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A subdomain can be a useful tool in your website ecosystem, helping you scale projects, separate functional components, and create a more user-friendly structure. However, without careful setup and a clear purpose, it can complicate site management, create unnecessary technical burden, and reduce promotional efficiency. That’s why it’s crucial to understand how to use them correctly and what mistakes to avoid.
A subdomain, also known as a third-level domain, is the portion of a website’s address that comes before the main name and top-level domain:
Subdomains can be used to organize different sections of an existing website, such as a blog, online store, dashboard, API (Application Programming Interface), or mobile version of the website. They can also serve as standalone resources for launching personalized services and testing new ideas. For instance, for a blog, you might use ‘blog.example.com’, where ‘blog’ is a subdomain of ‘example.com’.
Companies that own a primary domain can use subdomains to separate different sections, services, or functional parts of a website into independent environments. This allows them to efficiently serve different target audience segments or create specialized sections for specific projects that seamlessly integrate with the main website. Other uses for subdomains include launching multilingual websites, marketing campaigns, and other tasks.
It’s important to understand that third-level domains can serve not just as a technical component of a website, but also as a fully-fledged website address. For instance, domains with the .it.com (second-level) extension operate on this principle: an address like ‘example.it.com’ is technically a third-level domain, but it’s used as a standalone domain for a website.
Owners of such addresses can also create subdomains such as ‘blog.example.it.com’. While such addresses may appear longer or more specific, for many companies this is a conscious choice. They help emphasize the business’s technology focus, launch a separate digital product, or establish a recognizable brand address.
Second-level domain extensions can also be used as regular subdomains for more focused or specialized projects. For example, if a company’s main website operates on ‘brand.com’, a separate IT blog, knowledge base, technical documentation, or new digital service can be hosted on ‘brand.it.com’. This helps logically separate the project, maintain brand affinity, and simultaneously highlight its technological specialization.
Subdomains are set up in your account on the registrar’s (a company where you can officially register and manage a domain name) or hosting provider’s website where the domain was registered. Almost all control panels work the same way, so the typical setup process is as follows:
The next step is to configure DNS (domain name system) records so they point to the correct server. DNS records are settings that link a domain to IP (Internet Protocol) addresses, email, and other services, helping to route internet traffic correctly.
In most cases, DNS records for a new subdomain are automatically configured by the service where the main domain name is located. However, if you need to do this manually, you will need to log in to the domain control panel, find the DNS section, and add a new record.
This will be an A or CNAME record that links the subdomain to the desired server or IP address.
Subdomains can be a great tool, but if they aren’t set up correctly, they can cause more problems than they’re worth; they can hinder SEO (Search Engine Optimization), confuse users, cause technical issues, and even negatively impact performance.
Let’s look at the five most common mistakes when using subdomains.
Source: Unsplash
One of the most common mistakes is creating a subdomain without a specific purpose, a thoughtful plan and the resources for its future support.
For instance, a company creates ‘blog.example.it.com’, but lacks the resources, content plan, or team to maintain it regularly, leading to the blog becoming abandoned and no longer updated. Or a company launches a separate subdomain for a sale, such as ‘sale.example.it.com’, even though it doesn’t have ongoing promotions or dedicated content. As a result, such a subdomain quickly becomes irrelevant and a redundant element of the website structure.
In such cases, a subdomain adds complexity without providing any real benefit. For smaller sections closely related to the main site, it’s often more effective to use subdirectories (a subcategory of the site, designated by a slash in the URL (Uniform Resource Locator), such as ‘example.it.com/blog’ or ‘example.it.com/sale’. They are easier to maintain because content, analytics, SEO, and navigation remain part of the site’s overall structure, and the user doesn’t have to perceive the additional section as a separate entity.
Why this is a problem
Without a clear purpose, a subdomain becomes an isolated element of the ecosystem. Furthermore, search engines often treat subdomains as separate entities. This means that the authority of the main domain isn’t always automatically transferred to the new address and needs to be built over time. A subdomain should solve a specific business problem. If it doesn’t, it’s more effective to use a section of the main website.
