daemon/health.go
package daemon // import "github.com/docker/docker/daemon"
import (
"bytes"
"context"
"fmt"
"runtime"
"strings"
"sync"
"time"
"github.com/containerd/log"
"github.com/docker/docker/api/types"
"github.com/docker/docker/api/types/backend"
"github.com/docker/docker/api/types/events"
"github.com/docker/docker/api/types/strslice"
"github.com/docker/docker/container"
)
const (
// Longest healthcheck probe output message to store. Longer messages will be truncated.
maxOutputLen = 4096
// Default interval between probe runs (from the end of the first to the start of the second).
// Also the time before the first probe.
defaultProbeInterval = 30 * time.Second
// The maximum length of time a single probe run should take. If the probe takes longer
// than this, the check is considered to have failed.
defaultProbeTimeout = 30 * time.Second
// The time given for the container to start before the health check starts considering
// the container unstable. Defaults to none.
defaultStartPeriod = 0 * time.Second
// defaultStartInterval is the default interval between health checks during
// the start period.
defaultStartInterval = 5 * time.Second
// Default number of consecutive failures of the health check
// for the container to be considered unhealthy.
defaultProbeRetries = 3
// Maximum number of entries to record
maxLogEntries = 5
)
const (
// Exit status codes that can be returned by the probe command.
exitStatusHealthy = 0 // Container is healthy
)
// probe implementations know how to run a particular type of probe.
type probe interface {
// Perform one run of the check. Returns the exit code and an optional
// short diagnostic string.
run(context.Context, *Daemon, *container.Container) (*types.HealthcheckResult, error)
}
// cmdProbe implements the "CMD" probe type.
type cmdProbe struct {
// Run the command with the system's default shell instead of execing it directly.
shell bool
}
// exec the healthcheck command in the container.
// Returns the exit code and probe output (if any)
func (p *cmdProbe) run(ctx context.Context, d *Daemon, cntr *container.Container) (*types.HealthcheckResult, error) {
startTime := time.Now()
cmdSlice := strslice.StrSlice(cntr.Config.Healthcheck.Test)[1:]
if p.shell {
cmdSlice = append(getShell(cntr), cmdSlice...)
}
entrypoint, args := d.getEntrypointAndArgs(strslice.StrSlice{}, cmdSlice)
execConfig := container.NewExecConfig(cntr)
execConfig.OpenStdin = false
execConfig.OpenStdout = true
execConfig.OpenStderr = true
execConfig.DetachKeys = []byte{}
execConfig.Entrypoint = entrypoint
execConfig.Args = args
execConfig.Tty = false
execConfig.Privileged = false
execConfig.User = cntr.Config.User
execConfig.WorkingDir = cntr.Config.WorkingDir
linkedEnv, err := d.setupLinkedContainers(cntr)
if err != nil {
return nil, err
}
execConfig.Env = container.ReplaceOrAppendEnvValues(cntr.CreateDaemonEnvironment(execConfig.Tty, linkedEnv), execConfig.Env)
d.registerExecCommand(cntr, execConfig)
d.LogContainerEventWithAttributes(cntr, events.Action(string(events.ActionExecCreate)+": "+execConfig.Entrypoint+" "+strings.Join(execConfig.Args, " ")), map[string]string{
"execID": execConfig.ID,
})
output := &limitedBuffer{}
probeCtx, cancelProbe := context.WithCancel(ctx)
defer cancelProbe()
execErr := make(chan error, 1)
options := backend.ExecStartConfig{
Stdout: output,
Stderr: output,
}
go func() { execErr <- d.ContainerExecStart(probeCtx, execConfig.ID, options) }()
// Starting an exec can take a significant amount of time: on the order
// of 1s in extreme cases. The time it takes dockerd and containerd to
// start the exec is time that the probe process is not running, and so
// should not count towards the health check's timeout. Apply a separate
// timeout to abort if the exec request is wedged.
tm := time.NewTimer(30 * time.Second)
defer tm.Stop()
select {
case <-tm.C:
return nil, fmt.Errorf("timed out starting health check for container %s", cntr.ID)
case err := <-execErr:
if err != nil {
return nil, err
}
case <-execConfig.Started:
healthCheckStartDuration.UpdateSince(startTime)
}
if !tm.Stop() {
<-tm.C
}
probeTimeout := timeoutWithDefault(cntr.Config.Healthcheck.Timeout, defaultProbeTimeout)
tm.Reset(probeTimeout)
select {
case <-tm.C:
cancelProbe()
log.G(ctx).WithContext(ctx).Debugf("Health check for container %s taking too long", cntr.ID)
// Wait for probe to exit (it might take some time to call containerd to kill
// the process and we don't want dying probes to pile up).
