Server-side Integration

How server-side integration works

In a client-side architecture the path is: server → HTML with no recommendations → browser → JS
snippet → personalization API → recommendations rendered. That is two sequential round trips, and
the visitor sees the flicker of an empty block filling in.

In a server-side architecture:

1. Browser request → the store's server
2. Server → the personalization API (in parallel with other data)
3. Server receives recommendations and renders them into the template
4. Finished HTML page → browser

The visitor sees recommendations on load, with no delay and no shift.

Architectural patterns

A synchronous call

# Pseudocode: a synchronous call while rendering the page
def render_pdp(product_id, user_id):
    product = db.get_product(product_id)

    try:
        recommendations = personalization_api.get_recommendations(
            user_id=user_id,
            context={"product_id": product_id},
            timeout=200  # ms — a hard timeout
        )
    except TimeoutError:
        recommendations = bestsellers_cache.get()  # fallback

    return render_template("pdp.html",
                           product=product,
                           recommendations=recommendations)

Parallel calls

For pages with several recommendation blocks, the API calls run in parallel:

with ThreadPoolExecutor() as executor:
    future_similar = executor.submit(api.similar_items, product_id)
    future_bought_together = executor.submit(api.bought_together, product_id)

similar = future_similar.result(timeout=0.2)
bought_together = future_bought_together.result(timeout=0.2)

Caching responses

Server-level caching reduces load on the API and removes the risk of degradation at peak traffic.

When to choose server-side

• SEO matters — the recommendation blocks need to be indexable
• A headless or API-first architecture — there is no single JS context
• High traffic — predictable performance is needed, independent of browser speed
• No layout shift — which matters for Core Web Vitals and for the experience

Tip: a hybrid is often the sensible first step: critical blocks — the homepage carousel,
product page recommendations — server-side, and secondary ones such as popups and banners
client-side. It reduces the development scope of a first integration.