Vertical Scaling (Scale-Up) & Horizontal Scaling (Scale-out)

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Horizontal vs Vertical Scaling — Try It Yourself</title>
<style>
.infographic-scaling {
  --ink:        #1a1a1a;
  --ink-soft:   #5c5c5c;
  --paper:      #ffffff;
  --paper-alt:  #f0ece4;
  --accent:     #2563eb;
  --accent-soft:#e3ebfd;
  --line:       #ddd6c9;
  --good:       #16a34a;
  --good-soft:  #dcfce7;
  --bad:        #dc2626;
  --bad-soft:   #fee2e2;
  --warn:       #b45309;
  --on-accent:  #ffffff;
  --display-font: Georgia, 'Iowan Old Style', serif;
  --body-font: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --mono-font: 'SF Mono', Consolas, monospace;

  background: var(--paper);
  color: var(--ink);
  font-family: var(--body-font);
  max-width: 840px;
  margin: 0 auto;
  box-sizing: border-box;
  overflow-x: hidden;
}
.infographic-scaling[data-theme="dark"] {
  --ink:        #e8e6e1;
  --ink-soft:   #9a968c;
  --paper:      #121212;
  --paper-alt:  #1e1e26;
  --accent:     #5b8def;
  --accent-soft:#202942;
  --line:       #2c313d;
  --good:       #4ade80;
  --good-soft:  #123420;
  --bad:        #f87171;
  --bad-soft:   #3a1414;
  --warn:       #fbbf24;
  --on-accent:  #101418;
}
.infographic-scaling * { box-sizing: border-box; }

.sc-head { text-align: center; margin-bottom: 0.25rem; }
.sc-head h2 { font-family: var(--display-font); font-size: 1.85rem; margin: 0 0 0.5rem; }
.sc-head p { color: var(--ink-soft); font-size: 0.95rem; margin: 0 auto; max-width: 600px; line-height: 1.55; }

.sc-frame { background: var(--paper-alt); border: 1px solid var(--line); border-radius: 10px; padding: 1.25rem; margin-top: 1.5rem; }
.sc-frame-desc { text-align: center; font-size: 0.85rem; color: var(--ink-soft); margin: 0 0 1rem; line-height: 1.5; }

.sc-diagram-scroll { overflow-x: auto; }
.sc-diagram-scroll svg { width: 100%; height: auto; display: block; min-width: 460px; }

.sc-server-body { fill: var(--paper); stroke: var(--accent); stroke-width: 2; transition: x 0.8s ease, y 0.8s ease, width 0.8s ease, height 0.8s ease; }
.sc-server-slot { fill: var(--accent-soft); transition: opacity 0.4s ease; }
.sc-server-label { font-size: 10px; font-family: var(--mono-font); text-anchor: middle; fill: var(--ink-soft); transition: x 0.8s ease, y 0.8s ease; }

.sc-meter-bg { fill: var(--line); transition: x 0.6s ease, y 0.6s ease, width 0.6s ease; }
.sc-meter-fill { transition: width 0.8s ease, fill 0.5s ease, x 0.6s ease, y 0.6s ease; }
.sc-meter-text { font-size: 10px; font-family: var(--mono-font); text-anchor: middle; fill: var(--ink); transition: x 0.6s ease, y 0.6s ease; }

.sc-newserver { opacity: 0; transform: translateY(-14px); transition: opacity 0.5s ease, transform 0.5s ease; }
.sc-newserver.is-in { opacity: 1; transform: translateY(0); }

.sc-run-row { display: flex; justify-content: center; gap: 0.6rem; margin-top: 1.25rem; flex-wrap: wrap; }
.sc-run-btn {
  font: inherit; font-size: 0.85rem; background: var(--accent); color: var(--on-accent);
  border: none; border-radius: 7px; padding: 0.6rem 1.1rem; cursor: pointer;
}
.sc-run-btn:hover { opacity: 0.9; }
.sc-run-btn:disabled { opacity: 0.5; cursor: not-allowed; }
.sc-run-btn.is-secondary { background: var(--paper); color: var(--ink); border: 1px solid var(--line); }

.sc-msg { margin-top: 1rem; padding: 0.65rem 0.9rem; border-radius: 8px; font-size: 0.85rem; line-height: 1.55; display: none; }
.sc-msg.is-visible { display: block; }
.sc-msg.st-good { background: var(--good-soft); color: var(--good); }
.sc-msg.st-bad { background: var(--bad-soft); color: var(--bad); }

@media (prefers-reduced-motion: reduce) {
  .infographic-scaling *, .infographic-scaling *::before, .infographic-scaling *::after {
    transition-duration: 0.001ms !important; animation-duration: 0.001ms !important;
  }
}
</style>
</head>
<body>

