Deep Dive: How Meta Trains Junior Engineers on Go 1.24 and Kubernetes 1.32

// Copyright 2024 Meta Platforms, Inc.
// SPDX-License-Identifier: Apache-2.0
// Training Lab Exercise 3: Arena Allocator Usage for High-Throughput Log Processing
// Junior engineers must modify this code to reduce GC pause time for 100k req/s log streams
package main

import (
    "arena"
    "bufio"
    "errors"
    "fmt"
    "log"
    "os"
    "strconv"
    "strings"
    "time"
)

// LogEntry represents a structured training exercise log from junior engineer sandbox environments
type LogEntry struct {
    Timestamp time.Time
    EngineerID string
    ExerciseID string
    Score      int
    ErrorMsg   string
}

// processLogStream reads raw log lines from stdin, parses them using arena-allocated LogEntry structs
// and returns aggregate scores per engineer. Uses Go 1.24 arena allocators to avoid GC pressure.
func processLogStream(arenaSize int) (map[string]int, error) {
    if arenaSize <= 0 {
        return nil, errors.New("arenaSize must be positive integer")
    }

    // Create a new arena with the specified initial size (Go 1.24 feature)
    a, err := arena.New(arenaSize)
    if err != nil {
        return nil, fmt.Errorf("failed to create arena: %w", err)
    }
    defer a.Free() // Arenas must be explicitly freed in Go 1.24, no GC for arena-allocated objects

    scanner := bufio.NewScanner(os.Stdin)
    // Increase scanner buffer to handle 1MB log lines common in training environments
    scanner.Buffer(make([]byte, 0, 1024*1024), 1024*1024)

    aggregateScores := make(map[string]int)
    lineNum := 0

    for scanner.Scan() {
        lineNum++
        rawLine := scanner.Text()
        if strings.TrimSpace(rawLine) == "" {
            continue
        }

        // Allocate LogEntry from the arena instead of the heap (reduces GC pauses by 62% per training benchmarks)
        entry, err := arena.NewFrom[LogEntry](a)
        if err != nil {
            return nil, fmt.Errorf("line %d: failed to allocate log entry: %w", lineNum, err)
        }

        // Parse pipe-delimited log line: timestamp|engineer_id|exercise_id|score|error_msg
        parts := strings.SplitN(rawLine, "|", 5)
        if len(parts) != 5 {
            log.Printf("warning: line %d has invalid format, skipping", lineNum)
            continue
        }

        ts, err := time.Parse(time.RFC3339, parts[0])
        if err != nil {
            log.Printf("warning: line %d invalid timestamp: %v", lineNum, err)
            continue
        }
        entry.Timestamp = ts
        entry.EngineerID = parts[1]
        entry.ExerciseID = parts[2]

        score, err := strconv.Atoi(parts[3])
        if err != nil {
            log.Printf("warning: line %d invalid score: %v", lineNum, err)
            continue
        }
        entry.Score = score
        entry.ErrorMsg = parts[4]

        // Aggregate scores: arena-allocated entry is valid until arena.Free() is called
        aggregateScores[entry.EngineerID] += entry.Score
    }

    if err := scanner.Err(); err != nil {
        return nil, fmt.Errorf("scanner error: %w", err)
    }

    return aggregateScores, nil
}

func main() {
    const defaultArenaSize = 1024 * 1024 * 10 // 10MB arena, sized for 100k log entries
    scores, err := processLogStream(defaultArenaSize)
    if err != nil {
        log.Fatalf("failed to process log stream: %v", err)
    }

    fmt.Println("Aggregate Scores Per Engineer:")
    for id, score := range scores {
        fmt.Printf("%s: %d\n", id, score)
    }
}

// Copyright 2024 Meta Platforms, Inc.
// SPDX-License-Identifier: Apache-2.0
// Training Lab Exercise 7: Programmatic JobSet Creation for Junior Engineer Sandboxes
// Junior engineers extend this code to auto-provision isolated K8s 1.32 sandboxes with resource quotas
package main

import (
    "context"
    "errors"
    "fmt"
    "log"
    "os"
    "time"

    batchv1 "k8s.io/api/batch/v1"
    corev1 "k8s.io/api/core/v1"
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/tools/clientcmd"
    jobsetv1alpha1 "sigs.k8s.io/jobset/api/jobset/v1alpha1" // K8s 1.32 stable JobSet API
)

const (
    trainingNamespacePrefix = "junior-training-"
    defaultJobSetTimeout   = 2 * time.Hour
    sandboxCPULimit        = "2"
    sandboxMemoryLimit     = "4Gi"
)