<-execErr
var msg string
if out := output.String(); len(out) > 0 {
msg = fmt.Sprintf("Health check exceeded timeout (%v): %s", probeTimeout, out)
} else {
msg = fmt.Sprintf("Health check exceeded timeout (%v)", probeTimeout)
}
return &types.HealthcheckResult{
ExitCode: -1,
Output: msg,
End: time.Now(),
}, nil
case err := <-execErr:
if err != nil {
return nil, err
}
}
info, err := d.getExecConfig(execConfig.ID)
if err != nil {
return nil, err
}
exitCode, err := func() (int, error) {
info.Lock()
defer info.Unlock()
if info.ExitCode == nil {
return 0, fmt.Errorf("healthcheck for container %s has no exit code", cntr.ID)
}
return *info.ExitCode, nil
}()
if err != nil {
return nil, err
}
// Note: Go's json package will handle invalid UTF-8 for us
out := output.String()
return &types.HealthcheckResult{
End: time.Now(),
ExitCode: exitCode,
Output: out,
}, nil
}
// Update the container's Status.Health struct based on the latest probe's result.
func handleProbeResult(d *Daemon, c *container.Container, result *types.HealthcheckResult, done chan struct{}) {
c.Lock()
defer c.Unlock()
// probe may have been cancelled while waiting on lock. Ignore result then
select {
case <-done:
return
default:
}
retries := c.Config.Healthcheck.Retries
if retries <= 0 {
retries = defaultProbeRetries
}
h := c.State.Health
oldStatus := h.Status()
if len(h.Log) >= maxLogEntries {
h.Log = append(h.Log[len(h.Log)+1-maxLogEntries:], result)
} else {
h.Log = append(h.Log, result)
}
if result.ExitCode == exitStatusHealthy {
h.FailingStreak = 0
h.SetStatus(types.Healthy)
} else { // Failure (including invalid exit code)
shouldIncrementStreak := true
// If the container is starting (i.e. we never had a successful health check)
// then we check if we are within the start period of the container in which
// case we do not increment the failure streak.
if h.Status() == types.Starting {
startPeriod := timeoutWithDefault(c.Config.Healthcheck.StartPeriod, defaultStartPeriod)
timeSinceStart := result.Start.Sub(c.State.StartedAt)
// If still within the start period, then don't increment failing streak.
if timeSinceStart < startPeriod {
shouldIncrementStreak = false
}
}
if shouldIncrementStreak {
h.FailingStreak++
if h.FailingStreak >= retries {
h.SetStatus(types.Unhealthy)
}
}
// Else we're starting or healthy. Stay in that state.
}
// Replicate Health status changes to the API, skipping persistent storage
// to avoid unnecessary disk writes. The health state is only best-effort
// persisted across of the daemon. It will get written to disk on the next
// checkpoint, such as when the container state changes.
if err := c.CommitInMemory(d.containersReplica); err != nil {
// queries will be inconsistent until the next probe runs or other state mutations
// checkpoint the container
log.G(context.TODO()).Errorf("Error replicating health state for container %s: %v", c.ID, err)
}
current := h.Status()
if oldStatus != current {
d.LogContainerEvent(c, events.Action(string(events.ActionHealthStatus)+": "+current))
}
}
// Run the container's monitoring thread until notified via "stop".
// There is never more than one monitor thread running per container at a time.
func monitor(d *Daemon, c *container.Container, stop chan struct{}, probe probe) {
probeInterval := timeoutWithDefault(c.Config.Healthcheck.Interval, defaultProbeInterval)
startInterval := timeoutWithDefault(c.Config.Healthcheck.StartInterval, defaultStartInterval)
startPeriod := timeoutWithDefault(c.Config.Healthcheck.StartPeriod, defaultStartPeriod)
c.Lock()
started := c.State.StartedAt
c.Unlock()
getInterval := func() time.Duration {
if time.Since(started) >= startPeriod {
return probeInterval
}
c.Lock()
status := c.Health.Health.Status
c.Unlock()
if status == types.Starting {
return startInterval
}
return probeInterval
}
intervalTimer := time.NewTimer(getInterval())
defer intervalTimer.Stop()
for {
select {
case <-stop:
log.G(context.TODO()).Debugf("Stop healthcheck monitoring for container %s (received while idle)", c.ID)
return
case <-intervalTimer.C:
log.G(context.TODO()).Debugf("Running health check for container %s ...", c.ID)
startTime := time.Now()
ctx, cancelProbe := context.WithCancel(context.Background())
results := make(chan *types.HealthcheckResult, 1)
go func() {
healthChecksCounter.Inc()
result, err := probe.run(ctx, d, c)
if err != nil {
healthChecksFailedCounter.Inc()
log.G(ctx).Warnf("Health check for container %s error: %v", c.ID, err)
results <- &types.HealthcheckResult{
ExitCode: -1,
Output: err.Error(),
Start: startTime,
End: time.Now(),
}
} else {
result.Start = startTime
log.G(ctx).Debugf("Health check for container %s done (exitCode=%d)", c.ID, result.ExitCode)
results <- result
}
close(results)
}()
select {
case <-stop:
log.G(ctx).Debugf("Stop healthcheck monitoring for container %s (received while probing)", c.ID)
cancelProbe()
// Wait for probe to exit (it might take a while to respond to the TERM
// signal and we don't want dying probes to pile up).
