Website slow at busy times? Staying fast under peak traffic

Key takeaways

A website that slows down at busy times fails on the days that matter most: the sale, the TV mention, the email to your whole list. Normal speed tests will not show it, because they send one visitor at a time. Sites buckle under load when every visit makes the server build the page from scratch. Caching, a content delivery network and a lighter campaign page prevent most of it.

• 99.9% uptime still allows about 8 hours 46 minutes of downtime a year.
• Speed tests send one visitor. A campaign can send hundreds at once.
• Cached pages let a modest server handle a large crowd.
• Prepare before the campaign: the day itself is too late.

Why does a website slow down when it gets busy?

A website slows under load because the server has a limit on how much work it can do at once. On many sites, each visit asks the server to run code, query a database and assemble a page. Ten visitors a minute is easy. Three hundred in the minute after an email goes out forms a queue, and every visitor waits longer.

Shared hosting adds a second limit. Your site shares a machine with many others, and the host will restrict or suspend a site that uses too much.

• How website speed affects customer experience and conversions
• Website hosting for UK small businesses

What does slowness at peak cost?

It costs the return on whatever caused the peak. You paid for the advert, the email platform or the PR. If the landing page takes ten seconds or shows an error, that spend bought frustration at the moment the most people were watching.

Uptime figures can mislead here. A host promising 99.9% availability is allowing about 8 hours 46 minutes of downtime a year, and 99.5% allows nearly 44 hours. Nothing says those hours will fall at a quiet time.

• What a slow website really costs a UK business

How do you prepare a site for a traffic spike?

Reduce the work each visit needs, and move as much of it as possible away from your server.

• 1. Turn on full-page caching so the server sends a stored copy.
• 2. Put a content delivery network in front to serve files from nearby locations.
• 3. Send campaign traffic to a light page, not the homepage.
• 4. Remove sliders, video and non-essential scripts from that page.
• 5. Ask your host what the plan's limits are and what happens when they are hit.
• 6. Stagger large email sends over an hour or two.

• Website caching explained for business owners
• Do you need a CDN for a small business website?

Which pages cannot simply be cached?

Pages that differ for each visitor cannot be served from a single stored copy. Baskets, checkouts, account pages, live stock levels and search results all need the server. These are the pages that fail first in a sale.

Protect them by keeping everything else off the server, simplifying the checkout and, for shops expecting a real surge, upgrading the plan temporarily. Hosted platforms such as Shopify handle this for you, which is one of the things the subscription pays for.

• Checkout speed: how slow payment steps lose orders

When is this not worth worrying about?

It is not worth much effort if your traffic is steady and your site is mostly informational. A local firm receiving 2,000 visits a month spread across working hours will not overload a decent host. Basic caching is still worth having, because it makes every visit faster, but load testing and standby capacity are for businesses that create their own peaks.

What does this look like in practice?

A pattern we see around promotions: the offer goes to the whole mailing list at nine in the morning, linking to the homepage. The site was fast in testing. Within minutes it slows to a crawl, and the business spends the morning apologising.

Pointing the email at a cached, single-purpose page and sending in batches spreads the load and keeps the offer visible. Global Bridge Labs (GBL) asks about campaign dates before recommending hosting for this reason.

• See client work
• Website Design & Development for UK businesses

Peak traffic checklist

• List the dates when you will send traffic in bulk.
• Confirm full-page caching is on and working.
• Check your hosting plan's limits and overage behaviour.
• Build a light landing page for each campaign.
• Place a test order during a busy hour.
• Set up uptime alerts to a phone, not only email.

• Website speed monitoring: catch slowdowns before customers

Next step

The time to find your site's limit is before the campaign, not during it. Tell us what you are planning and we will check the site can carry it.