[POA-2609] Add k8s and CRI sub-modules and function interfaces

[mudit-postman]

In this PR, we created basic interfaces and functions in K8s and CRI modules.

K8s Functions:

• NewKubeClient: Initalize the kube client, create a clientset object and open a event watcher for events.
• TearDown: Function to be called on program shutdown to close event watcher.
• GetPodContainerImages: Will be used to check if agent is running as sidecar
• GetMainContainerUUID: Fetches container UUID, used by CRI module to inspect container
• GetPodsInNode: Get the list of pods running in the node agent is running. Will be used to get list of existing pods on agent start up
• GetPodStatus: Get the health status, used by the go routine which will track health of pods where apidump is running.

CRI Functions:

• NewCRIClient: Initialize the runtimeService client, opens a GRPC connection to the CRI endpoint
• GetNetworkNamespace: Fetch network namespace for given container ID
• GetEnvVars: Fetch env vars for given container ID

Note: This PR have some other functions which were created initially but later removed in implementation PRs.

[mudit-postman]

For testing I have created a project which calls all the functions in a flow.
Output

root@mj-test:~/test# go run main.go postman-insights-agent-kxx85
[INFO] Pod Container Images: [public.ecr.aws/postman/postman-insights-agent:preview]
[INFO] Main Container UUID: <uuid>
[INFO] Pods in Node: [<nodes>]
[INFO] Pod Status: Running
[INFO] Stopping event watcher
[INFO] No CRI endpoint provided, trying default endpoints
[INFO] Network Namespace: <string>
[INFO] Environment Variables: <map[string]string>
root@mj-test:~/test#

Test code `main.go`

package main

import (
	"fmt"
	"os"

	"test-proj/cri_apis"
	"test-proj/kube_apis"

	"github.com/postmanlabs/postman-insights-agent/printer"
)

func k8s_funcs(podName string) (string, error) {
	// Initialize KubeClient
	kubeClient, err := kube_apis.NewKubeClient()
	if err != nil {
		return "", fmt.Errorf("failed to create KubeClient: %v", err)
	}
	defer kubeClient.TearDown()

	// GetPodContainerImages
	podImages, err := kubeClient.GetPodContainerImages(podName)
	if err != nil {
		return "", fmt.Errorf("failed to get pod container images: %v", err)
	}
	printer.Infof("Pod Container Images: %v\n", podImages)

	// GetMainContainerUUID
	containerUUID, err := kubeClient.GetMainContainerUUID(podName)
	if err != nil {
		return "", fmt.Errorf("failed to get main container UUID: %v", err)
	}
	printer.Infof("Main Container UUID: %s\n", containerUUID)

	// GetPodsInNode
	podNames, err := kubeClient.GetPodsInNode(kubeClient.AgentNode)
	if err != nil {
		return containerUUID, fmt.Errorf("failed to get pods in node: %v", err)
	}
	printer.Infof("Pods in Node: %v\n", podNames)

	// GetPodStatus
	podStatus, err := kubeClient.GetPodStatus(podName)
	if err != nil {
		return containerUUID, fmt.Errorf("failed to get pod status: %v", err)
	}
	printer.Infof("Pod Status: %s\n", podStatus)

	return containerUUID, nil
}

func cri_funcs(containerUUID string) error {
	// Initialize CriClient
	criClient, err := cri_apis.NewCRIClient("")
	if err != nil {
		return fmt.Errorf("failed to create CriClient: %v", err)
	}

	// GetNetworkNamespace
	networkNamespace, err := criClient.GetNetworkNamespace(containerUUID)
	if err != nil {
		return fmt.Errorf("failed to get network namespace: %v", err)
	}
	printer.Infof("Network Namespace: %s\n", networkNamespace)

	// GetEnvVars
	envVars, err := criClient.GetEnvVars(containerUUID)
	if err != nil {
		return fmt.Errorf("failed to get environment variables: %v", err)
	}
	printer.Infof("Environment Variables: %v\n", envVars)

	return nil
}

func main() {
	// Check if args are provided
	if len(os.Args) < 2 {
		printer.Errorln("Pod name not provided")
		return
	}
	podName := os.Args[1]

	// Call k8s_funcs
	containerUUID, err := k8s_funcs(podName)
	if err != nil {
		printer.Errorf("Error from k8s_funcs: %v\n", err)
	}

	// Call cri_funcs
	if containerUUID == "" {
		printer.Infoln("Container UUID not found, exiting...")
		return
	}
	err = cri_funcs(containerUUID)
	if err != nil {
		printer.Errorf("Error from cri_funcs: %v\n", err)
	}
}

[mgritter]

Looks like a good start, I would consider putting these in a subdirectory.