<div class="infographic-scaling" id="scaling">

  <div class="sc-head">
    <h2>Horizontal vs Vertical Scaling</h2>
    <p>Traffic just spiked and this server is nearly maxed out. Pick how you'd respond, and watch what actually happens to the load.</p>
  </div>

  <div class="sc-frame">
    <p class="sc-frame-desc">🔴 Server 1 is at 90% load. Choose a scaling strategy.</p>
    <div class="sc-diagram-scroll">
      <svg viewBox="0 0 620 260" id="scSvg"></svg>
    </div>

    <div class="sc-run-row">
      <button class="sc-run-btn" id="horizBtn" type="button">➡️ Scale Horizontally (add a server)</button>
      <button class="sc-run-btn" id="vertBtn" type="button">⬆️ Scale Vertically (upgrade this server)</button>
      <button class="sc-run-btn is-secondary" id="scReset" type="button">↺ Reset</button>
    </div>
    <p class="sc-msg" id="scMsg"></p>
  </div>

</div>

<script>
(function () {
  const wrapper = document.getElementById('scaling');
  const bodyAttr = document.body.getAttribute('data-darkmode');
  let dark;
  if (bodyAttr === 'true') {
    dark = true;
  } else if (bodyAttr === 'false') {
    dark = false;
  } else {
    const match = document.cookie.match(/(?:^|;\s*)darkMode=([^;]+)/);
    dark = match ? match[1] === 'true' : false;
  }
  if (dark) wrapper.setAttribute('data-theme', 'dark');
})();

(function () {
  const svg = document.getElementById('scSvg');
  const horizBtn = document.getElementById('horizBtn');
  const vertBtn = document.getElementById('vertBtn');
  const msg = document.getElementById('scMsg');

  function showMsg(text, kind) {
    msg.textContent = text;
    msg.className = 'sc-msg is-visible st-' + kind;
  }

  function meterColor(pct) {
    if (pct >= 80) return 'var(--bad)';
    if (pct >= 55) return 'var(--warn)';
    return 'var(--good)';
  }

  function ns(tag, attrs) {
    const el = document.createElementNS('http://www.w3.org/2000/svg', tag);
    Object.keys(attrs).forEach(k => el.setAttribute(k, attrs[k]));
    return el;
  }

  // ---- build one server group (box + slots + label + meter), all elements kept around so they can animate ----
  function buildServer(id, x, y, w, h, slots) {
    const g = ns('g', { id: 'g-' + id });
    const box = ns('rect', { id: 'box-' + id, class: 'sc-server-body', x, y, width: w, height: h, rx: 6 });
    g.appendChild(box);
    const slotEls = [];
    for (let i = 0; i < 10; i++) {
      const el = ns('rect', { class: 'sc-server-slot', x: x + 8, y: 0, width: w - 16, height: 0, rx: 2, opacity: i < slots ? 1 : 0 });
      g.appendChild(el);
      slotEls.push(el);
    }
    const label = ns('text', { id: 'label-' + id, class: 'sc-server-label', x: x + w / 2, y: y + h + 20 });
    label.textContent = 'Server ' + id;
    g.appendChild(label);

    const meterY = y + h + 35;
    const meterBg = ns('rect', { id: 'meterbg-' + id, class: 'sc-meter-bg', x: x - 10, y: meterY, width: w + 20, height: 10, rx: 5 });
    const meterFill = ns('rect', { id: 'meterfill-' + id, class: 'sc-meter-fill', x: x - 10, y: meterY, width: 0, height: 10, rx: 5, fill: 'var(--good)' });
    const meterText = ns('text', { id: 'metertext-' + id, class: 'sc-meter-text', x: x - 10 + (w + 20) / 2, y: meterY + 24 });
    meterText.textContent = 'load: 0%';
    g.appendChild(meterBg); g.appendChild(meterFill); g.appendChild(meterText);

    layoutSlots(slotEls, x, y, w, h, slots);
    return { g, box, slotEls, label, meterBg, meterFill, meterText, x, y, w, h, meterY };
  }

  function layoutSlots(slotEls, x, y, w, h, activeCount) {
    const slotH = (h - 16) / 10;
    slotEls.forEach((el, i) => {
      el.setAttribute('x', x + 8);
      el.setAttribute('y', y + 8 + i * slotH);
      el.setAttribute('width', w - 16);
      el.setAttribute('height', Math.max(0, slotH - 4));
      el.setAttribute('opacity', i < activeCount ? 1 : 0);
    });
  }

  function setMeter(id, pct) {
    const s = servers[id];
    const fullW = s.w + 20;
    s.meterFill.setAttribute('width', fullW * pct / 100);
    s.meterFill.setAttribute('fill', meterColor(pct));
    s.meterText.textContent = 'load: ' + pct + '%';
  }