How to avoid
Before creating a subdomain, answer a few questions:
If there’s no clear answer, a subdomain may not be necessary and you can use subdirectories.
It’s worth choosing a subdirectory:
It’s worth choosing a subdomain:
The choice between a subdomain and a subdirectory depends on the site’s size and the degree of independence of its functional components. If you want to consolidate content, it’s better to use a subdirectory.
Source: Unsplash
One of the most dangerous mistakes when setting up subdomains is hosting identical or nearly identical content on both the primary domain and the subdomain. This happens when companies decide to move some information from subdirectories to a subdomain, for example, a blog on ‘blog.example.com’ while still leaving articles available at the old address ‘example.it.com/blog.’
This creates an ambiguous signal for search engines.
Why this is a problem
When duplicates exist, such as identical content on multiple subdomains, duplicate categories with pagination (?page=2, ?page=3), or regional versions of a site without proper configuration, the system automatically determines the canonical URL if the site owner hasn’t explicitly specified one using ‘canonical’ (a special HTML element that indicates to search engines which version of the page is considered the primary one) or ‘hreflang’ (an HTML attribute that specifies the language version and geographic targeting of a page) tags. This directly affects which version of the page will be displayed in search results.
For instance, if there are US and UK versions of a site on subdomains ‘us.example.it.com’ and ‘uk.example.it.com’ with identical English content but without properly configured ‘hreflang’ and ‘canonical’ tags, Google may start showing US pages to UK users and vice versa. As a result, users are directed to the wrong regional version of the site, and the business loses relevant traffic.
Therefore, duplicate content complicates SEO. If identical content is hosted on multiple URLs and ‘canonical’ tag, ‘hreflang’ tag, redirects, and indexing are configured incorrectly or are missing, search engines automatically select the preferred version, which isn’t always the one you want to promote.
This results in several problems:
This is especially critical for online stores and large projects, as they have a large number of similar pages, such as product pages, filters, categories, and regional versions. If such pages are duplicated on subdomains, the volume of duplicate content increases dramatically, and the scale of the problem becomes technically difficult to control.
How to avoid
To avoid this error, it’s essential to consider your site structure and technical settings in advance:
1. If duplication is unavoidable, use the ‘canonical’ tag. For instance, if the same product is available at two URLs, the duplicate page’s code specifies a link to the original:
2. If you use regional or language-specific subdomains, it’s essential to configure ‘hreflang’ tags. These tags help search engines understand which version of a page should be shown to users in different countries or languages:
3. For outdated or redundant copies, 301 redirects (permanent redirects from one URL to another) are used. For instance, if the page ‘example.it.com/shop’ is no longer needed, the user is automatically redirected to ‘shop.example.it.com.’ This helps transfer SEO value to the new page and eliminates competition between URLs.
4. Don’t forget about staging subdomains (test versions of a website that developers use to test updates before publishing). They are typically located at URLs like ‘staging.example.it.com’ or ‘dev.example.it.com.’ If such a subdomain is open for indexing, search engines may perceive it as a full-fledged website. Therefore, test versions should be blocked from indexing using the ‘noindex’ directive (a command for search engines not to include the page in search results). It looks like this:
It’s worth remembering that each subdomain should have its own value and not duplicate existing content.
Source: Unsplash
Without a proper approach to SEO, a subdomain can remain virtually invisible to search engines. And since it’s essentially a separate resource, independent of the main site, it also needs to be optimized separately.
Why this is a problem
Even high-quality content will yield no results if search engines can’t properly crawl and index the pages.
Typical errors include:
How to avoid
SEO for a subdomain should be built as a standalone project, not as a technical extension to the main website:
1. Add the subdomain to webmaster tools, such as Google Search Console, as a separate property. This will allow you to track indexing, crawl errors, and search queries.
2. It’s important to set up a separate sitemap (sitemap.xml) and ensure it’s accessible to search engines. This is especially important for a subdomain, as its pages aren’t always automatically indexed along with the main website.
Typically, a sitemap is created automatically via a CMS, SEO plugin, or site generator. The file is then placed at a location like ‘blog.example.it.com/sitemap.xml’ and submitted to Google Search Console. The sitemap should only include relevant pages that you want to be indexed.
