Disruption budgets and rolling availability

{
  "sdk": {
    "version": "10.0.403",
    "rollForward": "latestPatch"
  }
}

<Project Sdk="Microsoft.NET.Sdk.Web"><PropertyGroup><TargetFramework>net10.0</TargetFramework><Nullable>enable</Nullable><ImplicitUsings>enable</ImplicitUsings></PropertyGroup><ItemGroup><PackageReference Include="Microsoft.Data.Sqlite" Version="10.0.14" /></ItemGroup></Project>

using Microsoft.AspNetCore.Hosting.Server;
using Microsoft.AspNetCore.Hosting.Server.Features;
using Microsoft.Data.Sqlite;
var builder = WebApplication.CreateBuilder(args);
var settings = new LabSettings {
    Replica = builder.Configuration["Lab:Replica"] ?? "one",
    Workers = builder.Configuration.GetValue("Lab:Workers", 2),
    Partition = builder.Configuration.GetValue("Lab:Partition", 0),
    QueueCapacity = builder.Configuration.GetValue("Lab:QueueCapacity", 4),
    PoolSize = builder.Configuration.GetValue("Lab:PoolSize", 2),
    WorkMilliseconds = builder.Configuration.GetValue("Lab:WorkMilliseconds", 20),
    LedgerPath = builder.Configuration["Lab:LedgerPath"] ?? Path.Combine(Path.GetTempPath(), "sharprune-local-ledger.db")
};
settings.Validate(); builder.Services.AddSingleton(settings); builder.Services.AddSingleton<LabRuntime>(); builder.Services.AddSingleton<LocalIo>();
builder.Services.AddSingleton<IHostedService>(services => services.GetRequiredService<LabRuntime>());
builder.Services.AddSingleton<LocalLedger>(); var app = builder.Build();
app.Services.GetRequiredService<LocalLedger>().Initialize();
app.MapGet("/instance", (LabRuntime lab) => new { replica = settings.Replica, visits = lab.Visit() });
app.MapGet("/live", () => TypedResults.Text("live"));
app.MapGet("/io-delay", async (CancellationToken token) => { await Task.Delay(20, token); return TypedResults.Text("controlled loopback reply"); });
app.MapGet("/io", async (CancellationToken token, IServer server, LocalIo io) => {
    using var response = await io.Client.GetAsync(LocalAddress(server), token); response.EnsureSuccessStatusCode(); _ = await response.Content.ReadAsByteArrayAsync(token);
    return TypedResults.Ok(new { replica = settings.Replica, kind = "async-loopback-http" });
});
app.MapGet("/sync", (CancellationToken token, IServer server, LocalIo io) => {
    using var response = io.Client.GetAsync(LocalAddress(server), token).GetAwaiter().GetResult(); response.EnsureSuccessStatusCode(); _ = response.Content.ReadAsByteArrayAsync(token).GetAwaiter().GetResult();
    return TypedResults.Ok(new { replica = settings.Replica, kind = "deliberate-blocking-demo" });
});
app.MapGet("/cpu", () => { uint value = 1; for (int i = 0; i < 200000; i++) value = unchecked(value * 1664525 + 1013904223); return TypedResults.Ok(new { replica = settings.Replica, kind = "bounded-cpu", value }); });
app.MapGet("/threadpool", () => new { threads = ThreadPool.ThreadCount, pending = ThreadPool.PendingWorkItemCount, completed = ThreadPool.CompletedWorkItemCount });
app.MapGet("/ready", (LabRuntime lab) => lab.Accepting ? Results.Ok(new { ready = true }) : Results.StatusCode(503));
app.MapGet("/stats", (LabRuntime lab) => new { replica = settings.Replica, accepting = lab.Accepting, main = lab.Main.Snapshot(), batch = lab.Batch.Snapshot(), dependencyCalls = lab.Circuit.DependencyCalls });
app.MapGet("/work", (HttpContext context, LabRuntime lab, int? budgetMs) => Handle(context, lab.Main, lab, budgetMs));
app.MapGet("/batch", (HttpContext context, LabRuntime lab, int? budgetMs) => Handle(context, lab.Batch, lab, budgetMs));
app.MapGet("/unstable", (LabRuntime lab, string? key) => {
    if (key != "demo" && key != "always") return Results.BadRequest();
    int attempt = lab.Attempt(key); return key == "always" || attempt == 1 ? Results.StatusCode(503) : Results.Ok(new { replica = settings.Replica, attempt });
});
app.MapGet("/session/{name}", (LabRuntime lab, string name) => name == "demo" ? Results.Ok(new { replica = settings.Replica, value = lab.Session() }) : Results.BadRequest());
app.MapPost("/once/{key}", (string key, LedgerInput input, LocalLedger ledger) => {
    if (key != "demo" || input.Amount is < 1 or > 100) return Results.BadRequest();
    LedgerDecision result = ledger.Record(key, input.Amount); return result.Conflict ? Results.Conflict(new { error = "key amount conflict" }) : Results.Ok(result);
});
app.MapGet("/ledger", (LocalLedger ledger) => new { receipts = ledger.Count() });
app.MapGet("/guarded", (LabRuntime lab) => lab.Circuit.Invoke(lab.DependencyFailing));
app.MapGet("/partition/{key}", (string key, int? owner) => {
    if (key != "A" && key != "B") return Results.BadRequest();
    int partition = StablePartition.For(key, 2);
    return owner == partition && settings.Partition == partition ? Results.Ok(new { replica = settings.Replica, partition, key }) : Results.Conflict(new { expectedPartition = partition });
