goswarm

goswarm is a tool that creates many gomotes and executes the same command on all of them, in a loop, until any one of them fails.

Installation

Install Go.

Then, install gomote:

go install golang.org/x/build/cmd/gomote@latest

Make sure that gomote is now in your path.

Finally, install this tool:

go install github.com/mknyszek/goswarm@latest

Usage

WARNING: This tool can spin up an arbitrary number of gomote instances so please take great care to ensure the gomote instance type you're spinning up does not have limited capacity, or that you're cleared to do this by the Go release team.

TODO: Make goswarm check for and reject limited-capacity instance types unless the user specifically acknowledges the risks.

The typical use-case is trying to reproduce a rarely-occuring bug, usually with the goal of capturing a core dump or attaching GDB to the process. This tool only focuses on the first half of the equation.

To execute all.bash on 10 (the default) NetBSD 9.0 gomotes at once, do

GOROOT=path/to/go/repo goswarm netbsd-386-9_0 go/src/all.bash

It's highly recommended to also pass a -match argument that executes until a failure whose output matches the provided regular expression is encountered. Even just -match="fatal error:" is quite effective. Without it, goswarm will stop even if gomote fails due to some unrelated error.

If -match is specified, unmatched failures will always be written to a temporary file in the default temporary directory for your platform. By default they will also be logged, but this can be disabled by setting -v to a value less than 2.

Core dumps

To capture core dump, add the following file to your Go repository (it does not need to be in git) as debug.bash (with the appropriate file permissions).

#!/usr/bin/env bash

set -e

ulimit -c unlimited

# Linux
# echo "/workdir/go/core.%e.%p" | sudo tee /proc/sys/kernel/core_pattern

# NetBSD
sysctl -w proc.$$.corename=$(dirname $0)/%n.%p.core

export GOTRACEBACK=crash
$(dirname $0)/all.bash

and invoke goswarm like so:

GOROOT=path/to/go/repo goswarm netbsd-386-9_0 go/src/debug.bash

goswarm will automatically copy down the full working directory on the gomote back as a gzipped tar (as per gomote gettar).

Clean up

goswarm purposefully does not clean up instances, so that the failing instance may be examined in more detail. The core dump likely must be manually extracted at this point by finding its location in the filesystem (depends on which process crashed) and using the gomote command to copy it back.

To clean up instances you created of a particular type, use the -clean flag.

goswarm -clean netbsd-386-9_0