3. It’s also crucial to consider the URL structure. They should be logical, readable, and consistent, such as ‘blog.example.it.com/seo-guide’ or ‘shop.example.it.com/category/shoes,’ rather than overly cluttered and uninformative URLs like ‘blog.example.com/archive/content/articles/2026/05/category/seo/post-78452-final-v2.’
4. Some attention should be paid to metadata such as a unique title and description for each page. These metadata shape search engines’ understanding of the page’s content and influence click-through rates in search results. It’s recommended that the title be 50-60 characters long, including the main keyword near the top. The description should be up to 150-160 characters long, with a brief and clear description of the page-s benefits. It might looks like these:
Meta tags should be unique for each page and reflect its actual content.
5. It’s also important to establish connections between the subdomain and the main website through links, menus, navigation, and contextual transitions:
This interlinking helps users quickly find the sections they need, and helps search engines better understand the project structure.
Source: Unsplash
A DNS record tells the internet where a website is located, where emails should be delivered, and how external services should interact with the domain.
If a subdomain becomes unavailable immediately after setup, the cause is most likely incorrectly configured DNS records. Even if the server is working correctly and the site is fully operational, an error at the DNS level can render the resource invisible to users.
Why this is a problem
Depending on the error in the DNS records, the browser will display a message about the resource being unavailable, an invalid address, or an infinite loading issue. Possible errors include:
Updates are a separate challenge. Even after the error is corrected, changes don’t propagate immediately. DNS servers around the world update data gradually, which can take anywhere from a few minutes to 48 hours.
If the TTL (Time To Live) - the parameter that determines how long a DNS record is cached - is set too high, updates will reach users even more slowly. For instance, a TTL of 86400 seconds means the record can be cached for up to 24 hours. If you change your IP address during this period, some users will continue to access the old server.
How to avoid
It’s essential to verify that all DNS settings are correct before publishing.
1. Select the correct record type:
It’s better to remember that you can’t use both an A record and a CNAME record at the same location for the same subdomain. This will cause a conflict.
2. Ensure that the IP address is current and matches the server hosting the website.
3. It’s best to set the TTL wisely:
This will allow you to make changes faster and reduce update delays.
4. After configuration, it’s recommended to check your records using DNS-checking services such as DNSChecker or WhatsMyDNS. These services show how the DNS record is propagating globally and whether it’s being resolved correctly in different regions.
DNS changes usually propagate quickly, but caching by providers and local networks can significantly increase the actual update time. Any error, even a small one, in the DNS can render the subdomain unavailable for hours or even days, so this step requires special attention.
Source: Unsplash
After making changes to a subdomain, developers often encounter a situation where users continue to see the old version of the website. The updated design, fixed errors, or new content have already been deployed to the server, but on the screen, everything appears unchanged.
Most often, this isn’t due to a publishing error, but to caching.
Caching is a temporary data storage mechanism to speed up website loading. It helps reduce server load and improves website performance. However, if the cache isn’t updated in a timely manner, users are shown an outdated version of the pages.
This can be caused by several storage levels:
Why this is a problem
The main problem is that it creates the false impression that updates haven’t been applied.
The developer may believe the site is malfunctioning, when in fact the server is already serving a new version, and the problem is only with the cached copy. The user, in turn, receives an outdated interface or old information.
This is especially critical after a redesign, urgent fixes, price updates, promotions, or technical errors. If part of the audience sees the old version of the site, this leads to confusion and a decrease in trust.
An uncontrolled cache can also interfere with testing; one team sees the updates, while another doesn’t.
How to avoid
After each release, you need to consider how exactly cached data is updated. Here’s what you can do:
1. Clear the cache manually where possible:
2. Configure Cache-Control headers (these are HTTP headers that determine how long a browser or CDN can store a copy of a file):
This header allows a file to be cached for one hour.
For critical resources that are frequently updated, you can use:
This forces the browser to check the relevance of the data before loading.
3. If you use a CDN, you should configure cache invalidation (forcefully removing outdated copies from distributed servers). For instance, after a website update, you can purge only specific files (style.css, main.js) or reset the entire project cache.
