subdomain

A  subdomain  typically refers to a domain with one more "name(dot)" component than that which someone actually has registered which is often seen indieweb sites with a family name domain like joel(dot)franusic(dot)com, or often on silos like matt(dot)wordpress(dot)com.

Most writing about IndieWeb assumes people will have their own second-level domain, like tantek.com, used just for themselves.

Joel Franusic
Joel Franusic uses joel.franusic.com as a way to separate given and family names, thus allowing for other subdomains for other Franusic family members.

Ben Roberts
Ben Roberts uses ben.thatmustbe.me - likely as a "domain hack" that reads as an English sentence.

David Shanske
David Shanske uses david.shanske.com as a way to separate given and family names.

Martijn van der Ven
used martijn.vanderven.se for a while but went back to using a path. Other family members are still on subdomains.

Lewis Cowles
has many non-canonical websites linking to their domain using the canonical representation tag to denote their primary, and legacy domain. lewis.cowles.uk is their attempt to have a longer-term and perhaps more accurate representation of their current nation, family name and their own name, separated as a subdomain from their family domain.

Silo Examples
The following silos give users subdomains:
 * Blogger
 * Known
 * LiveJournal (switched from path to subdomain in 2006, read why: lj2006
 * Tumblr
 * WordPress

The following silos used to use subdomains but switched away:
 * Slack used to use a per-team/community subdomain but, in 2019, switched to hosting everything under a single multi-tenant  endpoint.
 * This was for multiple reasons, the largest/most publicized one being for some of their performance improvements (since now multiple "teams" can share resources and a JS interpreter/Electron context/etc. for a single user on multiple teams). This also has some positive privacy side-effects:
 * Monitored networks can no longer trivially see which Slack communities someone is connected to (via packet inspection), since all identifying components of URIs are behind a TLS session
 * A network can't firewall off specific communities without removing access to all of Slack

Service Examples
Services that use or used subdomains and have switched to using paths instead or vice-versa.

Former service subdomain examples
In 2022, Google switched their Maps service from using a subdomain to using a path:
 * 2022-11-24 Smart Move, Google "… maps.google.com now redirects to google.com/maps. This implies that the permissions I give to Google Maps now apply to all of Googles services hosted under this domain"

Subdomain advantages disadvantages
Pros:


 * reduced cost and admin effort
 * each subdomain can be hosted at a different provider, allowing more flexibility for each person on the domain

Cons:


 * In a hypothetical example of alice.example.com, alice is dependent on example.com, although the dependency can potentially be very small, with example.com just managing a DNS "A" record for alice, pointing to alice's server.

Path alternative
Example: http://example.com/alice instead of http://alice.example.com/

If you use a URL with a path as your identity, your identity is vulnerable to the owner of the domain, and that any other site/path at that domain has CORS access to your identity.

If you are the owner of the domain, you should just use it directly without a path.

If you cannot or do not want to use just your domain, consider a subdomain instead of a path.

Path alternative advocates claim:
 * Advantage of path alternative: reduced cost and admin effort

However there is no escaping the downsides of path based identity:
 * Disadvantage: alice is locked into example.com; there's no way alice can leave.
 * Disadvantage: example.com can't allow alice to host arbitrary content without endangering their other users, because of the browser same-origin policy.

Indieweb Path Examples

 * Known multi-user sites provide paths instead of subdomains, because the configuration challenge for users to set up wildcard subdomains on shared hosts is too great. This is one challenge associated with shared hosting.
 * has his identity at https://vanderven.se/martijn/.

Silo Path Examples
The following silos give paths to users instead of subdomains:
 * Facebook
 * Instagram
 * Twitter

Other Path Examples
The following other sites use paths instead of subdomains:
 * Google Maps uses (since 2016-11-??) www.google.com/maps instead of maps.google.com which it used from launch 2015-02-08 until 2016-10-??, and which now redirects to www.google.com/maps.

Former Silo Path Examples
The following silos used to use paths for identity, and explicitly switched to using subdomains:
 * LiveJournal - see lj2006 for Livejournal's having to deal with this in 2006.

Conclusion
It seems okay to use subdomains for personal profiles as long as the 2nd-level domain holder makes a sufficient guarantee of subdomain portability. That is, they must let users change their DNS "A" records in perpetuity for no more than a minimal charge.

This seems reasonable with families, and perhaps also with fraternities, colleges, and other organizations to which one naturally has a life-long membership.

At some point, there may be companies willing to offer this kind of service with a plausible very-long-term commitment.

Note that taking advantage of free hosting that offers free subdomains leaves a lot of control of the domain in the hands of the host, putting your url at risk of a whole lot of things. Similarly, universities, etc, tend to not provide long-term stability.

Avoid www subdomain
Avoid using "www." on your domain.
 * It introduces an unnecessary security scoping (see above)