w/o auto updating to go1.10.1 when it becomes available).

Examples:

$ scalingo env-set GOVERSION=go1.9   # Will use go1.9.X, Where X is that latest minor release in the 1.9 series
$ scalingo env-set GOVERSION=go1.7.5 # Pins to go1.7.5

glide install will be run to ensure that all dependencies are properly installed. If you need the buildpack to skip the glide install you can set $GLIDE_SKIP_INSTALL to true. Example:

$ scalingo env-set GLIDE_SKIP_INSTALL=true
$ git push scalingo master

Installation defaults to .. This can be overridden by setting the $GO_INSTALL_PACKAGE_SPEC environment variable to the package spec you want the go tool chain to install. Example:

$ scalingo env-set GO_INSTALL_PACKAGE_SPEC=./...
$ git push scalingo master

Usage with other vendoring systems

If your vendor system of choice is not listed here or your project only uses packages in the standard library, create vendor/vendor.json with the following contents, adjusted as needed for your project's root path.

{
    "comment": "For other Scalingo options see: http://doc.scalingo.com/languages/go",
    "rootPath": "github.com/yourOrg/yourRepo",
    "scalingo": {
        "sync": false
    }
}

Default Procfile

If there is no Procfile in the base directory of the code being built and the buildpack can figure out the name of the base package (also known as the module), then a default Procfile is created that includes a web process type that runs the resulting executable from compiling the base package.

For example, if the package name was github.com/Scalingo/example, this buildpack would create a Procfile that looks like this:

$ cat Procfile
web: example

This is useful when the base package is also the only main package to build.

If you have adopted the cmd/<executable name> structure this won't work and you will need to create a Procfile.

Note: This buildpack should be able to figure out the name of the base package in all cases, except when gb is being used.

Private Git Repos

The buildpack installs a custom git credential handler. Any tool that shells out to git (most do) should be able to transparently use this feature. Note: It has only been tested with Github repos over https using personal access tokens.

The custom git credential handler searches the application's config vars for vars that follow the following pattern: GO_GIT_CRED__<PROTOCOL>__<HOSTNAME>. Any periods (.) in the HOSTNAME must be replaces with double underscores (__).

The value of a matching var will be used as the username. If the value contains a ":", the value will be split on the ":" and the left side will be used as the username and the right side used as the password. When no password is present, x-oauth-basic is used.

The following example will cause git to use the FakePersonalAccessTokenHere as the username when authenticating to github.com via https:

$ scalingo env-set GO_GIT_CRED__HTTPS__GITHUB__COM=FakePersoalAccessTokenHere

Hacking on this Buildpack

To change this buildpack, fork it on GitHub & push changes to your fork. Ensure that tests have been added to test/run.sh and any corresponding fixtures to test/fixtures/<fixture name>.

Tests

Make, jq & docker are required to run tests.

make test

Run a specific test in test/run.sh:

make BASH_COMMAND='test/run.sh -- testGBVendor' test

Compiling a fixture locally

Make & docker are required to compile a fixture.

make FIXTURE=<fixture name> compile

You will then be dropped into a bash prompt in the container that the fixture was compiled in.

Using with cgo

The buildpack supports building with C dependencies via cgo. You can set config vars to specify CGO flags to specify paths for vendored dependencies. The literal text of ${build_dir} will be replaced with the directory the build is happening in. For example, if you added C headers to an includes/ directory, add the following config to your app: scalingo env-set CGO_CFLAGS='-I${ build_dir}/includes'. Note the used of '' to ensure they are not converted to local environment variables

Using a development version of Go

The buildpack can install and use any specific commit of the Go compiler when the specified go version is devel-<short sha>. The version can be set either via the appropriate vendoring tools config file or via the $GOVERSION environment variable. The specific sha is downloaded from Github w/o git history. Builds may fail if GitHub is down, but the compiled go version is cached.

When this is used the buildpack also downloads and installs the buildpack's current default Go version for use in bootstrapping the compiler.

Build tests are NOT RUN. Go compilation failures will fail a build.

No official support is provided for unreleased versions of Go.

Passing a symbol (and optional string) to the linker

This buildpack supports the go linker's ability (-X symbol value) to set the value of a string at link time. This can be done by setting GO_LINKER_SYMBOL and GO_LINKER_VALUE in the application's config before pushing code. If GO_LINKER_SYMBOL is set, but GO_LINKER_VALUE isn't set then GO_LINKER_VALUE defaults to $SOURCE_VERSION.

This can be used to embed the commit sha, or other build specific data directly into the compiled executable.

If the source code contains a golanglint-ci configuration file in the root of the source code (one of /.golangci.yml, /.golangci.toml, or /.golangci.json) then golanci-lint is run at the start of the test phase.

Use one of those configuration files to configure the golanglint-ci run.