4. For static resources such as stylesheets (CSS), scripts (JavaScript), and images, it’s useful to use file versioning. This is a way to update files so the browser treats them as new and doesn't use the old cached copy.
For example, if you change the style.css file after a redesign, some users may continue to see the old version of the site because the browser has already cached this file. To force the update to download, append the version number to the file name:
Although the file remains the same, for the browser it’s a new URL, and it downloads the latest copy.
A more reliable option is to change the file name itself:
This allows the browser to download the new version of the file even if the old one is already cached.
5. Consider DNS propagation time. If you change the server or subdomain IP address, some users may continue to access the old route for some time due to the DNS cache.
Properly setting Cache-Control and a caching strategy directly impacts the balance between performance and content freshness.
Caching itself is useful and essential for website performance. However, without a systematic approach, it becomes a source of confusion that can make even a successful release look like a technical glitch.
—
A subdomain can be a valuable resource if used judiciously. However, mistakes during the planning and setup stages can result in lost traffic, technical failures, and unnecessary costs. Therefore, it’s crucial to handle its setup with the utmost care, recognizing it as the distinct asset it truly is. You should have a clear purpose, a well-thought-out architecture, a technical foundation, and a promotion strategy. Then it can become an efficient part of your digital ecosystem.
If the content is closely related to the main website, and the website itself doesn’t have many pages or information, it’s better to use a subdirectory (site.com/blog). If it’s a separate service, store, personal account, or regional version, a subdomain (blog.site.com, shop.site.com) would be more appropriate.
Indirectly, yes. Search engines may perceive a subdomain as a separate resource. This means it doesn’t always inherit the SEO authority of the main domain and requires its own optimization.
Yes. A subdomain should be added as a separate resource to track indexing, crawl errors, rankings, and search queries specifically for it.
Yes, if both contain the same or similar content. In this case, pages begin to compete with each other, and the search engine itself chooses which one to show.
Typically, it takes several days to several weeks. The speed depends on the site structure, the presence of a sitemap, internal linking, TTL, and overall domain authority.
Want to learn more about domain names? Visit it.com Domains blog and contact us on social media.
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What Is a Subdomain and When Does a Business Need One?
A subdomain, also known as a third-level domain, is the portion of a website’s address that comes before the main name and top-level domain:
Subdomains can be used to organize different sections of an existing website, such as a blog, online store, dashboard, API (Application Programming Interface), or mobile version of the website. They can also serve as standalone resources for launching personalized services and testing new ideas. For instance, for a blog, you might use ‘blog.example.com’, where ‘blog’ is a subdomain of ‘example.com’.
Companies that own a primary domain can use subdomains to separate different sections, services, or functional parts of a website into independent environments. This allows them to efficiently serve different target audience segments or create specialized sections for specific projects that seamlessly integrate with the main website. Other uses for subdomains include launching multilingual websites, marketing campaigns, and other tasks.
It’s important to understand that third-level domains can serve not just as a technical component of a website, but also as a fully-fledged website address. For instance, domains with the .it.com (second-level) extension operate on this principle: an address like ‘example.it.com’ is technically a third-level domain, but it’s used as a standalone domain for a website.
Owners of such addresses can also create subdomains such as ‘blog.example.it.com’. While such addresses may appear longer or more specific, for many companies this is a conscious choice. They help emphasize the business’s technology focus, launch a separate digital product, or establish a recognizable brand address.
Second-level domain extensions can also be used as regular subdomains for more focused or specialized projects. For example, if a company’s main website operates on ‘brand.com’, a separate IT blog, knowledge base, technical documentation, or new digital service can be hosted on ‘brand.it.com’. This helps logically separate the project, maintain brand affinity, and simultaneously highlight its technological specialization.
How to Set Up a Subdomain
Subdomains are set up in your account on the registrar’s (a company where you can officially register and manage a domain name) or hosting provider’s website where the domain was registered. Almost all control panels work the same way, so the typical setup process is as follows:
- Log in to your control panel.
- Click on the ‘Subdomains’ section.
