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exec_linux.go
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exec_linux.go
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package executor
import (
"bytes"
"encoding/json"
"errors"
"fmt"
"io"
"os"
"os/exec"
"os/user"
"path/filepath"
"strconv"
"strings"
"syscall"
"github.com/hashicorp/go-multierror"
"github.com/hashicorp/nomad/client/allocdir"
"github.com/hashicorp/nomad/client/driver/args"
"github.com/hashicorp/nomad/client/driver/environment"
"github.com/hashicorp/nomad/command"
"github.com/hashicorp/nomad/helper/discover"
"github.com/hashicorp/nomad/nomad/structs"
cgroupFs "github.com/opencontainers/runc/libcontainer/cgroups/fs"
cgroupConfig "github.com/opencontainers/runc/libcontainer/configs"
)
const (
cgroupMount = "/sys/fs/cgroup"
)
var (
// A mapping of directories on the host OS to attempt to embed inside each
// task's chroot.
chrootEnv = map[string]string{
"/bin": "/bin",
"/etc": "/etc",
"/lib": "/lib",
"/lib32": "/lib32",
"/lib64": "/lib64",
"/usr/bin": "/usr/bin",
"/usr/lib": "/usr/lib",
}
)
func NewExecutor() Executor {
e := LinuxExecutor{}
// TODO: In a follow-up PR make it so this only happens once per client.
// Fingerprinting shouldn't happen per task.
// Check that cgroups are available.
if _, err := os.Stat(cgroupMount); err == nil {
e.cgroupEnabled = true
}
return &e
}
// Linux executor is designed to run on linux kernel 2.8+.
type LinuxExecutor struct {
cmd
user *user.User
// Finger print capabilities.
cgroupEnabled bool
// Isolation configurations.
groups *cgroupConfig.Cgroup
alloc *allocdir.AllocDir
taskName string
taskDir string
// Tracking of child process.
spawnChild exec.Cmd
spawnOutputWriter *os.File
spawnOutputReader *os.File
// Track whether there are filesystems mounted in the task dir.
mounts bool
}
func (e *LinuxExecutor) Limit(resources *structs.Resources) error {
if resources == nil {
return errNoResources
}
if e.cgroupEnabled {
e.configureCgroups(resources)
}
return nil
}
func (e *LinuxExecutor) ConfigureTaskDir(taskName string, alloc *allocdir.AllocDir) error {
e.taskName = taskName
taskDir, ok := alloc.TaskDirs[taskName]
if !ok {
fmt.Errorf("Couldn't find task directory for task %v", taskName)
}
e.taskDir = taskDir
if err := alloc.MountSharedDir(taskName); err != nil {
return err
}
if err := alloc.Embed(taskName, chrootEnv); err != nil {
return err
}
// Mount dev
dev := filepath.Join(taskDir, "dev")
if err := os.Mkdir(dev, 0777); err != nil {
return fmt.Errorf("Mkdir(%v) failed: %v", dev)
}
if err := syscall.Mount("", dev, "devtmpfs", syscall.MS_RDONLY, ""); err != nil {
return fmt.Errorf("Couldn't mount /dev to %v: %v", dev, err)
}
// Mount proc
proc := filepath.Join(taskDir, "proc")
if err := os.Mkdir(proc, 0777); err != nil {
return fmt.Errorf("Mkdir(%v) failed: %v", proc)
}
if err := syscall.Mount("", proc, "proc", syscall.MS_RDONLY, ""); err != nil {
return fmt.Errorf("Couldn't mount /proc to %v: %v", proc, err)
}
// Set the tasks AllocDir environment variable.
env, err := environment.ParseFromList(e.Cmd.Env)
if err != nil {
return err
}
env.SetAllocDir(filepath.Join("/", allocdir.SharedAllocName))
e.Cmd.Env = env.List()
e.alloc = alloc
e.mounts = true
return nil
}
func (e *LinuxExecutor) cleanTaskDir() error {
if e.alloc == nil {
return errors.New("ConfigureTaskDir() must be called before Start()")
}
if !e.mounts {
return nil
}
// Unmount dev.
