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Replace dumb-init with go init (redhat-developer#35)
* Moving to use go-init instead of dumb-init Signed-off-by: Mohammed Zeeshan Ahmed <mohammed.zee1000@gmail.com> * Moving go-init out of vendor and updating Dockerfile accordingly * Commenting out everything that has to do with dumb-init from Dockerfile * Removing dumb-init and any remaining references * Updating image to follow /go/src/github.com/pablo-ruth/go-init
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,68 @@ | ||
| # go-init | ||
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| [](https://travis-ci.org/pablo-ruth/go-init) | ||
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| **go-init** is a minimal init system with simple *lifecycle management* heavily inspired by [dumb-init](https://github.com/Yelp/dumb-init). | ||
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| It is designed to run as the first process (PID 1) inside a container. | ||
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| It is lightweight (less than 500KB after UPX compression) and statically linked so you don't need to install any dependency. | ||
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| ## Download | ||
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| You can download the latest version on [releases page](https://github.com/pablo-ruth/go-init/releases) | ||
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| ## Why you need an init system | ||
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| I can't explain it better than Yelp in *dumb-init* repo, so please [read their explanation](https://github.com/Yelp/dumb-init/blob/v1.2.0/README.md#why-you-need-an-init-system) | ||
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| Summary: | ||
| - Proper signal forwarding | ||
| - Orphaned zombies reaping | ||
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| ## Why another minimal init system | ||
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| In addition to *init* problematic, **go-init** tries to solve another Docker flaw by adding *hooks* on start and stop of the main process. | ||
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| If you want to launch a command before the main process of your container and another one after the main process exit, you can't with Docker, see [issue 6982](https://github.com/moby/moby/issues/6982) | ||
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| With **go-init** you can do that with "pre" and "post" hooks. | ||
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| ## Usage | ||
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| ### one command | ||
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| ``` | ||
| $ go-init -main "my_command param1 param2" | ||
| ``` | ||
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| ### pre-start and post-stop hooks | ||
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| ``` | ||
| $ go-init -pre "my_pre_command param1" -main "my_command param1 param2" -post "my_post_command param1" | ||
| ``` | ||
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| ## docker | ||
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| Example of Dockerfile using *go-init*: | ||
| ``` | ||
| FROM alpine:latest | ||
| COPY go-init /bin/go-init | ||
| RUN chmod +x /bin/go-init | ||
| ENTRYPOINT ["go-init"] | ||
| CMD ["-pre", "echo hello world", "-main", "sleep 5", "-post", "echo I finished my sleep bye"] | ||
| ``` | ||
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| Build it: | ||
| ``` | ||
| docker build -t go-init-example | ||
| ``` | ||
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| Run it: | ||
| ``` | ||
| docker run go-init-example | ||
| ``` |
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| Original file line number | Diff line number | Diff line change |
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| package main | ||
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| import ( | ||
| "context" | ||
| "flag" | ||
| "fmt" | ||
| "log" | ||
| "os" | ||
| "os/exec" | ||
| "os/signal" | ||
| "strings" | ||
| "sync" | ||
| "syscall" | ||
| "time" | ||
| ) | ||
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| var ( | ||
| versionString = "undefined" | ||
| ) | ||
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| func main() { | ||
| var preStartCmd string | ||
| var mainCmd string | ||
| var postStopCmd string | ||
| var version bool | ||
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| flag.StringVar(&preStartCmd, "pre", "", "Pre-start command") | ||
| flag.StringVar(&mainCmd, "main", "", "Main command") | ||
| flag.StringVar(&postStopCmd, "post", "", "Post-stop command") | ||
| flag.BoolVar(&version, "version", false, "Display go-init version") | ||
| flag.Parse() | ||
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| if version { | ||
| fmt.Println(versionString) | ||
| os.Exit(0) | ||
| } | ||
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| if mainCmd == "" { | ||
| log.Fatal("[go-init] No main command defined, exiting") | ||
| } | ||