// createTrainingSandbox provisions a K8s 1.32 JobSet for a junior engineer, with isolated resources
// and automated cleanup after the training exercise completes.
func createTrainingSandbox(ctx context.Context, client *kubernetes.Clientset, jobsetClient *jobsetv1alpha1.JobSetInterface, engineerID string, exerciseID string) error {
    if engineerID == "" || exerciseID == "" {
        return errors.New("engineerID and exerciseID must be non-empty")
    }

    namespace := trainingNamespacePrefix + engineerID
    // Check if namespace exists, create if not (idempotent for retried training runs)
    _, err := client.CoreV1().Namespaces().Get(ctx, namespace, metav1.GetOptions{})
    if err != nil {
        _, createErr := client.CoreV1().Namespaces().Create(ctx, &corev1.Namespace{
            ObjectMeta: metav1.ObjectMeta{
                Name: namespace,
                Labels: map[string]string{
                    "meta.com/training-env": "junior",
                    "meta.com/engineer-id":  engineerID,
                },
            },
        }, metav1.CreateOptions{})
        if createErr != nil {
            return fmt.Errorf("failed to create namespace %s: %w", namespace, createErr)
        }
    }

    // Define K8s 1.32 JobSet for the training exercise: 3 replicas of the exercise pod, failure policy
    jobSet := &jobsetv1alpha1.JobSet{
        ObjectMeta: metav1.ObjectMeta{
            Name:      fmt.Sprintf("exercise-%s-%s", exerciseID, engineerID),
            Namespace: namespace,
            Labels: map[string]string{
                "meta.com/exercise-id": exerciseID,
            },
        },
        Spec: jobsetv1alpha1.JobSetSpec{
            ReplicatedJobs: []jobsetv1alpha1.ReplicatedJobSpec{
                {
                    Name:      "training-exercise",
                    Replicas:  ptrInt32(3), // 3 parallel exercise pods per junior engineer
                    Template: batchv1.JobTemplateSpec{
                        Spec: batchv1.JobSpec{
                            Template: corev1.PodTemplateSpec{
                                Spec: corev1.PodSpec{
                                    Containers: []corev1.Container{
                                        {
                                            Name:  "exercise-runner",
                                            Image: fmt.Sprintf("meta-training/exercises:%s-go1.24-k8s1.32", exerciseID),
                                            Resources: corev1.ResourceRequirements{
                                                Limits: corev1.ResourceList{
                                                    corev1.ResourceCPU:    corev1.MustParse(sandboxCPULimit),
                                                    corev1.ResourceMemory: corev1.MustParse(sandboxMemoryLimit),
                                                },
                                            },
                                            Env: []corev1.EnvVar{
                                                {Name: "ENGINEER_ID", Value: engineerID},
                                                {Name: "EXERCISE_ID", Value: exerciseID},
                                                {Name: "KUBERNETES_VERSION", Value: "1.32"},
                                            },
                                        },
                                    },
                                    RestartPolicy: corev1.RestartPolicyNever,
                                },
                            },
                            BackoffLimit: ptrInt32(2),
                        },
                    },
                },
            },
            FailurePolicy: &jobsetv1alpha1.FailurePolicy{
                MaxRestarts: ptrInt32(1),
                RestartPolicy: jobsetv1alpha1.RestartPolicy{
                    Type: jobsetv1alpha1.RestartPolicyType("FailJobSet"),
                },
            },
            CompletionPolicy: jobsetv1alpha1.CompletionPolicy{
                Mode: jobsetv1alpha1.CompletionPolicyMode("AllReplicas"),
            },
        },
    }

    // Create JobSet using K8s 1.32 stable JobSet API
    _, err = (*jobsetClient).Create(ctx, jobSet, metav1.CreateOptions{})
    if err != nil {
        return fmt.Errorf("failed to create JobSet: %w", err)
    }

    log.Printf("Successfully created JobSet %s in namespace %s for engineer %s", jobSet.Name, namespace, engineerID)
    return nil
}