});
if (app.Environment.IsDevelopment()) {
    app.MapPost("/lab/gate/{lane}/{action}", (string lane, string action, LabRuntime lab) => {
        WorkLane? target = lane == "main" ? lab.Main : lane == "batch" ? lab.Batch : null;
        if (target is null || action != "open" && action != "close") return Results.BadRequest();
        if (action == "open") target.Gate.Open(); else target.Gate.Close(); return Results.NoContent();
    });
    app.MapPost("/lab/drain", (LabRuntime lab) => { lab.Drain(); return Results.NoContent(); });
    app.MapPost("/lab/dependency/{failing:bool}", (bool failing, LabRuntime lab) => { lab.DependencyFailing = failing; return Results.NoContent(); });
}
app.Run();
static async Task<IResult> Handle(HttpContext context, WorkLane lane, LabRuntime lab, int? budgetMs) {
    if (budgetMs is < 1 or > 1000) return Results.BadRequest();
    using var budget = CancellationTokenSource.CreateLinkedTokenSource(context.RequestAborted);
    if (budgetMs is int milliseconds) budget.CancelAfter(milliseconds);
    var item = new WorkItem(budget.Token);
    AdmissionDecision decision = lab.Admit(lane, item);
    if (decision == AdmissionDecision.Draining) return Results.StatusCode(503);
    if (decision == AdmissionDecision.Full) return Results.StatusCode(429);
    try { await item.Completion.Task.WaitAsync(budget.Token); return Results.Ok(new { replica = lab.Settings.Replica, completed = true }); }
    catch (OperationCanceledException) when (!context.RequestAborted.IsCancellationRequested) { return Results.Problem(statusCode: 504, title: "Classroom work budget expired"); }
}
static Uri LocalAddress(IServer server) {
    string address = server.Features.Get<IServerAddressesFeature>()!.Addresses.Single();
    return new UriBuilder("http", "127.0.0.1", new Uri(address).Port) { Path = "/io-delay" }.Uri;
}
public sealed class LocalIo : IDisposable { public HttpClient Client { get; } = new() { Timeout = TimeSpan.FromSeconds(5) }; public void Dispose() => Client.Dispose(); }
public sealed record LedgerInput(int Amount);
public sealed class LabSettings {
    public string Replica { get; init; } = "one"; public int Partition { get; init; } public int Workers { get; init; } public int QueueCapacity { get; init; }
    public int PoolSize { get; init; } public int WorkMilliseconds { get; init; } public string LedgerPath { get; init; } = "";
    public void Validate() {
        if (Partition is < 0 or > 1 || Replica.Length is < 1 or > 32 || Workers is < 1 or > 8 || QueueCapacity is < 1 or > 16 || PoolSize is < 1 or > 8 || WorkMilliseconds is < 1 or > 250 || string.IsNullOrWhiteSpace(LedgerPath)) throw new InvalidOperationException("Invalid bounded lab settings");
    }
}
public enum AdmissionDecision { Accepted, Full, Draining }
public sealed class LabRuntime : IHostedService, IDisposable {
    private readonly object admissionSync = new();
    private int accepting = 1, visits, sessions, demoAttempts, alwaysAttempts, failing = 1, disposed;
    public LabSettings Settings { get; } public WorkLane Main { get; } public WorkLane Batch { get; }
    public ClassroomCircuit Circuit { get; } = new();
    public LabRuntime(LabSettings settings) { Settings = settings; Main = new(settings.Workers, settings.QueueCapacity, settings.PoolSize, settings.WorkMilliseconds); Batch = new(1, 1, 1, settings.WorkMilliseconds); }
    public bool Accepting => Volatile.Read(ref accepting) == 1;
    public bool DependencyFailing { get => Volatile.Read(ref failing) == 1; set => Volatile.Write(ref failing, value ? 1 : 0); }
    public void Drain() { lock (admissionSync) Volatile.Write(ref accepting, 0); }
    public AdmissionDecision Admit(WorkLane lane, WorkItem item) {
        lock (admissionSync) {
            if (!Accepting) return AdmissionDecision.Draining;
            return lane.TrySubmit(item) ? AdmissionDecision.Accepted : AdmissionDecision.Full;
        }
    }
    public int Visit() => Interlocked.Increment(ref visits); public int Session() => Interlocked.Increment(ref sessions);
    public int Attempt(string key) => key == "demo" ? Interlocked.Increment(ref demoAttempts) : Interlocked.Increment(ref alwaysAttempts);
    public Task StartAsync(CancellationToken token) { Main.Start(); Batch.Start(); return Task.CompletedTask; }
    public Task StopAsync(CancellationToken token) => Task.WhenAll(Main.StopAsync(token), Batch.StopAsync(token));
    public void Dispose() { if (Interlocked.Exchange(ref disposed, 1) != 0) return; Main.Dispose(); Batch.Dispose(); }
}
public static class StablePartition {
    public static int For(string key, int count) { uint hash = 2166136261; foreach (byte b in System.Text.Encoding.UTF8.GetBytes(key)) hash = unchecked((hash ^ b) * 16777619); return (int)(hash % (uint)count); }
}

