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k8s 原生并不反对就地降级。诸如 deployment 等工作负载在降级的过程中，间接对 Pod 进行recreate。
实现容器的就地降级的另外一个前提是 kubelet 通过容器 hash 来治理容器版本。
当创立一个 Pod 的时候，kubelet 会计算每个容器的 hash，并且把该 hash 值写到 ContainerStatus 中，该 status 的定义如下：
// Status represents the status of a container.
type Status struct {
// ID of the container.
ID ContainerID
// Name of the container.
Name string
// Status of the container.
State State
// Creation time of the container.
CreatedAt time.Time
// Start time of the container.
StartedAt time.Time
// Finish time of the container.
FinishedAt time.Time
// Exit code of the container.
ExitCode int
// Name of the image, this also includes the tag of the image,
// the expected form is "NAME:TAG".
Image string
// ID of the image.
ImageID string
// Hash of the container, used for comparison.
Hash uint64
// Number of times that the container has been restarted.
RestartCount int
// A string explains why container is in such a status.
Reason string
// Message written by the container before exiting (stored in
// TerminationMessagePath).
Message string
}其中的Hashfiled 正是咱们明天讲到的 hash。
如果 spec.containers[i].image 发生变化之后，kubelet 通过计算 hash 值，判断出容器版本曾经变动，须要执行降级操作，拉取新的 image，重启该容器，重启胜利之后，会把新的 hash 写到下面讲的 ContainerStatus 中。
kubelet 源码中提供了一个计算容器 hash 的辅助办法：
// HashContainer returns the hash of the container. It is used to compare
// the running container with its desired spec.
// Note: remember to update hashValues in container_hash_test.go as well.
func HashContainer(container *v1.Container) uint64 {hash := fnv.New32a()
// Omit nil or empty field when calculating hash value
// Please see https://github.com/kubernetes/kubernetes/issues/53644
containerJSON, _ := json.Marshal(container)
hashutil.DeepHashObject(hash, containerJSON)
return uint64(hash.Sum32())
}该办法，实现了容器 hash 的计算。
kubelet 通过 hash，比拟理论运行的容器和 spec 中冀望的容器，判断是否容器曾经扭转，具体代码如下：
func containerChanged(container *v1.Container, containerStatus *kubecontainer.Status) (uint64, uint64, bool) {expectedHash := kubecontainer.HashContainer(container)
return expectedHash, containerStatus.Hash, containerStatus.Hash != expectedHash
}如果曾经变动，则会执行重启操作。
restart := shouldRestartOnFailure(pod)
if _, _, changed := containerChanged(&container, containerStatus); changed {message = fmt.Sprintf("Container %s definition changed", container.Name)
// Restart regardless of the restart policy because the container
// spec changed.
restart = true
}而后就实现了就地降级。
上述的逻辑位于 kuberuntime_manager.go 文件 SyncPod 办法中。该文件是 kubelet 的 kuberuntimeManager 的实现。
// SyncPod syncs the running pod into the desired pod by executing following steps:
//
// 1. Compute sandbox and container changes.
// 2. Kill pod sandbox if necessary.
// 3. Kill any containers that should not be running.
// 4. Create sandbox if necessary.
// 5. Create ephemeral containers.
// 6. Create init containers.
// 7. Create normal containers.
func (m *kubeGenericRuntimeManager) SyncPod(pod *v1.Pod, podStatus *kubecontainer.PodStatus, pullSecrets []v1.Secret, backOff *flowcontrol.Backoff) (result kubecontainer.PodSyncResult) {
// Step 1: Compute sandbox and container changes.
podContainerChanges := m.computePodActions(pod, podStatus)
klog.V(3).Infof("computePodActions got %+v for pod %q", podContainerChanges, format.Pod(pod))
if podContainerChanges.CreateSandbox {ref, err := ref.GetReference(legacyscheme.Scheme, pod)
if err != nil {klog.Errorf("Couldn't make a ref to pod %q: '%v'", format.Pod(pod), err)
}
if podContainerChanges.SandboxID != "" {m.recorder.Eventf(ref, v1.EventTypeNormal, events.SandboxChanged, "Pod sandbox changed, it will be killed and re-created.")