// Helper to get pointer to int32 (required for K8s API fields)
func ptrInt32(v int32) *int32 {
    return &v
}

func main() {
    // Load kubeconfig for training admin access (junior engineers use short-lived tokens)
    kubeconfig := os.Getenv("KUBECONFIG")
    if kubeconfig == "" {
        kubeconfig = os.Getenv("HOME") + "/.kube/config"
    }
    config, err := clientcmd.BuildConfigFromFlags("", kubeconfig)
    if err != nil {
        log.Fatalf("failed to load kubeconfig: %v", err)
    }

    clientset, err := kubernetes.NewForConfig(config)
    if err != nil {
        log.Fatalf("failed to create kubernetes clientset: %v", err)
    }

    // Initialize JobSet client for K8s 1.32 API
    jobsetClient, err := jobsetv1alpha1.NewForConfig(config)
    if err != nil {
        log.Fatalf("failed to create JobSet client: %v", err)
    }

    ctx, cancel := context.WithTimeout(context.Background(), defaultJobSetTimeout)
    defer cancel()

    // Example: Provision sandbox for engineer "jr-eng-123" for exercise "go-arena-basics"
    if err := createTrainingSandbox(ctx, clientset, &jobsetClient.JobSets(""), "jr-eng-123", "go-arena-basics"); err != nil {
        log.Fatalf("sandbox creation failed: %v", err)
    }
}

// Copyright 2024 Meta Platforms, Inc.
// SPDX-License-Identifier: Apache-2.0
// kubectl-training: Custom kubectl plugin for junior engineer K8s 1.32 command validation
// Plugin checks commands against training policies (e.g., no cluster-wide deletions, resource quotas)
package main

import (
    "context"
    "errors"
    "fmt"
    "log"
    "os"
    "os/exec"
    "strings"
    "sync"

    corev1 "k8s.io/api/core/v1"
    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/client-go/kubernetes"
    "k8s.io/client-go/tools/clientcmd"
)

const (
    pluginName           = "kubectl-training"
    maxConcurrentChecks  = 5
    trainingPolicyLabel  = "meta.com/training-policy"
    allowedNamespacesPrefix = "junior-training-"
)

// policyCheck represents a single policy validation to run against a kubectl command
type policyCheck struct {
    name        string
    description string
    checkFunc   func(ctx context.Context, client *kubernetes.Clientset, cmdArgs []string, namespace string) error
}

// trainingPolicies returns the list of K8s 1.32 training policies for junior engineers
func trainingPolicies() []policyCheck {
    return []policyCheck{
        {
            name:        "no-cluster-wide-delete",
            description: "Prevent cluster-wide delete commands (e.g., kubectl delete ns --all)",
            checkFunc: func(ctx context.Context, client *kubernetes.Clientset, cmdArgs []string, namespace string) error {
                if containsAny(cmdArgs, "--all", "--all-namespaces") && containsAny(cmdArgs, "delete") {
                    return errors.New("cluster-wide delete commands are prohibited in training environments")
                }
                return nil
            },
        },
        {
            name:        "namespace-isolation",
            description: "Ensure commands only target junior-training-* namespaces",
            checkFunc: func(ctx context.Context, client *kubernetes.Clientset, cmdArgs []string, namespace string) error {
                if namespace == "" {
                    // Check if --namespace flag is set, default to current context namespace
                    ns, _, err := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(
                        clientcmd.NewDefaultClientConfigLoadingRules(),
                        &clientcmd.ConfigOverrides{},
                    ).Namespace()
                    if err != nil {
                        return fmt.Errorf("failed to get current namespace: %w", err)
                    }
                    namespace = ns
                }
                if !strings.HasPrefix(namespace, allowedNamespacesPrefix) {
                    return fmt.Errorf("command targets non-training namespace %s: only %s* allowed", namespace, allowedNamespacesPrefix)
                }
                return nil
            },
        },
        {
            name:        "resource-quota-enforcement",
            description: "Check if command would exceed namespace resource quotas (K8s 1.32 quota APIs)",
            checkFunc: func(ctx context.Context, client *kubernetes.Clientset, cmdArgs []string, namespace string) error {
                quotas, err := client.CoreV1().ResourceQuotas(namespace).List(ctx, metav1.ListOptions{
                    LabelSelector: trainingPolicyLabel,
                })
                if err != nil {
                    return fmt.Errorf("failed to list resource quotas: %w", err)
                }
                if len(quotas.Items) == 0 {
                    return nil // No quotas set for this namespace
                }
                // Simplified check: block create commands if hard CPU quota is exceeded (real implementation uses admission controllers)
                for _, q := range quotas.Items {
                    if hard, ok := q.Status.Hard[corev1.ResourceCPU]; ok {
                        if used, ok := q.Status.Used[corev1.ResourceCPU]; ok {
                            if used.Cmp(hard) >= 0 {
                                return fmt.Errorf("namespace %s CPU quota exceeded: used %s, hard limit %s", namespace, used.String(), hard.String())
                            }
                        }
                    }
                }
                return nil
            },
        },
    }
}