<-results
return
case result := <-results:
handleProbeResult(d, c, result, stop)
cancelProbe()
}
}
intervalTimer.Reset(getInterval())
}
}
// Get a suitable probe implementation for the container's healthcheck configuration.
// Nil will be returned if no healthcheck was configured or NONE was set.
func getProbe(c *container.Container) probe {
config := c.Config.Healthcheck
if config == nil || len(config.Test) == 0 {
return nil
}
switch config.Test[0] {
case "CMD":
return &cmdProbe{shell: false}
case "CMD-SHELL":
return &cmdProbe{shell: true}
case "NONE":
return nil
default:
log.G(context.TODO()).Warnf("Unknown healthcheck type '%s' (expected 'CMD') in container %s", config.Test[0], c.ID)
return nil
}
}
// Ensure the health-check monitor is running or not, depending on the current
// state of the container.
// Called from monitor.go, with c locked.
func (daemon *Daemon) updateHealthMonitor(c *container.Container) {
h := c.State.Health
if h == nil {
return // No healthcheck configured
}
probe := getProbe(c)
wantRunning := c.Running && !c.Paused && probe != nil
if wantRunning {
if stop := h.OpenMonitorChannel(); stop != nil {
go monitor(daemon, c, stop, probe)
}
} else {
h.CloseMonitorChannel()
}
}
// Reset the health state for a newly-started, restarted or restored container.
// initHealthMonitor is called from monitor.go and we should never be running
// two instances at once.
// Called with c locked.
func (daemon *Daemon) initHealthMonitor(c *container.Container) {
// If no healthcheck is setup then don't init the monitor
if getProbe(c) == nil {
return
}
// This is needed in case we're auto-restarting
daemon.stopHealthchecks(c)
if h := c.State.Health; h != nil {
h.SetStatus(types.Starting)
h.FailingStreak = 0
} else {
h := &container.Health{}
h.SetStatus(types.Starting)
c.State.Health = h
}
daemon.updateHealthMonitor(c)
}
// Called when the container is being stopped (whether because the health check is
// failing or for any other reason).
func (daemon *Daemon) stopHealthchecks(c *container.Container) {
h := c.State.Health
if h != nil {
h.CloseMonitorChannel()
}
}
// Buffer up to maxOutputLen bytes. Further data is discarded.
type limitedBuffer struct {
buf bytes.Buffer
mu sync.Mutex
truncated bool // indicates that data has been lost
}
// Append to limitedBuffer while there is room.
func (b *limitedBuffer) Write(data []byte) (int, error) {
b.mu.Lock()
defer b.mu.Unlock()
bufLen := b.buf.Len()
dataLen := len(data)
keep := minInt(maxOutputLen-bufLen, dataLen)
if keep > 0 {
b.buf.Write(data[:keep])
}
if keep < dataLen {
b.truncated = true
}
return dataLen, nil
}
// The contents of the buffer, with "..." appended if it overflowed.
func (b *limitedBuffer) String() string {
b.mu.Lock()
defer b.mu.Unlock()
out := b.buf.String()
if b.truncated {
out = out + "..."
}
return out
}
// If configuredValue is zero, use defaultValue instead.
func timeoutWithDefault(configuredValue time.Duration, defaultValue time.Duration) time.Duration {
if configuredValue == 0 {
return defaultValue
}
return configuredValue
}
func minInt(x, y int) int {
if x < y {
return x
}
return y
}
func getShell(cntr *container.Container) []string {
if len(cntr.Config.Shell) != 0 {
return cntr.Config.Shell
}
if runtime.GOOS != "windows" {
return []string{"/bin/sh", "-c"}
}
if cntr.OS != runtime.GOOS {
return []string{"/bin/sh", "-c"}
}
return []string{"cmd", "/S", "/C"}
}