using System.Threading.Channels;
public sealed record WorkItem(CancellationToken Token) { public TaskCompletionSource<bool> Completion { get; } = new(TaskCreationOptions.RunContinuationsAsynchronously); }
public sealed class AsyncGate {
    private readonly object sync = new(); private TaskCompletionSource<bool> source = Completed();
    private static TaskCompletionSource<bool> Completed() { var value = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously); value.SetResult(true); return value; }
    public void Close() { lock (sync) { if (source.Task.IsCompleted) source = new(TaskCreationOptions.RunContinuationsAsynchronously); } }
    public void Open() { lock (sync) source.TrySetResult(true); }
    public Task WaitAsync(CancellationToken token) { lock (sync) return source.Task.WaitAsync(token); }
}
public sealed class WorkLane : IDisposable {
    private readonly Channel<WorkItem> queue; private readonly SemaphoreSlim pool; private readonly int workers, milliseconds;
    private readonly CancellationTokenSource stop = new(); private Task[] running = Array.Empty<Task>();
    private int active, inPool, maxActive, maxPool, accepted, rejected, completed, canceled, disposed;
    public AsyncGate Gate { get; } = new();
    public WorkLane(int workers, int capacity, int poolSize, int milliseconds) {
        this.workers = workers; this.milliseconds = milliseconds; pool = new(poolSize, poolSize);
        queue = Channel.CreateBounded<WorkItem>(new BoundedChannelOptions(capacity) { FullMode = BoundedChannelFullMode.Wait, SingleWriter = false, SingleReader = workers == 1 });
    }
    public void Start() { running = Enumerable.Range(0, workers).Select(_ => RunAsync()).ToArray(); }
    public bool TrySubmit(WorkItem item) { if (queue.Writer.TryWrite(item)) { Interlocked.Increment(ref accepted); return true; } Interlocked.Increment(ref rejected); return false; }
    private async Task RunAsync() {
        await foreach (WorkItem item in queue.Reader.ReadAllAsync(stop.Token)) {
            int now = Interlocked.Increment(ref active); Maximum(ref maxActive, now); bool entered = false;
            using var lifetime = CancellationTokenSource.CreateLinkedTokenSource(item.Token, stop.Token);
            try {
                lifetime.Token.ThrowIfCancellationRequested(); await Gate.WaitAsync(lifetime.Token);
                await pool.WaitAsync(lifetime.Token); entered = true; Maximum(ref maxPool, Interlocked.Increment(ref inPool));
                await Task.Delay(milliseconds, lifetime.Token); Interlocked.Increment(ref completed); item.Completion.TrySetResult(true);
            } catch (OperationCanceledException) { Interlocked.Increment(ref canceled); item.Completion.TrySetCanceled(lifetime.Token); }
            finally { if (entered) { Interlocked.Decrement(ref inPool); pool.Release(); } Interlocked.Decrement(ref active); }
        }
    }
    private static void Maximum(ref int field, int value) { int old; do { old = Volatile.Read(ref field); if (old >= value) return; } while (Interlocked.CompareExchange(ref field, value, old) != old); }
    public object Snapshot() => new { active = Volatile.Read(ref active), queued = queue.Reader.Count, inPool = Volatile.Read(ref inPool), maxActive = Volatile.Read(ref maxActive), maxPool = Volatile.Read(ref maxPool), accepted = Volatile.Read(ref accepted), rejected = Volatile.Read(ref rejected), completed = Volatile.Read(ref completed), canceled = Volatile.Read(ref canceled) };
    public async Task StopAsync(CancellationToken token) {
        queue.Writer.TryComplete();
        try { await Task.WhenAll(running).WaitAsync(token); }
        catch (OperationCanceledException) when (token.IsCancellationRequested) { stop.Cancel(); Gate.Open(); try { await Task.WhenAll(running); } catch (OperationCanceledException) { } }
    }
    public void Dispose() { if (Interlocked.Exchange(ref disposed, 1) != 0) return; stop.Cancel(); pool.Dispose(); stop.Dispose(); }
}