- Enter a name. If you want to create a subdomain for a blog, use the word ‘blog’.
- Select the folder where the files will be stored. This can be a folder in the root of your hosting account or a newly created one.
- Confirm the subdomain creation, and it will be added.
The next step is to configure DNS (domain name system) records so they point to the correct server. DNS records are settings that link a domain to IP (Internet Protocol) addresses, email, and other services, helping to route internet traffic correctly.
In most cases, DNS records for a new subdomain are automatically configured by the service where the main domain name is located. However, if you need to do this manually, you will need to log in to the domain control panel, find the DNS section, and add a new record.
This will be an A or CNAME record that links the subdomain to the desired server or IP address.
Common Mistakes When Creating Subdomains
Subdomains can be a great tool, but if they aren’t set up correctly, they can cause more problems than they’re worth; they can hinder SEO (Search Engine Optimization), confuse users, cause technical issues, and even negatively impact performance.
Let’s look at the five most common mistakes when using subdomains.
1. Creating a Subdomain Without a Clear Purpose
Source: Unsplash
One of the most common mistakes is creating a subdomain without a specific purpose, a thoughtful plan and the resources for its future support.
For instance, a company creates ‘blog.example.it.com’, but lacks the resources, content plan, or team to maintain it regularly, leading to the blog becoming abandoned and no longer updated. Or a company launches a separate subdomain for a sale, such as ‘sale.example.it.com’, even though it doesn’t have ongoing promotions or dedicated content. As a result, such a subdomain quickly becomes irrelevant and a redundant element of the website structure.
In such cases, a subdomain adds complexity without providing any real benefit. For smaller sections closely related to the main site, it’s often more effective to use subdirectories (a subcategory of the site, designated by a slash in the URL (Uniform Resource Locator), such as ‘example.it.com/blog’ or ‘example.it.com/sale’. They are easier to maintain because content, analytics, SEO, and navigation remain part of the site’s overall structure, and the user doesn’t have to perceive the additional section as a separate entity.
Why this is a problem
Without a clear purpose, a subdomain becomes an isolated element of the ecosystem. Furthermore, search engines often treat subdomains as separate entities. This means that the authority of the main domain isn’t always automatically transferred to the new address and needs to be built over time. A subdomain should solve a specific business problem. If it doesn’t, it’s more effective to use a section of the main website.
How to avoid
Before creating a subdomain, answer a few questions:
- What problem does subdomain solve?
- Why can’t content be implemented in a subdirectory?
- Will the subdomain have a separate audience or functionality?
- Who will be responsible for its support?
If there’s no clear answer, a subdomain may not be necessary and you can use subdirectories.
It’s worth choosing a subdirectory:
- If the content is related to the main website and doesn’t require a separate infrastructure.
- For a blog, news section, or product catalog, if the site doesn’t have a multi-page structure and isn’t overloaded with information.
It’s worth choosing a subdomain:
- If a section of the site requires separate configuration, such as an online store, forum, or service.
- For regional versions of the site.
- You want or are needed to use different CMS (Content Management Systems).
The choice between a subdomain and a subdirectory depends on the site’s size and the degree of independence of its functional components. If you want to consolidate content, it’s better to use a subdirectory.
2. Duplicating Content
Source: Unsplash
One of the most dangerous mistakes when setting up subdomains is hosting identical or nearly identical content on both the primary domain and the subdomain. This happens when companies decide to move some information from subdirectories to a subdomain, for example, a blog on ‘blog.example.com’ while still leaving articles available at the old address ‘example.it.com/blog.’
This creates an ambiguous signal for search engines.
Why this is a problem
When duplicates exist, such as identical content on multiple subdomains, duplicate categories with pagination (?page=2, ?page=3), or regional versions of a site without proper configuration, the system automatically determines the canonical URL if the site owner hasn’t explicitly specified one using ‘canonical’ (a special HTML element that indicates to search engines which version of the page is considered the primary one) or ‘hreflang’ (an HTML attribute that specifies the language version and geographic targeting of a page) tags. This directly affects which version of the page will be displayed in search results.
