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Ops runbook · Beginner · 10 min

Adding an Addon Domain Without Slowing the First One

You want a second site on the same plan without the first one's TTFB drifting upwards — so the document root, the cache boundary and the resource maths all matter.

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The short answer

Create the addon from cPanel's Domains page and give it a document root beside public_html rather than inside it — then treat the two sites as one resource budget, because that is exactly what the server does.

Each addon is a separate vhost with its own cache namespace, its own AutoSSL certificate and its own mail, but it draws on the same CPU allowance, the same RAM ceiling and the same MySQL count as the site you already run. Sprint carries one site, Turbo twenty-five and Nitro a hundred, so the tier decides how much stacking is sensible before contention shows up in your response times.

By the HostingFast team · Reviewed 12 August 2026

Beginner

Assumed level

5

Steps to done

Free

Support cost

Proven

Verified on production

This takes about ten minutes of clicking and a few days of watching. The clicking is trivial; the watching is the part people skip, which is why the second site so often arrives alongside a quiet regression on the first.

Everything below is done from cPanel and a terminal. SSH with Git and Composer is on every shared tier here, so if you would rather check a document root with ls than with a file manager, nothing stops you.

What a second vhost actually costs

The addon gets its own hostname and its own directory, but not its own hardware. Sprint and Turbo accounts run on one core and 2 GB of RAM; Nitro doubles that to two cores and 4 GB. Two WordPress installs behind a warm LiteSpeed cache barely register, because a cached response never reaches PHP at all. Two uncached WooCommerce checkouts on one core is a different arithmetic entirely.

The other shared quotas are worth checking before you start: 25 MySQL databases on Sprint, 50 on Turbo, 100 on Nitro, and a disk allowance of 10, 20 or 200 GB respectively. An addon domain that will host a real application needs a database slot and disk headroom, not just a DNS record.

Where the document root goes, and why nesting breaks things

Put the root at /domains/example.com, a sibling of public_html. Nest it at public_html/example.com and the second site becomes reachable at two addresses: its own domain, and yourdomain.com/example.com. That is a duplicate-content problem you will be writing canonical tags to fix, and it also means one site's .htaccess sits above the other in the directory chain, so a rewrite rule written for the parent gets applied to the child.

Name the directory after the domain and nothing else. Six months and four addons later, /domains/example.com reads like an index; /domains/site2-new-final does not, and you will be the one guessing which vhost it serves.

Measuring the two sites separately

cPanel's Resource Usage page shows the account's CPU, memory and entry-process figures over time, and it is account-wide — it will tell you that something is saturating the allowance, not which vhost did it. To attribute it, read the raw access log for each domain and count requests by host, then compare cache hit ratios. On Nitro, PHP X-Ray on CloudLinux Pro goes further and names the slow function inside the request.

Take a TTFB baseline for both hostnames before you add traffic, and again a fortnight later: curl -o /dev/null -s -w 'ttfb %{time_starttransfer}\n' https://example.com. Two numbers a fortnight apart is the whole method, and it is the only way to answer the question people ask after the fact — did the second site slow the first one down?

What the platform absorbs for you

AutoSSL issues and renews a certificate for the addon as soon as the name resolves here, so there is no second certificate to buy or install. The daily backup covers the new document root and its database without configuration, Softaculous will install any of 240+ applications into it in one click, and PHP version and extensions are set per site rather than per account — so a legacy application and a current one can share the plan.

What the platform cannot absorb is the shared fate. Both sites answer to the same account: the same suspension, the same resource ceiling, the same security posture. That is fine for your own projects. For a client's revenue-earning site, reseller hosting exists precisely so each account is walled off from the next.

An aisle of racks inside the London datacentre

The stack these instructions were measured on

Every command here was run against the platform we operate: cPanel, LiteSpeed Enterprise in front of NVMe storage, AutoSSL, and SSH on every shared tier. Nothing is written against a hypothetical host.

NVMe SSD storage behind a LiteSpeed cache is standard on every tier, from Sprint upwards — the cache layer is not a plan you upgrade into.

  • Commands you can paste, not screenshots to squint at
  • Per-tier limits quoted, so the maths is checkable
  • AutoSSL and daily backups handled by the platform
  • Engineers on the desk at any hour, including 3am

Why HostingFast

Standard on every plan

Numbers, not reassurance

Cores, RAM, database counts and disk allowances per tier, so you can work out whether the second site fits before you create it.