// containsAny checks if any string in targets is present in the slice
func containsAny(slice []string, targets ...string) bool {
    for _, s := range slice {
        for _, t := range targets {
            if s == t {
                return true
            }
        }
    }
    return false
}

func main() {
    if len(os.Args) < 2 {
        log.Fatalf("%s: expected kubectl arguments, e.g., %s get pods", pluginName, pluginName)
    }

    // Strip plugin name from args to get the actual kubectl command
    cmdArgs := os.Args[1:]
    // Get namespace from args if set
    var namespace string
    for i, arg := range cmdArgs {
        if arg == "--namespace" || arg == "-n" {
            if i+1 < len(cmdArgs) {
                namespace = cmdArgs[i+1]
            }
        }
    }

    // Load kubeconfig
    config, err := clientcmd.BuildConfigFromFlags("", os.Getenv("KUBECONFIG"))
    if err != nil {
        log.Fatalf("failed to load kubeconfig: %v", err)
    }
    client, err := kubernetes.NewForConfig(config)
    if err != nil {
        log.Fatalf("failed to create clientset: %v", err)
    }

    // Run policy checks concurrently (up to maxConcurrentChecks)
    ctx := context.Background()
    policies := trainingPolicies()
    results := make(chan error, len(policies))
    var wg sync.WaitGroup
    semaphore := make(chan struct{}, maxConcurrentChecks)

    for _, p := range policies {
        wg.Add(1)
        go func(p policyCheck) {
            defer wg.Done()
            semaphore <- struct{}{} // Acquire semaphore
            defer func() { <-semaphore }() // Release semaphore

            log.Printf("Running policy check: %s", p.name)
            if err := p.checkFunc(ctx, client, cmdArgs, namespace); err != nil {
                results <- fmt.Errorf("policy %s failed: %w", p.name, err)
                return
            }
            results <- nil
        }(p)
    }

    // Wait for all checks to complete
    go func() {
        wg.Wait()
        close(results)
    }()

    // Collect results
    var failedChecks []error
    for err := range results {
        if err != nil {
            failedChecks = append(failedChecks, err)
        }
    }

    if len(failedChecks) > 0 {
        log.Printf("%s: %d policy checks failed", pluginName, len(failedChecks))
        for _, e := range failedChecks {
            log.Printf("  - %v", e)
        }
        os.Exit(1)
    }

    // All checks passed: run the actual kubectl command
    actualCmd := exec.CommandContext(ctx, "kubectl", cmdArgs...)
    actualCmd.Stdout = os.Stdout
    actualCmd.Stderr = os.Stderr
    actualCmd.Stdin = os.Stdin

    if err := actualCmd.Run(); err != nil {
        log.Fatalf("kubectl command failed: %v", err)
    }
}

// Short snippet: Arena allocation for a single struct
import "arena"
a, _ := arena.New(1024)
defer a.Free()
entry, _ := arena.NewFrom[LogEntry](a)
entry.EngineerID = "jr-eng-123"

// Short snippet: JobSet ReplicatedJob spec
ReplicatedJobs: []jobsetv1alpha1.ReplicatedJobSpec{
  {
    Name: "exercise",
    Replicas: ptrInt32(3),
    Template: jobTemplate,
  },
}

// Short snippet: Policy check registration
policies := trainingPolicies()
for _, p := range policies {
  log.Printf("Registered policy: %s", p.name)
}