errs := new(multierror.Error)
dev := filepath.Join(e.taskDir, "dev")
if err := syscall.Unmount(dev, 0); err != nil {
errs = multierror.Append(errs, fmt.Errorf("Failed to unmount dev (%v): %v", dev, err))
}
// Unmount proc.
proc := filepath.Join(e.taskDir, "proc")
if err := syscall.Unmount(proc, 0); err != nil {
errs = multierror.Append(errs, fmt.Errorf("Failed to unmount proc (%v): %v", proc, err))
}
e.mounts = false
return errs.ErrorOrNil()
}
func (e *LinuxExecutor) configureCgroups(resources *structs.Resources) {
if !e.cgroupEnabled {
return
}
e.groups = &cgroupConfig.Cgroup{}
// Groups will be created in a heiarchy according to the resource being
// constrained, current session, and then this unique name. Restraints are
// then placed in the corresponding files.
// Ex: restricting a process to 2048Mhz CPU and 2MB of memory:
// $ cat /sys/fs/cgroup/cpu/user/1000.user/4.session/<uuid>/cpu.shares
// 2028
// $ cat /sys/fs/cgroup/memory/user/1000.user/4.session/<uuid>/memory.limit_in_bytes
// 2097152
e.groups.Name = structs.GenerateUUID()
// TODO: verify this is needed for things like network access
e.groups.AllowAllDevices = true
if resources.MemoryMB > 0 {
// Total amount of memory allowed to consume
e.groups.Memory = int64(resources.MemoryMB * 1024 * 1024)
// Disable swap to avoid issues on the machine
e.groups.MemorySwap = int64(-1)
}
if resources.CPU > 0.0 {
// Set the relative CPU shares for this cgroup.
// The simplest scale is 1 share to 1 MHz so 1024 = 1GHz. This means any
// given process will have at least that amount of resources, but likely
// more since it is (probably) rare that the machine will run at 100%
// CPU. This scale will cease to work if a node is overprovisioned.
e.groups.CpuShares = int64(resources.CPU)
}
if resources.IOPS > 0 {
e.groups.BlkioThrottleReadIOpsDevice = strconv.FormatInt(int64(resources.IOPS), 10)
e.groups.BlkioThrottleWriteIOpsDevice = strconv.FormatInt(int64(resources.IOPS), 10)
}
}
func (e *LinuxExecutor) runAs(userid string) error {
errs := new(multierror.Error)
// First, try to lookup the user by uid
u, err := user.LookupId(userid)
if err == nil {
e.user = u
return nil
} else {
errs = multierror.Append(errs, err)
}
// Lookup failed, so try by username instead
u, err = user.Lookup(userid)
if err == nil {
e.user = u
return nil
} else {
errs = multierror.Append(errs, err)
}
// If we got here we failed to lookup based on id and username, so we'll
// return those errors.
return fmt.Errorf("Failed to identify user to run as: %s", errs)
}
func (e *LinuxExecutor) Start() error {
// Run as "nobody" user so we don't leak root privilege to the
// spawned process.
if err := e.runAs("nobody"); err == nil && e.user != nil {
e.cmd.SetUID(e.user.Uid)
e.cmd.SetGID(e.user.Gid)
}
if e.alloc == nil {
return errors.New("ConfigureTaskDir() must be called before Start()")
}
// Parse the commands arguments and replace instances of Nomad environment
// variables.
envVars, err := environment.ParseFromList(e.Cmd.Env)
if err != nil {
return err
}
combined := strings.Join(e.Cmd.Args, " ")
parsed, err := args.ParseAndReplace(combined, envVars.Map())
if err != nil {
return err
}
e.Cmd.Args = parsed
return e.spawnDaemon()
}
// spawnDaemon executes a double fork to start the user command with proper
// isolation. Stores the child process for use in Wait.
func (e *LinuxExecutor) spawnDaemon() error {
bin, err := discover.NomadExecutable()
if err != nil {
return fmt.Errorf("Failed to determine the nomad executable: %v", err)
}
// Serialize the cmd and the cgroup configuration so it can be passed to the
// sub-process.