  function moveServer(id, x, y, w, h) {
    const s = servers[id];
    s.box.setAttribute('x', x); s.box.setAttribute('y', y);
    s.box.setAttribute('width', w); s.box.setAttribute('height', h);
    s.label.setAttribute('x', x + w / 2); s.label.setAttribute('y', y + h + 20);
    const meterY = y + h + 35;
    const fullW = w + 20;
    s.meterBg.setAttribute('x', x - 10); s.meterBg.setAttribute('y', meterY); s.meterBg.setAttribute('width', fullW);
    s.meterFill.setAttribute('x', x - 10); s.meterFill.setAttribute('y', meterY);
    s.meterText.setAttribute('x', x - 10 + fullW / 2); s.meterText.setAttribute('y', meterY + 24);
    layoutSlots(s.slotEls, x, y, w, h, s.currentSlots || 6);
    s.x = x; s.y = y; s.w = w; s.h = h; s.meterY = meterY;
  }

  let servers = {};

  function init() {
    svg.innerHTML = '';
    servers = {};
    const s1 = buildServer(1, 260, 30, 100, 130, 6);
    s1.currentSlots = 6;
    servers[1] = s1;
    svg.appendChild(s1.g);
    setMeter(1, 90);
  }
  init();

  horizBtn.addEventListener('click', () => {
    horizBtn.disabled = true;
    vertBtn.disabled = true;

    // 1) Server 1's load smoothly drops to its share (30%)
    setMeter(1, 30);
    showMsg('✔️ Adding servers... the same traffic starts spreading out as each new one comes online.', 'good');

    // 2) Server 2 slides in from above, fades in, then its meter fills up
    setTimeout(() => {
      const s2 = buildServer(2, 260, 30, 100, 130, 6);
      s2.currentSlots = 6;
      s2.g.classList.add('sc-newserver');
      servers[2] = s2;
      svg.appendChild(s2.g);
      requestAnimationFrame(() => {
        moveServer(2, 90, 30, 100, 130);
        s2.g.classList.add('is-in');
      });
      setTimeout(() => setMeter(2, 30), 500);
    }, 500);

    // 3) Server 3 does the same, arriving a beat later
    setTimeout(() => {
      const s3 = buildServer(3, 430, 30, 100, 130, 6);
      s3.currentSlots = 6;
      s3.g.classList.add('sc-newserver');
      servers[3] = s3;
      svg.appendChild(s3.g);
      requestAnimationFrame(() => s3.g.classList.add('is-in'));
      setTimeout(() => setMeter(3, 30), 500);
    }, 1300);

    setTimeout(() => {
      showMsg('✔️ Horizontal scaling: two more servers joined, and the same total traffic now splits across all three — each one sits around 30% instead of one server drowning at 90%. Needs a load balancer in front, but there\u2019s no hard ceiling — keep adding boxes as traffic grows.', 'good');
    }, 2000);
  });

  vertBtn.addEventListener('click', () => {
    horizBtn.disabled = true;
    vertBtn.disabled = true;

    showMsg('✔️ Upgrading Server 1 in place — more CPU, RAM and disk added to the same machine...', 'good');

    // grow the SAME server box wider and taller, centered on its original horizontal center
    moveServer(1, 230, 5, 160, 175);
    servers[1].label.textContent = 'Server 1 (upgraded)';

    // reveal extra internal capacity (slots) as it finishes growing, then drop the load %
    setTimeout(() => {
      servers[1].currentSlots = 9;
      layoutSlots(servers[1].slotEls, servers[1].x, servers[1].y, servers[1].w, servers[1].h, 9);
    }, 500);

    setTimeout(() => {
      setMeter(1, 22);
      showMsg('✔️ Vertical scaling: the same one server got more capacity, so its capacity grew — the same traffic is now a smaller share of a bigger machine (22%). Simpler, no distributed-systems complexity — but there\u2019s a ceiling on how big a single machine can get, and upgrading it often means downtime.', 'good');
    }, 900);
  });

  document.getElementById('scReset').addEventListener('click', () => {
    horizBtn.disabled = false;
    vertBtn.disabled = false;
    msg.classList.remove('is-visible');
    init();
  });
})();
</script>

</body>
</html>

.demo {
  font-family: system-ui, sans-serif;
  padding: 16px;
}

.demo h1 {
  color: #2563eb;
  margin: 0 0 8px;
}

.demo p {
  color: #4b5563;
  margin: 0;
}

document.querySelector('.demo h1')?.addEventListener('click', () => {
  alert('Hello from live preview!');
});