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goawsroles provides an interface and sample implementations for safe handling of AWS credentials. While typically used with the godynamo package (, it is useful on its own and should be easy to integrate into any package requiring a consistent interface for AWS credentials.

Typically, AWS credentials consist of a AccessKey, Secret and optionally a Token if temporary credentials are used. We want to be able to safely update these and access them in programs. It is useful to have a variety of mechanisms for sourcing these credentials - hardcoded, environment variables, or local files. goawsroles seeks to provide one interface for these and other scenarios, with the goal being safe access to read and update credential data.

At SmugMug, our typical use involves local files in /etc for each of the AccessKey, Secret and Token. These are updated by another process every thirty minutes. Local files provide for ease-of-use with some decent security via user and group permissions that are more effective than environment-variable based solutions. The RolesFiles implementation included here provides a solution for this scenario; it includes a RolesWatch method which, when launched via a goroutine, will watch the local permissions files for updates. When all three files are updated within a sane time interval, the internal representation of the permission strings for the AccessKey, Secret and Token will be updated. Using this mechanism along with another process to keep our local files updated and valid, we can be sure that any time we call the Get method on the RolesFiles instance, we are getting fresh credentials.

RolesFiles Example

This example is contained within the unit test for the RolesFiles instance, with some extra comments.

    func TestRolesWatcher(t *testing.T) {

        // This roles instance reads from files
        rw := NewRolesFiles()

        // This is where our external process would place files containing
        // credential data retrieved from AWS.
        rw.BaseDir = "./test_files"

        // The files underneath the BaseDir for the respective credential parts.
        rw.AccessKeyFile = "role_access_key"
        rw.SecretFile = "role_secret_key"
        rw.TokenFile = "role_token"

        // We want to read the credential data once to make sure we can do
        // so correctly in the foreground.
        rw_err := rw.RolesRead()
        if rw_err != nil {
            t.Errorf("roles read err")

        // We are about to launch our file watcher in the background. Once launched,
        // the var `rw` will be considered to always have the newest credential information.

        // `c` is a channel for the RolesWatcher to send errors on
        c := make(chan error)
        // `s` is a channel for the RolesWatcher to tell us when it has refreshed credentials.
        s := make(chan bool)

        go rw.RolesWatch(c, s)

        go func() {
            for {
                select {
                    // This case tells us the files have been re-read
                    case <-s:
                        fmt.Printf("\n*********** re-read the files\n")
                        accessKey, secret, token, get_err := rw.Get()
                        if get_err != nil {
                            e := fmt.Sprintf("cannot get a role file:%s\n", get_err.Error()
                        } else {
                            fmt.Printf("new data\naccess key:%s\nsecret:%s\ntoken:%s\n",
                                       accessKey, secret, token)
                    // We want to short-circuit the test after five seconds
                    case <-time.After(5 * time.Second):
                        fmt.Printf("exiting watcher loop\n")
                        c <- nil

        // Give the RolesWatcher a second to start watching files.
        time.Sleep(1 * time.Second)
        // Now we want to touch our files to change their timestamp, which should
        // trigger the RolesWatcher to re-read them, which will then cause a message
        // to be sent on the `s` channel above.
        touch_cmd1 := exec.Command("touch",rw.BaseDir + string(filepath.Separator) + rw.AccessKeyFile)
        touch_cmd2 := exec.Command("touch",rw.BaseDir + string(filepath.Separator) + rw.SecretFile)
        touch_cmd3 := exec.Command("touch",rw.BaseDir + string(filepath.Separator) + rw.TokenFile)
        touch_err1 := touch_cmd1.Run()
        if touch_err1 != nil {
        touch_err2 := touch_cmd2.Run()
        if touch_err2 != nil {
        touch_err3 := touch_cmd3.Run()
        if touch_err3 != nil {
        time.Sleep(2 * time.Second)

        // If this is triggered, then it means something went wrong reading the credentials files.
        watch_err := <-c
        if watch_err != nil {
            e := fmt.Sprintf("error from watcher: %s\n", watch_err.Error())


This instance of the RolesReader interface only accepts a one-time initialization of the AccessKey and Secret. Since "master" credentials do not contain a Token, it is forced to be empty. This instance will panic if RolesWatch is called, as this instance does not support the concept of online updating. Using this package is trivial: instantiate a new instance with NewRolesMasterCredentials(accessKey, secret) and extract the values with the various Get* functions.


This is the simplest RolesReader interface. It is just a safe container for the AccessKey, Secret and Token. Unlike RolesMaster, a token can be set. This instance will panic if RolesWatch is called, as this instance does not support the concept of online updating. Using this package is trivial: instantiate a new instance with NewRolesSimple(accessKey, secret, token) and extract the values with the various Get* functions.


    go get
    go get
    go get

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