var buffer bytes.Buffer
enc := json.NewEncoder(&buffer)
c := command.DaemonConfig{
Cmd: e.cmd.Cmd,
Chroot: e.taskDir,
StdoutFile: filepath.Join(e.taskDir, allocdir.TaskLocal, fmt.Sprintf("%v.stdout", e.taskName)),
StderrFile: filepath.Join(e.taskDir, allocdir.TaskLocal, fmt.Sprintf("%v.stderr", e.taskName)),
StdinFile: "/dev/null",
}
if err := enc.Encode(c); err != nil {
return fmt.Errorf("Failed to serialize daemon configuration: %v", err)
}
// Create a pipe to capture Stdout.
pr, pw, err := os.Pipe()
if err != nil {
return err
}
e.spawnOutputWriter = pw
e.spawnOutputReader = pr
// Call ourselves using a hidden flag. The new instance of nomad will join
// the passed cgroup, forkExec the cmd, and output status codes through
// Stdout.
escaped := strconv.Quote(buffer.String())
spawn := exec.Command(bin, "spawn-daemon", escaped)
spawn.Stdout = e.spawnOutputWriter
// Capture its Stdin.
spawnStdIn, err := spawn.StdinPipe()
if err != nil {
return err
}
if err := spawn.Start(); err != nil {
fmt.Errorf("Failed to call spawn-daemon on nomad executable: %v", err)
}
// Join the spawn-daemon to the cgroup.
if e.groups != nil {
manager := cgroupFs.Manager{}
manager.Cgroups = e.groups
// Apply will place the current pid into the tasks file for each of the
// created cgroups:
// /sys/fs/cgroup/memory/user/1000.user/4.session/<uuid>/tasks
//
// Apply requires superuser permissions, and may fail if Nomad is not run with
// the required permissions
if err := manager.Apply(spawn.Process.Pid); err != nil {
errs := new(multierror.Error)
errs = multierror.Append(errs, fmt.Errorf("Failed to join spawn-daemon to the cgroup (config => %+v): %v", manager.Cgroups, err))
if err := sendAbortCommand(spawnStdIn); err != nil {
errs = multierror.Append(errs, err)
}
return errs
}
}
// Tell it to start.
if err := sendStartCommand(spawnStdIn); err != nil {
return err
}
// Parse the response.
dec := json.NewDecoder(e.spawnOutputReader)
var resp command.SpawnStartStatus
if err := dec.Decode(&resp); err != nil {
return fmt.Errorf("Failed to parse spawn-daemon start response: %v", err)
}
if resp.ErrorMsg != "" {
return fmt.Errorf("Failed to execute user command: %s", resp.ErrorMsg)
}
e.spawnChild = *spawn
return nil
}
func sendStartCommand(w io.Writer) error {
enc := json.NewEncoder(w)
if err := enc.Encode(true); err != nil {
return fmt.Errorf("Failed to serialize start command: %v", err)
}
return nil
}
func sendAbortCommand(w io.Writer) error {
enc := json.NewEncoder(w)
if err := enc.Encode(false); err != nil {
return fmt.Errorf("Failed to serialize abort command: %v", err)
}
return nil
}
// Open's behavior is to kill all processes associated with the id and return an
// error. This is done because it is not possible to re-attach to the
// spawn-daemon's stdout to retrieve status messages.
func (e *LinuxExecutor) Open(id string) error {
parts := strings.SplitN(id, ":", 2)
if len(parts) != 2 {
return fmt.Errorf("Invalid id: %v", id)
}
switch parts[0] {
case "PID":
pid, err := strconv.Atoi(parts[1])
if err != nil {
return fmt.Errorf("Invalid id: failed to parse pid %v", parts[1])
}
process, err := os.FindProcess(pid)
if err != nil {
return fmt.Errorf("Failed to find Pid %v: %v", pid, err)
}
if err := process.Kill(); err != nil {
return fmt.Errorf("Failed to kill Pid %v: %v", pid, err)
}
case "CGROUP":
if !e.cgroupEnabled {
return errors.New("Passed a a cgroup identifier, but cgroups are disabled")
}
// De-serialize the cgroup configuration.
dec := json.NewDecoder(strings.NewReader(parts[1]))
var groups cgroupConfig.Cgroup
if err := dec.Decode(&groups); err != nil {
return fmt.Errorf("Failed to parse cgroup configuration: %v", err)
}
e.groups = &groups
if err := e.destroyCgroup(); err != nil {
return err
}
// TODO: cleanTaskDir is a little more complicated here because the OS
// may have already unmounted in the case of a restart. Need to scan.
default:
return fmt.Errorf("Invalid id type: %v", parts[0])
}
return errors.New("Could not re-open to id (intended).")