For instance, if there are US and UK versions of a site on subdomains ‘us.example.it.com’ and ‘uk.example.it.com’ with identical English content but without properly configured ‘hreflang’ and ‘canonical’ tags, Google may start showing US pages to UK users and vice versa. As a result, users are directed to the wrong regional version of the site, and the business loses relevant traffic.
Therefore, duplicate content complicates SEO. If identical content is hosted on multiple URLs and ‘canonical’ tag, ‘hreflang’ tag, redirects, and indexing are configured incorrectly or are missing, search engines automatically select the preferred version, which isn’t always the one you want to promote.
This results in several problems:
- some pages may not be indexed;
- SEO value is distributed across multiple URLs instead of boosting a single key page;
- search engine rankings decline due to internal competition;
- search engine crawlers spend more resources crawling duplicates rather than truly important pages.
This is especially critical for online stores and large projects, as they have a large number of similar pages, such as product pages, filters, categories, and regional versions. If such pages are duplicated on subdomains, the volume of duplicate content increases dramatically, and the scale of the problem becomes technically difficult to control.
How to avoid
To avoid this error, it’s essential to consider your site structure and technical settings in advance:
1. If duplication is unavoidable, use the ‘canonical’ tag. For instance, if the same product is available at two URLs, the duplicate page’s code specifies a link to the original:
<link rel="canonical" href="https://example.it.com/product-1">2. If you use regional or language-specific subdomains, it’s essential to configure ‘hreflang’ tags. These tags help search engines understand which version of a page should be shown to users in different countries or languages:
<link rel="alternate" hreflang="en-us" href="https://us.example.it.com/" /><link rel="alternate" hreflang="en-gb" href="https://uk.example.it.com/" />3. For outdated or redundant copies, 301 redirects (permanent redirects from one URL to another) are used. For instance, if the page ‘example.it.com/shop’ is no longer needed, the user is automatically redirected to ‘shop.example.it.com.’ This helps transfer SEO value to the new page and eliminates competition between URLs.
4. Don’t forget about staging subdomains (test versions of a website that developers use to test updates before publishing). They are typically located at URLs like ‘staging.example.it.com’ or ‘dev.example.it.com.’ If such a subdomain is open for indexing, search engines may perceive it as a full-fledged website. Therefore, test versions should be blocked from indexing using the ‘noindex’ directive (a command for search engines not to include the page in search results). It looks like this:
<meta name="robots" content="noindex, nofollow">It’s worth remembering that each subdomain should have its own value and not duplicate existing content.
3. Ignoring Subdomain SEO
Source: Unsplash
Without a proper approach to SEO, a subdomain can remain virtually invisible to search engines. And since it’s essentially a separate resource, independent of the main site, it also needs to be optimized separately.
Why this is a problem
Even high-quality content will yield no results if search engines can’t properly crawl and index the pages.
Typical errors include:
- A missing ‘sitemap.xml’ file, which contains a list of the site’s pages and helps search engines find new content faster. It’s worth noting that a sitemap is especially useful for large sites, new projects, and resources with loosely linked pages, as it helps search engines discover content more effectively.
- An incorrectly configured ‘robots.txt’ file, which regulates search engine access to sections of the site, is also important. If ‘robots.txt’ accidentally blocks access to an entire subdomain, the pages simply won’t be visible to crawling bots.
- Non-unique meta tags (title, description) are page headings and descriptions that influence how search engines perceive them. Without unique meta tags, pages can compete with each other and risk losing relevance in search results.
- Lack of internal linking, which is connections between pages that help crawlers better understand the site’s structure.
- Lack of analytics and indexing tracking. Without analytics, it’s impossible to understand how a subdomain performs in search: which pages are indexed, where traffic drops, and which queries drive users.
How to avoid
SEO for a subdomain should be built as a standalone project, not as a technical extension to the main website:
1. Add the subdomain to webmaster tools, such as Google Search Console, as a separate property. This will allow you to track indexing, crawl errors, and search queries.
2. It’s important to set up a separate sitemap (sitemap.xml) and ensure it’s accessible to search engines. This is especially important for a subdomain, as its pages aren’t always automatically indexed along with the main website.