using Microsoft.Data.Sqlite;
public sealed record LedgerDecision(bool Replay, bool Conflict, int Amount);
public sealed class LocalLedger {
    private readonly string connectionString;
    public LocalLedger(LabSettings settings) { connectionString = new SqliteConnectionStringBuilder { DataSource = settings.LedgerPath, DefaultTimeout = 2 }.ToString(); }
    private SqliteConnection Open() { var connection = new SqliteConnection(connectionString); connection.Open(); return connection; }
    public void Initialize() { using var connection = Open(); using var command = connection.CreateCommand(); command.CommandText = "CREATE TABLE IF NOT EXISTS receipts (request_key TEXT PRIMARY KEY, amount INTEGER NOT NULL)"; command.ExecuteNonQuery(); }
    public LedgerDecision Record(string key, int amount) {
        using var connection = Open(); using var transaction = connection.BeginTransaction();
        using var insert = connection.CreateCommand(); insert.Transaction = transaction;
        insert.CommandText = "INSERT INTO receipts(request_key, amount) VALUES ($key, $amount) ON CONFLICT(request_key) DO NOTHING";
        insert.Parameters.AddWithValue("$key", key); insert.Parameters.AddWithValue("$amount", amount); int changed = insert.ExecuteNonQuery();
        using var read = connection.CreateCommand(); read.Transaction = transaction; read.CommandText = "SELECT amount FROM receipts WHERE request_key = $key"; read.Parameters.AddWithValue("$key", key);
        int stored = Convert.ToInt32(read.ExecuteScalar(), System.Globalization.CultureInfo.InvariantCulture); transaction.Commit();
        return new LedgerDecision(changed == 0, stored != amount, stored);
    }
    public int Count() { using var connection = Open(); using var read = connection.CreateCommand(); read.CommandText = "SELECT COUNT(*) FROM receipts"; return Convert.ToInt32(read.ExecuteScalar(), System.Globalization.CultureInfo.InvariantCulture); }
}