} else {klog.V(4).Infof("SyncPod received new pod %q, will create a sandbox for it", format.Pod(pod))
}
}
// Step 2: Kill the pod if the sandbox has changed.
if podContainerChanges.KillPod {
if podContainerChanges.CreateSandbox {klog.V(4).Infof("Stopping PodSandbox for %q, will start new one", format.Pod(pod))
} else {klog.V(4).Infof("Stopping PodSandbox for %q because all other containers are dead.", format.Pod(pod))
}
killResult := m.killPodWithSyncResult(pod, kubecontainer.ConvertPodStatusToRunningPod(m.runtimeName, podStatus), nil)
result.AddPodSyncResult(killResult)
if killResult.Error() != nil {klog.Errorf("killPodWithSyncResult failed: %v", killResult.Error())
return
}
if podContainerChanges.CreateSandbox {m.purgeInitContainers(pod, podStatus)
}
} else {
// Step 3: kill any running containers in this pod which are not to keep.
for containerID, containerInfo := range podContainerChanges.ContainersToKill {klog.V(3).Infof("Killing unwanted container %q(id=%q) for pod %q", containerInfo.name, containerID, format.Pod(pod))
killContainerResult := kubecontainer.NewSyncResult(kubecontainer.KillContainer, containerInfo.name)
result.AddSyncResult(killContainerResult)
if err := m.killContainer(pod, containerID, containerInfo.name, containerInfo.message, nil); err != nil {killContainerResult.Fail(kubecontainer.ErrKillContainer, err.Error())
klog.Errorf("killContainer %q(id=%q) for pod %q failed: %v", containerInfo.name, containerID, format.Pod(pod), err)
return
}
}
}
// Keep terminated init containers fairly aggressively controlled
// This is an optimization because container removals are typically handled
// by container garbage collector.
m.pruneInitContainersBeforeStart(pod, podStatus)
// We pass the value of the PRIMARY podIP and list of podIPs down to
// generatePodSandboxConfig and generateContainerConfig, which in turn
// passes it to various other functions, in order to facilitate functionality
// that requires this value (hosts file and downward API) and avoid races determining
// the pod IP in cases where a container requires restart but the
// podIP isn't in the status manager yet. The list of podIPs is used to
// generate the hosts file.
//
// We default to the IPs in the passed-in pod status, and overwrite them if the
// sandbox needs to be (re)started.
var podIPs []string
if podStatus != nil {podIPs = podStatus.IPs}
// Step 4: Create a sandbox for the pod if necessary.
podSandboxID := podContainerChanges.SandboxID
if podContainerChanges.CreateSandbox {
var msg string
var err error
klog.V(4).Infof("Creating PodSandbox for pod %q", format.Pod(pod))
createSandboxResult := kubecontainer.NewSyncResult(kubecontainer.CreatePodSandbox, format.Pod(pod))
result.AddSyncResult(createSandboxResult)
podSandboxID, msg, err = m.createPodSandbox(pod, podContainerChanges.Attempt)
if err != nil {createSandboxResult.Fail(kubecontainer.ErrCreatePodSandbox, msg)
klog.Errorf("createPodSandbox for pod %q failed: %v", format.Pod(pod), err)
ref, referr := ref.GetReference(legacyscheme.Scheme, pod)
if referr != nil {klog.Errorf("Couldn't make a ref to pod %q: '%v'", format.Pod(pod), referr)
}
m.recorder.Eventf(ref, v1.EventTypeWarning, events.FailedCreatePodSandBox, "Failed to create pod sandbox: %v", err)
return
}
klog.V(4).Infof("Created PodSandbox %q for pod %q", podSandboxID, format.Pod(pod))
podSandboxStatus, err := m.runtimeService.PodSandboxStatus(podSandboxID)
if err != nil {ref, referr := ref.GetReference(legacyscheme.Scheme, pod)
if referr != nil {klog.Errorf("Couldn't make a ref to pod %q: '%v'", format.Pod(pod), referr)
}
m.recorder.Eventf(ref, v1.EventTypeWarning, events.FailedStatusPodSandBox, "Unable to get pod sandbox status: %v", err)
klog.Errorf("Failed to get pod sandbox status: %v; Skipping pod %q", err, format.Pod(pod))
result.Fail(err)
return
}
// If we ever allow updating a pod from non-host-network to
// host-network, we may use a stale IP.