Typically, a sitemap is created automatically via a CMS, SEO plugin, or site generator. The file is then placed at a location like ‘blog.example.it.com/sitemap.xml’ and submitted to Google Search Console. The sitemap should only include relevant pages that you want to be indexed.
3. It’s also crucial to consider the URL structure. They should be logical, readable, and consistent, such as ‘blog.example.it.com/seo-guide’ or ‘shop.example.it.com/category/shoes,’ rather than overly cluttered and uninformative URLs like ‘blog.example.com/archive/content/articles/2026/05/category/seo/post-78452-final-v2.’
4. Some attention should be paid to metadata such as a unique title and description for each page. These metadata shape search engines’ understanding of the page’s content and influence click-through rates in search results. It’s recommended that the title be 50-60 characters long, including the main keyword near the top. The description should be up to 150-160 characters long, with a brief and clear description of the page-s benefits. It might looks like these:
- Meta Title: Subdomain SEO: How to Avoid Mistakes
- Meta Description: Practical recommendations for SEO settings for subdomains for businesses and web projects.
Meta tags should be unique for each page and reflect its actual content.
5. It’s also important to establish connections between the subdomain and the main website through links, menus, navigation, and contextual transitions:
- add a link to the blog in the main menu of the main website;
- place a ‘Read Also’ block with transitions between the domain and the subdomain;
- add links to key store sections from blog articles;
- use a unified footer with navigation across all company services.
This interlinking helps users quickly find the sections they need, and helps search engines better understand the project structure.
4. DNS Errors
Source: Unsplash
A DNS record tells the internet where a website is located, where emails should be delivered, and how external services should interact with the domain.
If a subdomain becomes unavailable immediately after setup, the cause is most likely incorrectly configured DNS records. Even if the server is working correctly and the site is fully operational, an error at the DNS level can render the resource invisible to users.
Why this is a problem
Depending on the error in the DNS records, the browser will display a message about the resource being unavailable, an invalid address, or an infinite loading issue. Possible errors include:
- an incorrect IP address (in this case, the subdomain will point to the wrong server);
- a conflict between the A record and the CNAME record;
- a missing DNS record for the required subdomain;
- an error in the record name, for instance, ‘blogs’ instead of ‘blog.’
Updates are a separate challenge. Even after the error is corrected, changes don’t propagate immediately. DNS servers around the world update data gradually, which can take anywhere from a few minutes to 48 hours.
If the TTL (Time To Live) - the parameter that determines how long a DNS record is cached - is set too high, updates will reach users even more slowly. For instance, a TTL of 86400 seconds means the record can be cached for up to 24 hours. If you change your IP address during this period, some users will continue to access the old server.
How to avoid
It’s essential to verify that all DNS settings are correct before publishing.
1. Select the correct record type:
- A record links a subdomain to a specific IP address, such as 192.0.2.1);
- CNAME record indicates that the subdomain is an alias for another domain, such as blog.example.com → example.com;
- TXT record is used for verification, email settings, and service data.
It’s better to remember that you can’t use both an A record and a CNAME record at the same location for the same subdomain. This will cause a conflict.
2. Ensure that the IP address is current and matches the server hosting the website.
3. It’s best to set the TTL wisely:
- it’s 300-600 seconds for testing;
- it’s 3600 seconds or higher for a stable production configuration.
This will allow you to make changes faster and reduce update delays.
4. After configuration, it’s recommended to check your records using DNS-checking services such as DNSChecker or WhatsMyDNS. These services show how the DNS record is propagating globally and whether it’s being resolved correctly in different regions.
DNS changes usually propagate quickly, but caching by providers and local networks can significantly increase the actual update time. Any error, even a small one, in the DNS can render the subdomain unavailable for hours or even days, so this step requires special attention.
5. Caching Issues
Source: Unsplash
After making changes to a subdomain, developers often encounter a situation where users continue to see the old version of the website. The updated design, fixed errors, or new content have already been deployed to the server, but on the screen, everything appears unchanged.
Most often, this isn’t due to a publishing error, but to caching.
