matttproud-soundcloud / visor

Client to bazooka's application registry

Visor

Visor is a library which provides an abstraction over a global process state.

Visor uses doozerd.

Usage

To understand how Visor works, we need to understand how it works with time. Each of the Visor data-types App, Revision, Proctype and Instance are snapshots of a specific point in time in the coordinator. When a mutating operation is successfully performed on one of these data-types, a new snapshot is returned, representing the state of the coordinator after the operation. If the operation would fail, the old snapshot is returned with an error.

With the new snapshot, we can perform an operation on this new state, and so on with every new snapshot.

package main

import "github.com/soundcloud/visor"
import "log"

func main() {
    snapshot, err := visor.DialUri("doozer:?ca=localhost:8046", "/")

    name  := "rocket"
    stack := "HEAD" // Runtime stack revision
    repo  := "http://github.com/bazooka/rocket"

    app   := visor.NewApp(name, repo, stack, snapshot)

    _, err := app.Register()
    if err != nil {
        log.Fatalf("error registering app: %s", err)
    }

    rev := visor.NewRevision(app, "f84e19", snapshot)
    rev.ArchiveUrl = "http://artifacts/rocket/f84e19.img"

    _, err = rev.Register()
    if err != nil {
        log.Fatalf("error registering revision: %s", err)
    }
}

Working with snapshots

// Get a snapshot of the latest coordinator state
snapshot, err := visor.DialUri("doozer:?ca=localhost:8046", "/")

// Get the list of applications at snapshot
apps, _ := visor.Apps(snapshot)
app := apps[0] // app.Rev == snapshot.Rev == 1

// Set some environment vars on *app*. Every time state is
// changed in the coordinator, a new App snapshot is returned.
app, _ = app.SetEnvironmentVar("cow", "moo")  // app.Rev == 2
app, _ = app.SetEnvironmentVar("cat", "meow") // app.Rev == 3

// Attempt to get a recently set environment var from an old snapshot (apps[0].Rev == 1)
apps[0].GetEnvironmentVar("cat") // "", ErrKeyNotFound

// Get a recently set environment var from the latest snapshot (app.Rev == 3)
app.GetEnvironmentVar("cat")     // "meow", nil

Watching for events

package main

import "soundcloud/visor"

func main() {
  snapshot, err := visor.DialUri("doozer:?ca=localhost:8046", "/")
  if err != nil {
    panic(err)
  }

  c := make(chan *visor.Event)

  go visor.WatchEvent(snapshot, c)

  // Read one event from the channel
  fmt.Println(<-c)
}

Development

Setup

Dependencies

• Go (go1)

• doozer (implicit)

  go get github.com/soundcloud/doozer
  

  if you run in trouble with the protobuf, do a:

  cd src/pkg/code.google.com/p/goprotobuf
  hg pull
  hg update 
  make install
  

• doozerd (testing)

  go get github.com/ha/doozerd
  

  if this fails, do the following

  cd $GOROOT/src/pkg/github.com/soundcloud/doozerd
  git remote add soundcloud [email protected]:soundcloud/doozerd
  git pull soundcloud master
  ./make.sh
  go install
  

Testing

First start doozerd with default configuration. Then run:

go test

Conventions

This repository follows the code conventions dictated by gofmt. To automate the formatting process install this pre-commit hook, which runs gofmt and adds the files. Don't forget to make the file executable: chmod +x .git/hooks/pre-commit.

Branching

See Guide.

Versioning

This project is versioned with the help of the Semantic Versioning Specification using 0.0.0 as the initial version. Please make sure you have read the guidelines before increasing a version number either for a release or a hotfix.