One command per claim

The curl one-liner for TTFB and the log query for per-host request counts are printed in full — nothing here is left as an exercise.

The nesting trap, explained

Not just do not nest the document root, but what nesting does to your URLs and to the .htaccess chain above the child site.

Written for someone with SSH

Full shell access with Git and Composer ships on every shared plan, so the guide assumes a terminal rather than avoiding one.

Honest about shared fate

An addon shares your resource ceiling and your suspension. Where that is the wrong answer, the guide says so and names the alternative.

Support that reads logs

Stuck on which vhost is eating the CPU allowance? The desk is staffed around the clock and will go through the access log with you.

Quick Start

From order to online

  1. 1

    Check the headroom before you create anything

    Open Resource Usage in cPanel and look at the CPU and entry-process peaks over the last week. An account already brushing its ceiling does not need a second site; it needs a bigger tier or a working cache.

  2. 2

    Point the nameservers, then create the vhost

    You can create the addon before DNS moves — the panel does not mind — but nothing serves and AutoSSL cannot validate until the name resolves here. Move delegation first and the rest lands in order.

  3. 3

    Set the document root outside public_html

    /domains/example.com, not public_html/example.com. Decline any offer to share a root with an existing site, and name the directory after the domain so the mapping is obvious a year from now.

  4. 4

    Verify the certificate and the cache header

    Once the name resolves, check both in one pass: curl -sI https://example.com | grep -iE 'HTTP/|x-litespeed-cache'. A 200 plus a hit on the second request means the vhost is fully wired, not just created.

  5. 5

    Baseline both hostnames, then compare later

    Record TTFB for the original site and the new one on the day you launch. Re-run the same command a fortnight on. If the first site has drifted, you now have evidence instead of a suspicion.

Built In

Loaded onto every plan

  • NVMe SSD storage behind a LiteSpeed cache on every tier, Sprint included
  • AutoSSL certificates issued and renewed for each vhost automatically
  • Full SSH access with Git and Composer on every shared plan
  • Per-site PHP version switching, so two apps can differ on one account
  • Softaculous installs 240+ applications into any document root in one click
  • A daily backup of files and databases, restorable from the panel yourself
  • In-place tier upgrades — Sprint to Turbo to Nitro without a migration
  • Renewal billed at the rate you signed up at, with no setup fee at any point
  • Money-back cover: 30 days on hosting plans, 7 on reseller
  • Human support on duty every hour of every day

Frequently Asked

What people ask us most often

Will a second site on the same account slow the first one down?

Only if the pair actually competes for the allowance. Two cached sites are close to free, because a LiteSpeed hit is served without touching PHP or MySQL. Two uncached applications on Sprint's or Turbo's single core will contend, and you will see it as a rising TTFB rather than as an error. Baseline both hostnames with curl before and a fortnight after, and the answer stops being a guess.

How do I work out which addon domain is burning the CPU?

Resource Usage in cPanel reports the account as a whole, so start there to confirm there is a problem, then attribute it from the logs: count requests per host in the raw access log and compare cache hit ratios between the two. On Nitro, PHP X-Ray on CloudLinux Pro goes one level deeper and names the slow request and function rather than the site.

How many sites does each tier actually allow?

Sprint runs one website, Turbo twenty-five and Nitro a hundred, with 25, 50 and 100 MySQL databases respectively and 10, 20 and 200 GB of NVMe storage. Those are ceilings, not recommendations — the practical limit is the combined load of everything you host, which is why the resource figures matter more than the site count.

Does the addon get its own certificate and cache, or share mine?

Its own, on both counts. AutoSSL issues a separate certificate per hostname as soon as it resolves here, and the LiteSpeed cache keys on the host, so purging one site does not empty the other. Mail is separate too. Resources, security posture and account suspension are what the pair genuinely shares.

Keep reading

Changing hosts? Run through our checklist first.

A straightforward sequence for a switch your visitors never feel: which files move first, how to shift email across without losing a single message, the right moment to repoint DNS, and the two mistakes behind almost all the downtime we get asked to rescue.

You'll get the checklist email, then occasional pointers on keeping a site running fast. Unsubscribe the moment you want out — the privacy policy covers the rest.

Two sites, one budget — make it a generous one.

NVMe behind a LiteSpeed cache on every tier, SSH with Git and Composer, AutoSSL that renews itself, and a renewal price identical to the one you signed up at.

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