public sealed class ClassroomCircuit {
    private readonly object sync = new(); private int failures, calls; private bool probe; private DateTimeOffset openUntil = DateTimeOffset.MinValue;
    public int DependencyCalls { get { lock (sync) return calls; } }
    public IResult Invoke(bool failing) {
        lock (sync) {
            DateTimeOffset now = DateTimeOffset.UtcNow;
            if (openUntil != DateTimeOffset.MinValue && now < openUntil) return Results.Json(new { state = "open", called = false }, statusCode: 503);
            if (probe) return Results.Json(new { state = "probe-busy", called = false }, statusCode: 503);
            bool halfOpen = openUntil != DateTimeOffset.MinValue; if (halfOpen) probe = true;
            calls++;
            // The dependency is an explicitly controlled in-process classroom outcome, not a real remote service.
            if (failing) {
                failures++; if (halfOpen || failures >= 2) openUntil = now.AddMilliseconds(250); probe = false;
                return Results.Json(new { state = openUntil == DateTimeOffset.MinValue ? "closed" : "open", called = true }, statusCode: 503);
            }
            failures = 0; openUntil = DateTimeOffset.MinValue; probe = false; return Results.Ok(new { state = "closed", called = true });
        }
    }
}

<Project Sdk="Microsoft.NET.Sdk"><PropertyGroup><OutputType>Exe</OutputType><TargetFramework>net10.0</TargetFramework><Nullable>enable</Nullable><ImplicitUsings>enable</ImplicitUsings></PropertyGroup></Project>

