xk6 - Custom k6 Builder

This command line tool and associated Go package makes it easy to make custom builds of k6.

It is used heavily by k6 extension developers as well as anyone who wishes to make custom k6 binaries (with or without extensions).

Docker

The easiest way to use xk6 is via our Docker image. This avoids having to setup a local Go environment, and install xk6 manually.

For example, to build a k6 v0.45.1 binary on Linux with the xk6-kafka and xk6-output-influxdb extensions, you would run:

docker run --rm -it -u "$(id -u):$(id -g)" -v "${PWD}:/xk6" grafana/xk6 build v0.45.1 \
  --with github.com/mostafa/xk6-kafka@v0.17.0 \
  --with github.com/grafana/xk6-output-influxdb@v0.3.0

This would create a k6 binary in the current working directory.

Note the use of the -u (user) option to specify the user and group IDs of the account on the host machine. This is important for the k6 file to have the same file permissions as the host user.

The -v (volume) option is also required to mount the current working directory inside the container, so that the k6 binary can be written to it.

Note that if you're using SELinux, you might need to add :z to the --volume option to avoid permission errors. E.g. -v "${PWD}:/xk6:z".

If you prefer to setup Go and use xk6 without Docker, see the "Local Installation" section below.

macOS

On macOS you will need to set the GOOS=darwin environment variable to build a macOS binary.

You can do this with the --env or -e argument to docker run:

docker run --rm -it -e GOOS=darwin -u "$(id -u):$(id -g)" -v "${PWD}:/xk6" \
  grafana/xk6 build v0.45.1 \
  --with github.com/mostafa/xk6-kafka@v0.17.0 \
  --with github.com/grafana/xk6-output-influxdb@v0.3.0

Windows

On Windows you can either build a native Windows binary, or, if you're using WSL2, a Linux binary you can use in WSL2.

For the native Windows binary if you're using PowerShell:

docker run --rm -it -e GOOS=windows -u "$(id -u):$(id -g)" -v "${PWD}:/xk6" `
  grafana/xk6 build v0.45.1 --output k6.exe `
  --with github.com/mostafa/xk6-kafka@v0.17.0 `
  --with github.com/grafana/xk6-output-influxdb@v0.3.0

For the native Windows binary if you're using cmd.exe:

docker run --rm -it -e GOOS=windows -v "%cd%:/xk6" ^
  grafana/xk6 build v0.45.1 --output k6.exe ^
  --with github.com/mostafa/xk6-kafka@v0.17.0 ^
  --with github.com/grafana/xk6-output-influxdb@v0.3.0

For the Linux binary on WSL2, you can use the same command as for Linux.

Local Installation

Requirements

• Go installed. At least version 1.17 is needed.

Install xk6

go install go.k6.io/xk6/cmd/xk6@latest

This will install the xk6 binary in your $GOPATH/bin directory.

If you're getting a command not found error when trying to run xk6, make sure that you precisely follow the Go installation instructions for your platform. Specifically, ensure that the $GOPATH/bin directory is part of your $PATH. For example, you might want to add this to your shell's initialization file: export PATH=$(go env GOPATH)/bin:$PATH. See this article for more information.

Command usage

The xk6 command has two primary uses:

1. Compile custom k6 binaries
2. A replacement for go run while developing k6 extensions

The xk6 command will use the latest version of k6 by default. You can customize this for all invocations by setting the K6_VERSION environment variable.

As usual with go command, the xk6 command will pass the GOOS, GOARCH, and GOARM environment variables through for cross-compilation.

Custom builds

Syntax:

xk6 build [<k6_version>]
    [--output <file>]
    [--with <module[@version][=replacement]>...]
    [--replace <module=replacement>...]

• <k6_version> is the core k6 version to build; defaults to K6_VERSION env variable or whatever is the latest version needed by all extensions. For example, if extension A requires k6 v0.41.0 and extension B requires k6 v0.43.0, the final k6 version used in the binary will be v0.43.0. Note that depending on the differences in these versions, this behavior might cause the build to fail. This is something enforced by the Go build system, and we have no way of fixing it.
• --output changes the output file.
• --with can be used multiple times to add extensions by specifying the Go module name and optionally its version, similar to go get. Module name is required, but specific version and/or local replacement are optional. For an up-to-date list of k6 extensions, head to our extensions page.
• --replace can be used multiple times to add replacements by specifying the Go module name and the replacement module, similar to go mod edit -replace=. Version of the replacement can be specified with the @version suffix in the replacement path.

Examples:

xk6 build \
    --with github.com/grafana/xk6-browser

xk6 build v0.35.0 \
    --with github.com/grafana/xk6-browser@v0.1.1

xk6 build \
    --with github.com/grafana/xk6-browser=../../my-fork

xk6 build \
    --with github.com/grafana/xk6-browser=.

xk6 build \
    --with github.com/grafana/xk6-browser@v0.1.1=../../my-fork

# Build using a k6 fork repository. Note that a version is required if
# XK6_K6_REPO is a URI.
XK6_K6_REPO=github.com/example/k6 xk6 build master \
    --with github.com/grafana/xk6-browser

# Build using a k6 fork repository from a local path. The version must be omitted
# and the path must be absolute.
XK6_K6_REPO="$PWD/../../k6" xk6 build \
    --with github.com/grafana/xk6-browser

For extension development

If you run xk6 from within the folder of the k6 extension you're working on without the build subcommand, it will build k6 with your current module and run it, as if you manually plugged it in and invoked go run.

The binary will be built and run from the current directory, then cleaned up.

The current working directory must be inside an initialized Go module.

Also note that because of the way xk6 works, vendored dependencies (the vendor directory created by go mod vendor) will not be taken into account when building a binary, and you don't need to commit them to the extension repository.

Syntax:

xk6 <args...>

• <args...> are passed through to the k6 command.

For example:

xk6 version
xk6 run -u 10 -d 10s test.js

The race detector can be enabled by setting the env variable XK6_RACE_DETECTOR=1 or through the XK6_BUILD_FLAGS env variable.

Library usage

builder := xk6.Builder{
    K6Version: "v0.35.0",
    Extensions: []xk6.Dependency{
        {
            PackagePath: "github.com/grafana/xk6-browser",
            Version:     "v0.1.1",
        },
    },
}
err := builder.Build(context.Background(), "./k6")

Versions can be anything compatible with go get.

Environment variables

Because the subcommands and flags are constrained to benefit rapid extension prototyping, xk6 does read some environment variables to take cues for its behavior and/or configuration when there is no room for flags.

• K6_VERSION sets the version of k6 to build.
• XK6_BUILD_FLAGS sets any go build flags if needed. Defaults to '-ldflags=-w -s'.
• XK6_RACE_DETECTOR=1 enables the Go race detector in the build.
• XK6_SKIP_CLEANUP=1 causes xk6 to leave build artifacts on disk after exiting.
• XK6_K6_REPO optionally sets the path to the main k6 repository. This is useful when building with k6 forks.

Keeping dependencies in sync

We recommend extension maintainers to keep dependencies in common with k6 core in the same version k6 core uses. This guarantees binary compatibility of the JS runtime, and ensures uses will not have to face unforeseen build-time errors when compiling several extensions together with xk6.

The go-depsync tool can check for this automatically and produce a go get command that syncs common dependencies:

/your/extension$ go-depsync --parent go.k6.io/k6

This project originally forked from the xcaddy project. Thank you!