if !kubecontainer.IsHostNetworkPod(pod) {
// Overwrite the podIPs passed in the pod status, since we just started the pod sandbox.
podIPs = m.determinePodSandboxIPs(pod.Namespace, pod.Name, podSandboxStatus)
klog.V(4).Infof("Determined the ip %v for pod %q after sandbox changed", podIPs, format.Pod(pod))
}
}
// the start containers routines depend on pod ip(as in primary pod ip)
// instead of trying to figure out if we have 0 < len(podIPs)
// everytime, we short circuit it here
podIP := ""
if len(podIPs) != 0 {podIP = podIPs[0]
}
// Get podSandboxConfig for containers to start.
configPodSandboxResult := kubecontainer.NewSyncResult(kubecontainer.ConfigPodSandbox, podSandboxID)
result.AddSyncResult(configPodSandboxResult)
podSandboxConfig, err := m.generatePodSandboxConfig(pod, podContainerChanges.Attempt)
if err != nil {message := fmt.Sprintf("GeneratePodSandboxConfig for pod %q failed: %v", format.Pod(pod), err)
klog.Error(message)
configPodSandboxResult.Fail(kubecontainer.ErrConfigPodSandbox, message)
return
}
// Helper containing boilerplate common to starting all types of containers.
// typeName is a label used to describe this type of container in log messages,
// currently: "container", "init container" or "ephemeral container"
start := func(typeName string, spec *startSpec) error {startContainerResult := kubecontainer.NewSyncResult(kubecontainer.StartContainer, spec.container.Name)
result.AddSyncResult(startContainerResult)
isInBackOff, msg, err := m.doBackOff(pod, spec.container, podStatus, backOff)
if isInBackOff {startContainerResult.Fail(err, msg)
klog.V(4).Infof("Backing Off restarting %v %+v in pod %v", typeName, spec.container, format.Pod(pod))
return err
}
klog.V(4).Infof("Creating %v %+v in pod %v", typeName, spec.container, format.Pod(pod))
// NOTE (aramase) podIPs are populated for single stack and dual stack clusters. Send only podIPs.
if msg, err := m.startContainer(podSandboxID, podSandboxConfig, spec, pod, podStatus, pullSecrets, podIP, podIPs); err != nil {startContainerResult.Fail(err, msg)
// known errors that are logged in other places are logged at higher levels here to avoid
// repetitive log spam
switch {
case err == images.ErrImagePullBackOff:
klog.V(3).Infof("%v %+v start failed in pod %v: %v: %s", typeName, spec.container, format.Pod(pod), err, msg)
default:
utilruntime.HandleError(fmt.Errorf("%v %+v start failed in pod %v: %v: %s", typeName, spec.container, format.Pod(pod), err, msg))
}
return err
}
return nil
}
// Step 5: start ephemeral containers
// These are started "prior" to init containers to allow running ephemeral containers even when there
// are errors starting an init container. In practice init containers will start first since ephemeral
// containers cannot be specified on pod creation.
if utilfeature.DefaultFeatureGate.Enabled(features.EphemeralContainers) {
for _, idx := range podContainerChanges.EphemeralContainersToStart {start("ephemeral container", ephemeralContainerStartSpec(&pod.Spec.EphemeralContainers[idx]))
}
}
// Step 6: start the init container.
if container := podContainerChanges.NextInitContainerToStart; container != nil {
// Start the next init container.
if err := start("init container", containerStartSpec(container)); err != nil {return}
// Successfully started the container; clear the entry in the failure
klog.V(4).Infof("Completed init container %q for pod %q", container.Name, format.Pod(pod))
}
// Step 7: start containers in podContainerChanges.ContainersToStart.
for _, idx := range podContainerChanges.ContainersToStart {start("container", containerStartSpec(&pod.Spec.Containers[idx]))
}
return
}公布于 4 小时前
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