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pkg: Add a generic metadata package
This package handles meta and user data for different cloud and other platforms. It should be easy to extend to new platforms. Currently, it handles GCP metadata and a simple CDROM userdata provider. Signed-off-by: Rolf Neugebauer <rolf.neugebauer@docker.com>
This commit is contained in:
Rolf Neugebauer
181
pkg/metadata/main.go
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181
pkg/metadata/main.go
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package main
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import (
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"encoding/json"
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"io/ioutil"
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"log"
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"os"
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"path"
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"strconv"
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"syscall"
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)
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const (
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// ConfigPath is where the data is extracted to
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ConfigPath = "/var/config"
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// MountPoint is where the CDROM is mounted
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MountPoint = "/cdrom"
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// Hostname is the filename in configPath where the hostname is stored
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Hostname = "hostname"
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// SSH is the path where sshd configuration from the provider is stored
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SSH = "ssh"
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// TODO(rneugeba): Need to check this is the same everywhere
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cdromDev = "/dev/sr0"
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)
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// Provider is a generic interface for metadata/userdata providers.
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type Provider interface {
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// Probe returns true if the provider was detected.
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Probe() bool
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// Extract user data. This may write some data, specific to a
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// provider, to ConfigPath and should return the generic userdata.
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Extract() ([]byte, error)
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}
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// netProviders is a list of Providers offering metadata/userdata over the network
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var netProviders []Provider
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// cdromProviders is a list of Providers offering metadata/userdata data via CDROM
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var cdromProviders []Provider
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func init() {
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netProviders = []Provider{NewGCP()}
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cdromProviders = []Provider{NewCDROM()}
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}
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func main() {
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if err := os.MkdirAll(ConfigPath, 0755); err != nil {
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log.Fatalf("Could not create %s: %s", ConfigPath, err)
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}
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var userdata []byte
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var err error
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found := false
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for _, p := range netProviders {
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if p.Probe() {
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userdata, err = p.Extract()
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found = true
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break
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}
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}
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if !found {
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log.Printf("Trying CDROM")
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if err := os.Mkdir(MountPoint, 0755); err != nil {
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log.Printf("CDROM: Failed to create %s: %s", MountPoint, err)
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goto ErrorOut
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}
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if err := mountCDROM(cdromDev, MountPoint); err != nil {
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log.Printf("Failed to mount cdrom: %s", err)
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goto ErrorOut
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}
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defer syscall.Unmount(MountPoint, 0)
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// Don't worry about removing MountPoint. We are in a container
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for _, p := range cdromProviders {
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if p.Probe() {
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userdata, err = p.Extract()
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found = true
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break
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}
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}
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}
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ErrorOut:
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if !found {
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log.Printf("No metadata/userdata found. Bye")
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return
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}
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if err != nil {
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log.Printf("Error during metadata probe: %s", err)
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}
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if userdata != nil {
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if err := processUserData(userdata); err != nil {
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log.Printf("Could not extract user data: %s", err)
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}
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}
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// Handle setting the hostname as a special case. We want to
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// do this early and don't really want another container for it.
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hostname, err := ioutil.ReadFile(path.Join(ConfigPath, Hostname))
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if err == nil {
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err := syscall.Sethostname(hostname)
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if err != nil {
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log.Printf("Failed to set hostname: %s", err)
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} else {
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log.Printf("Set hostname to: %s", string(hostname))
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}
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}
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}
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// If the userdata is a json file, create a directory/file hierarchy.
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// Example:
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// {
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// "foobar" : {
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// "foo" : {
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// "perm": "0644",
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// "content": "hello"
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// }
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// }
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// Will create foobar/foo with mode 0644 and content "hello"
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func processUserData(data []byte) error {
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// Always write the raw data to a file
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err := ioutil.WriteFile(path.Join(ConfigPath, "userdata"), data, 0644)
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if err != nil {
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log.Printf("Could not write userdata: %s", err)
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return err
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}
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var fd interface{}
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if err := json.Unmarshal(data, &fd); err != nil {
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// Userdata is no JSON, presumably...
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log.Printf("Could not unmarshall userdata: %s", err)
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// This is not an error
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return nil
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}
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cm := fd.(map[string]interface{})
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for d, val := range cm {
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dir := path.Join(ConfigPath, d)
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if err := os.Mkdir(dir, 0755); err != nil {
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log.Printf("Failed to create %s: %s", dir, err)
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continue
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}
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files := val.(map[string]interface{})
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for f, i := range files {
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fi := i.(map[string]interface{})
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if _, ok := fi["perm"]; !ok {
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log.Printf("No permission provided %s:%s", f, fi)
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continue
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}
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if _, ok := fi["content"]; !ok {
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log.Printf("No content provided %s:%s", f, fi)
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continue
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}
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c := fi["content"].(string)
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p, err := strconv.ParseUint(fi["perm"].(string), 8, 32)
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if err != nil {
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log.Printf("Failed to parse permission %s: %s", fi, err)
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continue
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}
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if err := ioutil.WriteFile(path.Join(dir, f), []byte(c), os.FileMode(p)); err != nil {
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log.Printf("Failed to write %s/%s: %s", dir, f, err)
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continue
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}
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}
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}
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return nil
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}
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// mountCDROM mounts a CDROM/DVD device under mountPoint
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func mountCDROM(device, mountPoint string) error {
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// We may need to poll a little for device ready
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return syscall.Mount(device, mountPoint, "iso9660", syscall.MS_RDONLY, "")
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}
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