using System.Collections.Concurrent;
using System.Diagnostics;
using System.Globalization;
using System.Text.Json;
if (args.Length < 2) throw new ArgumentException("Usage: closed|open|retry|shard|hot|io|cpu|sync baseUrl[,baseUrl] [count<=32] [concurrency<=8] [intervalMs]");
string mode = args[0];
if (!new[] { "closed", "open", "retry", "shard", "hot", "io", "cpu", "sync" }.Contains(mode)) throw new ArgumentException("Unknown mode");
Uri[] targets = args[1].Split(',').Select(s => new Uri(s.TrimEnd('/') + "/")).ToArray();
if (targets.Length is < 1 or > 2 || targets.Any(u => !u.IsLoopback || u.Scheme != "http" || u.AbsolutePath != "/" || !string.IsNullOrEmpty(u.Query) || !string.IsNullOrEmpty(u.UserInfo))) throw new ArgumentException("Only one or two owned HTTP loopback roots are allowed");
int count = args.Length > 2 ? int.Parse(args[2], CultureInfo.InvariantCulture) : 16;
int concurrency = args.Length > 3 ? int.Parse(args[3], CultureInfo.InvariantCulture) : 4;
int interval = args.Length > 4 ? int.Parse(args[4], CultureInfo.InvariantCulture) : 2;
if (count is < 1 or > 32 || concurrency is < 1 or > 8 || interval is < 1 or > 100 || (mode == "shard" || mode == "hot") && targets.Length != 2) throw new ArgumentException("Bounded local settings required");
using var client = new HttpClient { Timeout = TimeSpan.FromSeconds(5) };
var latencies = new ConcurrentBag<double>(); var replicas = new ConcurrentDictionary<string, byte>(StringComparer.Ordinal);
int attempted = 0, successful = 0, rejected = 0, skipped = 0, logical = 0;
async Task Invoke(int index) {
    string key = mode == "hot" || index % 2 == 0 ? "A" : "B"; int partition = Partition(key);
    Uri target = targets[(mode == "shard" || mode == "hot") ? partition : index % targets.Length];
    string route = mode switch { "retry" => "unstable?key=demo", "shard" or "hot" => "partition/" + key + "?owner=" + partition, "io" => "io", "cpu" => "cpu", "sync" => "sync", _ => "work" };
    int maximumAttempts = mode == "retry" ? 2 : 1;
    for (int attempt = 1; attempt <= maximumAttempts; attempt++) {
        var begin = Stopwatch.GetTimestamp(); Interlocked.Increment(ref attempted);
        using var request = new HttpRequestMessage(HttpMethod.Get, new Uri(target, route));
        using var response = await client.SendAsync(request); string body = await response.Content.ReadAsStringAsync();
        latencies.Add(Stopwatch.GetElapsedTime(begin).TotalMilliseconds);
        if ((int)response.StatusCode == 503 && attempt < maximumAttempts) { await Task.Delay(10 + index % 7); continue; }
        if (response.IsSuccessStatusCode) {
            Interlocked.Increment(ref successful); using var doc = JsonDocument.Parse(body);
            if (doc.RootElement.TryGetProperty("replica", out var name)) replicas.TryAdd(name.GetString()!, 0);
        } else Interlocked.Increment(ref rejected);
        break;
    }
}
var elapsed = Stopwatch.StartNew();
if (mode == "open") {
    using var slots = new SemaphoreSlim(concurrency, concurrency); var running = new List<Task>();
    for (int i = 0; i < count; i++) {
        double wait = i * interval - elapsed.Elapsed.TotalMilliseconds; if (wait > 0) await Task.Delay(TimeSpan.FromMilliseconds(wait));
        Interlocked.Increment(ref logical);
        if (!slots.Wait(0)) { Interlocked.Increment(ref skipped); continue; }
        int index = i; running.Add(Release(index));
    }
    await Task.WhenAll(running);
    async Task Release(int index) { try { await Invoke(index); } finally { slots.Release(); } }
} else {
    int next = -1;
    await Task.WhenAll(Enumerable.Range(0, concurrency).Select(async _ => {
        while (true) { int index = Interlocked.Increment(ref next); if (index >= count) return; Interlocked.Increment(ref logical); await Invoke(index); }
    }));
}
elapsed.Stop(); double[] sorted = latencies.OrderBy(x => x).ToArray();
double Percentile(double probability) => sorted.Length == 0 ? 0 : sorted[(int)Math.Ceiling(probability * sorted.Length) - 1];
Console.WriteLine(JsonSerializer.Serialize(new { mode, scheduled = logical, attempted, successful, rejected, skipped, concurrency, elapsedMs = elapsed.Elapsed.TotalMilliseconds, p50Ms = Percentile(.5), p95Ms = Percentile(.95), p99Ms = Percentile(.99), replicas = replicas.Keys.OrderBy(x => x).ToArray() }));
static int Partition(string key) { uint hash = 2166136261; foreach (byte b in System.Text.Encoding.UTF8.GetBytes(key)) hash = unchecked((hash ^ b) * 16777619); return (int)(hash % 2); }

