生成容器引用信息
基于kubernetes v1.18.6，关于基于windows平台运行kubelet的相关代码逻辑不作解析。
概述
kubelet通过以下四个步骤，来启动pod容器：
其中创建容器又分为以下子步骤：
本文主要解析创建容器/创建容器阶段kubelet所做工作，首先我们先看下创建容器阶段的代码逻辑
func (m *kubeGenericRuntimeManager) startContainer(podSandboxID string, podSandboxConfig *runtimeapi.PodSandboxConfig, spec *startSpec, pod *v1.Pod, podStatus *kubecontainer.PodStatus, pullSecrets []v1.Secret, podIP string, podIPs []string) (string, error) {
...
containerID, err := m.runtimeService.CreateContainer(podSandboxID, containerConfig, podSandboxConfig)
...
}
接下来我们分析m.runtimeService.CreateContainer()函数调用
m.runtimeService.CreateContainer()函数解析
流程解析
流程很简单：调用容器运行时创建容器，返回容器ID
入参:
- 沙箱
ID - 沙箱配置
- 容器元数据
返回值: 容器
ID、异常
源码解析
kubernetes\pkg\kubelet\remote\remote_runtime.go
func (r *RemoteRuntimeService) CreateContainer(podSandBoxID string, config *runtimeapi.ContainerConfig, sandboxConfig *runtimeapi.PodSandboxConfig) (string, error) {
ctx, cancel := getContextWithTimeout(r.timeout)
defer cancel()
resp, err := r.runtimeClient.CreateContainer(ctx, &runtimeapi.CreateContainerRequest{
PodSandboxId: podSandBoxID,
Config: config,
SandboxConfig: sandboxConfig,
})
if err != nil {
klog.Errorf("CreateContainer in sandbox %q from runtime service failed: %v", podSandBoxID, err)
return "", err
}
if resp.ContainerId == "" {
errorMessage := fmt.Sprintf("ContainerId is not set for container %q", config.GetMetadata())
klog.Errorf("CreateContainer failed: %s", errorMessage)
return "", errors.New(errorMessage)
}
return resp.ContainerId, nil
}
关于沙箱
前文我们了解到: kubelet通过调用容器运行时创建容器，返回容器ID。其中入参中有沙箱相关的参数。
那么沙箱到底是什么？
沙箱其实是CRI定义的。当运行时为docker时，sandbox实质就是pause容器。
pause容器作为一个pod内其他所有容器的父角色，拥有很多pod级别资源，如：
DNS配置、命名空间（主机名、IP地址、端口映射列表），父级控制组（pod内容器控制组的父控制组由pause容器定义）等
关于pause容器介绍，建议您移步The Almighty Pause Container
PodSandboxConfig沙箱配置对象数据结构解析
type PodSandboxConfig struct {
// Metadata of the sandbox. This information will uniquely identify the
// sandbox, and the runtime should leverage this to ensure correct
// operation. The runtime may also use this information to improve UX, such
// as by constructing a readable name.
Metadata *PodSandboxMetadata `protobuf:"bytes,1,opt,name=metadata,proto3" json:"metadata,omitempty"`
// Hostname of the sandbox. Hostname could only be empty when the pod
// network namespace is NODE.
Hostname string `protobuf:"bytes,2,opt,name=hostname,proto3" json:"hostname,omitempty"`
// Path to the directory on the host in which container log files are
// stored.
// By default the log of a container going into the LogDirectory will be
// hooked up to STDOUT and STDERR. However, the LogDirectory may contain
// binary log files with structured logging data from the individual
// containers. For example, the files might be newline separated JSON
// structured logs, systemd-journald journal files, gRPC trace files, etc.
// E.g.,
// PodSandboxConfig.LogDirectory = `/var/log/pods/<podUID>/`
// ContainerConfig.LogPath = `containerName/Instance#.log`
//
// WARNING: Log management and how kubelet should interface with the
// container logs are under active discussion in
// https://issues.k8s.io/24677. There *may* be future change of direction
// for logging as the discussion carries on.
LogDirectory string `protobuf:"bytes,3,opt,name=log_directory,json=logDirectory,proto3" json:"log_directory,omitempty"`
// DNS config for the sandbox.
DnsConfig *DNSConfig `protobuf:"bytes,4,opt,name=dns_config,json=dnsConfig,proto3" json:"dns_config,omitempty"`
// Port mappings for the sandbox.
PortMappings []*PortMapping `protobuf:"bytes,5,rep,name=port_mappings,json=portMappings,proto3" json:"port_mappings,omitempty"`
// Key-value pairs that may be used to scope and select individual resources.
Labels map[string]string `protobuf:"bytes,6,rep,name=labels,proto3" json:"labels,omitempty" protobuf_key:"bytes,1,opt,name=key,proto3" protobuf_val:"bytes,2,opt,name=value,proto3"`
// Unstructured key-value map that may be set by the kubelet to store and
// retrieve arbitrary metadata. This will include any annotations set on a
// pod through the Kubernetes API.
//
// Annotations MUST NOT be altered by the runtime; the annotations stored
// here MUST be returned in the PodSandboxStatus associated with the pod
// this PodSandboxConfig creates.
//
// In general, in order to preserve a well-defined interface between the
// kubelet and the container runtime, annotations SHOULD NOT influence
// runtime behaviour.
//
// Annotations can also be useful for runtime authors to experiment with
// new features that are opaque to the Kubernetes APIs (both user-facing
// and the CRI). Whenever possible, however, runtime authors SHOULD
// consider proposing new typed fields for any new features instead.
Annotations map[string]string `protobuf:"bytes,7,rep,name=annotations,proto3" json:"annotations,omitempty" protobuf_key:"bytes,1,opt,name=key,proto3" protobuf_val:"bytes,2,opt,name=value,proto3"`
// Optional configurations specific to Linux hosts.
Linux *LinuxPodSandboxConfig `protobuf:"bytes,8,opt,name=linux,proto3" json:"linux,omitempty"`
XXX_NoUnkeyedLiteral struct{} `json:"-"`
XXX_sizecache int32 `json:"-"`
}