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| // Routine to reap zombies (it's the job of init) | ||
| ctx, cancel := context.WithCancel(context.Background()) | ||
| var wg sync.WaitGroup | ||
| wg.Add(1) | ||
| go removeZombies(ctx, &wg) | ||
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| // Launch pre-start command | ||
| if preStartCmd == "" { | ||
| log.Println("[go-init] No pre-start command defined, skip") | ||
| } else { | ||
| log.Printf("[go-init] Pre-start command launched : %s\n", preStartCmd) | ||
| err := run(preStartCmd) | ||
| if err != nil { | ||
| log.Println("[go-init] Pre-start command failed") | ||
| log.Printf("[go-init] %s\n", err) | ||
| cleanQuit(cancel, &wg, 1) | ||
| } else { | ||
| log.Printf("[go-init] Pre-start command exited") | ||
| } | ||
| } | ||
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| // Launch main command | ||
| var mainRC int | ||
| log.Printf("[go-init] Main command launched : %s\n", mainCmd) | ||
| err := run(mainCmd) | ||
| if err != nil { | ||
| log.Println("[go-init] Main command failed") | ||
| log.Printf("[go-init] %s\n", err) | ||
| mainRC = 1 | ||
| } else { | ||
| log.Printf("[go-init] Main command exited") | ||
| } | ||
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| // Launch post-stop command | ||
| if postStopCmd == "" { | ||
| log.Println("[go-init] No post-stop command defined, skip") | ||
| } else { | ||
| log.Printf("[go-init] Post-stop command launched : %s\n", postStopCmd) | ||
| err := run(postStopCmd) | ||
| if err != nil { | ||
| log.Println("[go-init] Post-stop command failed") | ||
| log.Printf("[go-init] %s\n", err) | ||
| cleanQuit(cancel, &wg, 1) | ||
| } else { | ||
| log.Printf("[go-init] Post-stop command exited") | ||
| } | ||
| } | ||
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| // Wait removeZombies goroutine | ||
| cleanQuit(cancel, &wg, mainRC) | ||
| } | ||
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| func removeZombies(ctx context.Context, wg *sync.WaitGroup) { | ||
| for { | ||
| var status syscall.WaitStatus | ||
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| // Wait for orphaned zombie process | ||
| pid, _ := syscall.Wait4(-1, &status, syscall.WNOHANG, nil) | ||
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| if pid <= 0 { | ||
| // PID is 0 or -1 if no child waiting | ||
| // so we wait for 1 second for next check | ||
| time.Sleep(1 * time.Second) | ||
| } else { | ||
| // PID is > 0 if a child was reaped | ||
| // we immediately check if another one | ||
| // is waiting | ||
| continue | ||
| } | ||
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| // Non-blocking test | ||
| // if context is done | ||
| select { | ||
| case <-ctx.Done(): | ||
| // Context is done | ||
| // so we stop goroutine | ||
| wg.Done() | ||
| return | ||
| default: | ||
| } | ||
| } | ||
| } | ||
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| func run(command string) error { | ||
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| var commandStr string | ||
| var argsSlice []string | ||
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| // Split cmd and args | ||
| commandSlice := strings.Fields(command) | ||
| commandStr = commandSlice[0] | ||
| // if there is args | ||
| if len(commandSlice) > 1 { | ||
| argsSlice = commandSlice[1:] | ||
| } | ||
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| // Register chan to receive system signals | ||
| sigs := make(chan os.Signal, 1) | ||
| defer close(sigs) | ||
| signal.Notify(sigs) | ||
| defer signal.Reset() | ||
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| // Define command and rebind | ||
| // stdout and stdin | ||
| cmd := exec.Command(commandStr, argsSlice...) | ||
| cmd.Stdout = os.Stdout | ||
| cmd.Stderr = os.Stderr | ||
| // Create a dedicated pidgroup | ||
| // used to forward signals to | ||
| // main process and all children | ||
| cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true} | ||
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| // Goroutine for signals forwarding | ||
| go func() { | ||
| for sig := range sigs { | ||
| // Ignore SIGCHLD signals since | ||
| // thez are only usefull for go-init | ||
| if sig != syscall.SIGCHLD { | ||
| // Forward signal to main process and all children | ||
| syscall.Kill(-cmd.Process.Pid, sig.(syscall.Signal)) | ||
| } | ||
| } | ||
| }() | ||
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| // Start defined command | ||
| err := cmd.Start() | ||
| if err != nil { | ||
| return err | ||
| } | ||
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| // Wait for command to exit | ||
| err = cmd.Wait() | ||
| if err != nil { | ||
| return err | ||
| } | ||
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| return nil | ||
| } | ||
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| func cleanQuit(cancel context.CancelFunc, wg *sync.WaitGroup, code int) { | ||
| // Signal zombie goroutine to stop | ||
| // and wait for it to release waitgroup | ||
| cancel() | ||
| wg.Wait() | ||
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| os.Exit(code) | ||
| } |
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