Caching is a temporary data storage mechanism to speed up website loading. It helps reduce server load and improves website performance. However, if the cache isn’t updated in a timely manner, users are shown an outdated version of the pages.
This can be caused by several storage levels:
- browser cache: when website files (CSS - Cascading Style Sheets, JavaScript, images) are stored locally;
- CDN (Content Delivery Network) cache: copies of the website hosted on servers around the world;
- server caching: ready-made versions of pages stored on the hosting server;
- DNS cache: temporary storage of information about domain records.
Why this is a problem
The main problem is that it creates the false impression that updates haven’t been applied.
The developer may believe the site is malfunctioning, when in fact the server is already serving a new version, and the problem is only with the cached copy. The user, in turn, receives an outdated interface or old information.
This is especially critical after a redesign, urgent fixes, price updates, promotions, or technical errors. If part of the audience sees the old version of the site, this leads to confusion and a decrease in trust.
An uncontrolled cache can also interfere with testing; one team sees the updates, while another doesn’t.
How to avoid
After each release, you need to consider how exactly cached data is updated. Here’s what you can do:
1. Clear the cache manually where possible:
- in the CMS;
- on the server;
- in the CDN;
- in the browser during testing.
2. Configure Cache-Control headers (these are HTTP headers that determine how long a browser or CDN can store a copy of a file):
Cache-Control: max-age=3600This header allows a file to be cached for one hour.
For critical resources that are frequently updated, you can use:
Cache-Control: no-cacheThis forces the browser to check the relevance of the data before loading.
3. If you use a CDN, you should configure cache invalidation (forcefully removing outdated copies from distributed servers). For instance, after a website update, you can purge only specific files (style.css, main.js) or reset the entire project cache.
4. For static resources such as stylesheets (CSS), scripts (JavaScript), and images, it’s useful to use file versioning. This is a way to update files so the browser treats them as new and doesn't use the old cached copy.
For example, if you change the style.css file after a redesign, some users may continue to see the old version of the site because the browser has already cached this file. To force the update to download, append the version number to the file name:
- style.css?v=2
- app.js?v=2026
Although the file remains the same, for the browser it’s a new URL, and it downloads the latest copy.
A more reliable option is to change the file name itself:
- style.v2.css
- main.2026.js
This allows the browser to download the new version of the file even if the old one is already cached.
5. Consider DNS propagation time. If you change the server or subdomain IP address, some users may continue to access the old route for some time due to the DNS cache.
Properly setting Cache-Control and a caching strategy directly impacts the balance between performance and content freshness.
Caching itself is useful and essential for website performance. However, without a systematic approach, it becomes a source of confusion that can make even a successful release look like a technical glitch.
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A subdomain can be a valuable resource if used judiciously. However, mistakes during the planning and setup stages can result in lost traffic, technical failures, and unnecessary costs. Therefore, it’s crucial to handle its setup with the utmost care, recognizing it as the distinct asset it truly is. You should have a clear purpose, a well-thought-out architecture, a technical foundation, and a promotion strategy. Then it can become an efficient part of your digital ecosystem.
FAQs
When is it better to use a subdomain and when a subdirectory?
If the content is closely related to the main website, and the website itself doesn’t have many pages or information, it’s better to use a subdirectory (site.com/blog). If it’s a separate service, store, personal account, or regional version, a subdomain (blog.site.com, shop.site.com) would be more appropriate.
Does a subdomain affect the SEO of the main website?
Indirectly, yes. Search engines may perceive a subdomain as a separate resource. This means it doesn’t always inherit the SEO authority of the main domain and requires its own optimization.
Do I need to add a subdomain separately in Google Search Console?
Yes. A subdomain should be added as a separate resource to track indexing, crawl errors, rankings, and search queries specifically for it.
Can a subdomain compete with the main website in search results?
Yes, if both contain the same or similar content. In this case, pages begin to compete with each other, and the search engine itself chooses which one to show.
How quickly does a subdomain become indexed?
Typically, it takes several days to several weeks. The speed depends on the site structure, the presence of a sitemap, internal linking, TTL, and overall domain authority.
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