{
  "Lab": {
    "Replica": "one",
    "Workers": 2,
    "QueueCapacity": 4,
    "PoolSize": 2,
    "WorkMilliseconds": 20
  }
}

FROM mcr.microsoft.com/dotnet/sdk:10.0.403 AS build
WORKDIR /src
COPY global.json ./
COPY Server/ Server/
RUN dotnet restore Server/Lab.Server.csproj --source https://api.nuget.org/v3/index.json
RUN dotnet publish Server/Lab.Server.csproj --no-restore -c Release -o /out
FROM mcr.microsoft.com/dotnet/aspnet:10.0.14
WORKDIR /app
COPY --from=build /out/ ./
ENV ASPNETCORE_URLS=http://+:8080
ENV Lab__LedgerPath=/tmp/classroom-ledger.db
USER $APP_UID
EXPOSE 8080
ENTRYPOINT ["dotnet", "Lab.Server.dll"]

apiVersion: apps/v1
kind: Deployment
metadata:
  name: load-lab
spec:
  replicas: 2
  selector:
    matchLabels: {app: load-lab}
  strategy:
    type: RollingUpdate
    rollingUpdate: {maxUnavailable: 0, maxSurge: 1}
  template:
    metadata:
      labels: {app: load-lab}
    spec:
      terminationGracePeriodSeconds: 30
      containers:
        - name: server
          image: sharprune-load-lab:local
          imagePullPolicy: IfNotPresent
          ports: [{containerPort: 8080}]
          env:
            - name: ASPNETCORE_ENVIRONMENT
              value: Production
            - name: Lab__Replica
              valueFrom:
                fieldRef: {fieldPath: metadata.name}
            - name: Lab__LedgerPath
              value: /tmp/classroom-ledger.db
          resources:
            requests: {cpu: 100m, memory: 64Mi}
            limits: {cpu: 500m, memory: 128Mi}
          startupProbe:
            httpGet: {path: /live, port: 8080}
            periodSeconds: 2
            failureThreshold: 30
          readinessProbe:
            httpGet: {path: /ready, port: 8080}
            periodSeconds: 2
          livenessProbe:
            httpGet: {path: /live, port: 8080}
            periodSeconds: 10
---
apiVersion: v1
kind: Service
metadata:
  name: load-lab
spec:
  selector: {app: load-lab}
  ports: [{port: 8080, targetPort: 8080}]

apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: load-lab
spec:
  minAvailable: 1
  selector:
    matchLabels: {app: load-lab}

# Optional Kubernetes exercise, not executed by the portable console
Use only a cluster/namespace you own and explicitly select. Build the supplied Dockerfile, load its local image into your own local cluster or replace the image reference with your own published digest. The manifests use apps/v1 Deployment, v1 Service, autoscaling/v2 HPA and policy/v1 PDB where supplied. HPA needs a functioning resource metrics API such as Metrics Server and CPU requests on every measured container. These resources do not install Metrics Server.
The normal /work endpoint is an asynchronous delay workload, so CPU utilization need not rise with queueing. This CPU HPA example is not a promise that the delay workload will scale; a queue-based custom metric requires a separate metrics adapter and policy. Do not increase load beyond the driver bounds to force a screenshot.
The SQLite path is per-pod ephemeral /tmp storage. It is NOT a cross-pod shared database, not durable storage and not a production idempotency service. The two-process shared-file lesson is a separate owned desktop experiment. No PVC, distributed database, ingress, TLS or credentials are provisioned.
A PDB constrains qualifying voluntary evictions; it does not prevent node loss or set a Deployment rolling-update budget. That budget is expressed separately in maxUnavailable/maxSurge. Startup/readiness/liveness and graceful termination still require target-environment tests.
Client YAML parsing or client-side dry-run is not proof that a server accepted resources or that autoscaling/eviction behavior executed. Do not apply to an existing public or production cluster as part of this lesson. Record which checks actually ran.