}
func (e *LinuxExecutor) Wait() error {
if e.spawnChild.Process == nil {
return errors.New("Can not find child to wait on")
}
defer e.spawnOutputWriter.Close()
defer e.spawnOutputReader.Close()
errs := new(multierror.Error)
if err := e.spawnChild.Wait(); err != nil {
errs = multierror.Append(errs, fmt.Errorf("Wait failed on pid %v: %v", e.spawnChild.Process.Pid, err))
}
// If they fork/exec and then exit, wait will return but they will be still
// running processes so we need to kill the full cgroup.
if e.groups != nil {
if err := e.destroyCgroup(); err != nil {
errs = multierror.Append(errs, err)
}
}
if err := e.cleanTaskDir(); err != nil {
errs = multierror.Append(errs, err)
}
return errs.ErrorOrNil()
}
// If cgroups are used, the ID is the cgroup structurue. Otherwise, it is the
// PID of the spawn-daemon process. An error is returned if the process was
// never started.
func (e *LinuxExecutor) ID() (string, error) {
if e.spawnChild.Process != nil {
if e.cgroupEnabled && e.groups != nil {
// Serialize the cgroup structure so it can be undone on suabsequent
// opens.
var buffer bytes.Buffer
enc := json.NewEncoder(&buffer)
if err := enc.Encode(e.groups); err != nil {
return "", fmt.Errorf("Failed to serialize daemon configuration: %v", err)
}
return fmt.Sprintf("CGROUP:%v", buffer.String()), nil
}
return fmt.Sprintf("PID:%d", e.spawnChild.Process.Pid), nil
}
return "", fmt.Errorf("Process has finished or was never started")
}
func (e *LinuxExecutor) Shutdown() error {
return e.ForceStop()
}
func (e *LinuxExecutor) ForceStop() error {
if e.spawnOutputReader != nil {
e.spawnOutputReader.Close()
}
if e.spawnOutputWriter != nil {
e.spawnOutputWriter.Close()
}
// If the task is not running inside a cgroup then just the spawn-daemon child is killed.
// TODO: Find a good way to kill the children of the spawn-daemon.
if e.groups == nil {
if err := e.spawnChild.Process.Kill(); err != nil {
return fmt.Errorf("Failed to kill child (%v): %v", e.spawnChild.Process.Pid, err)
}
return nil
}
errs := new(multierror.Error)
if e.groups != nil {
if err := e.destroyCgroup(); err != nil {
errs = multierror.Append(errs, err)
}
}
if err := e.cleanTaskDir(); err != nil {
errs = multierror.Append(errs, err)
}
return errs.ErrorOrNil()
}
func (e *LinuxExecutor) destroyCgroup() error {
if e.groups == nil {
return errors.New("Can't destroy: cgroup configuration empty")
}
manager := cgroupFs.Manager{}
manager.Cgroups = e.groups
pids, err := manager.GetPids()
if err != nil {
return fmt.Errorf("Failed to get pids in the cgroup %v: %v", e.groups.Name, err)
}
errs := new(multierror.Error)
for _, pid := range pids {
process, err := os.FindProcess(pid)
if err != nil {
multierror.Append(errs, fmt.Errorf("Failed to find Pid %v: %v", pid, err))
continue
}
if err := process.Kill(); err != nil {
multierror.Append(errs, fmt.Errorf("Failed to kill Pid %v: %v", pid, err))
continue
}
}
// Remove the cgroup.
if err := manager.Destroy(); err != nil {
multierror.Append(errs, fmt.Errorf("Failed to delete the cgroup directories: %v", err))
}
if len(errs.Errors) != 0 {
return fmt.Errorf("Failed to destroy cgroup: %v", errs)
}
return nil
}
func (e *LinuxExecutor) Command() *cmd {
return &e.cmd
}